Document:

EX-4.2

 Exhibit 4.2 

Execution Copy 
 THIRD AMENDED AND
RESTATED STOCKHOLDERS’ AGREEMENT 
 THIS THIRD AMENDED AND RESTATED STOCKHOLDERS’ AGREEMENT, dated this 1st day of September, 2015
(this “Agreement”), is entered into by and among Proteostasis Therapeutics, Inc., a Delaware corporation (the “Corporation”); the holders of Series A Convertible Redeemable Preferred Stock, par value $.001 per
share of the Corporation (the “Series A Holders”) and the holders of Series B Convertible Redeemable Preferred Stock, par value $.001 per share of the Corporation (the “Series B Holders”) listed on
Schedule 1 attached hereto; and the persons listed as Principal Stockholders on Schedule 2 attached hereto (the “Principal Stockholders”). 

W I T N E S S E T H: 

WHEREAS, the Corporation, the Series A Holders (the “Existing Investors”) and certain Principal Stockholders are parties to
the Second Amended and Restated Stockholders’ Agreement dated May 20, 2011 (the “Prior Agreement”); 
 WHEREAS,
the Series B Holders are parties to that certain Series B Convertible Redeemable Preferred Stock Purchase Agreement, dated of even date herewith (the “Stock Purchase Agreement”), and hold shares of the Corporation’s
Series B Convertible Redeemable Preferred Stock, par value $.001 per share, and the Corporation desires to grant to all of the Series B Holders certain registration and other rights with respect to the Series B Preferred Stock; 

WHEREAS, the Series A Holders, the Series B Holders and the Principal Stockholders have agreed to certain restrictions on their rights to
vote or dispose of their shares of capital stock of the Corporation contained herein; and 
 WHEREAS, the Corporation, the Existing
Investors and the Principal Stockholders desire to amend and restate the Prior Agreement in the manner provided below. 
 NOW, THEREFORE,
the Existing Investors and the Principal Stockholders agree that the Prior Agreement shall be amended and restated in its entirety, and, in consideration of the foregoing and of the respective covenants and undertakings of the Corporation, the
Series A Holders, the Series B Holders and the Principal Stockholders hereunder, the parties hereto do further agree as follows. 
 1.
Definitions. As used herein, the following terms shall have the following respective meanings. 
 “Board” shall mean
the board of directors of the Corporation. 
 “Budget” shall have the meaning set forth in Section 2(h) hereof. 

“Certificate” shall mean the amended and restated certificate of incorporation of the Corporation, as amended and in effect
from time to time. 
 “Commission” shall mean the U.S. Securities and Exchange Commission. 

 “Common Stock” shall mean the Common Stock, par value $.001 per share, of the
Corporation. 
 “Common Stockholders” shall mean persons who are or become holders of Common Stock. 

“Elan” shall mean Elan Science One Ltd., a private company limited by shares organized under the laws of Ireland. 

“Environmental Laws” shall mean all applicable federal, state and local laws, ordinances, rules and regulations that
regulate, fix liability for, or otherwise relate to, the handling, use (including use in industrial processes, in construction, as building materials, or otherwise), storage and disposal of Hazardous Materials (as hereafter defined), and to the
discharge, leakage, presence, migration, threatened release or release (whether by disposal, a discharge into any water source or system or into the air, or otherwise) of any pollutant or effluent. Without limiting the preceding sentence, the term
“Environmental Laws” shall specifically include the following federal and state laws, as amended: 
 FEDERAL 

Comprehensive Environmental Response, Compensation and Liability Act of 1980, 42 U.S.C. 9601 et. seq.; 

Resource Conservation and Recovery Act of 1976, 42 U.S.C. 6901 et. seq.; 

Clean Water Act, 33 U.S.C. 1251 et. seq.; and 

Clean Air Act, 42 U.S.C. 7401 et. seq. 

STATE 
 MASSACHUSETTS
ENVIRONMENTAL STATUTES 
 Massachusetts Clean Waters Act, Mass. Gen. L. Ch. 21, Section 26, et. seq., and regulations
thereto; 
 Massachusetts Solid Waste Disposal Laws, Mass. Gen. L. Ch. 16, Section 18, et. seq., and Ch. 111, Section 105A,
and regulations thereto; 
 Massachusetts Oil and Hazardous Materials Release Prevention and Response Act, Mass. Gen. L., Ch. 21E,
Section 1, et. seq., and regulations thereto; 
 Massachusetts Solid Waste Facilities Law, Mass. Gen. L., Ch. 21H,
Section 1, et. seq., and regulations thereto; 

  
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 Massachusetts Toxic Use Reduction Act, Mass. Gen. L., Ch. 21I, Section 1, et. seq.,
and regulations thereto; 
 Massachusetts Litter Control Laws, Mass. Gen. L. Ch. 111, Section 150A, et. seq., and regulations
thereto; 
 Massachusetts Wetlands Protection Laws, Mass. Gen. L., Ch. 130, Section 105, et. seq., and regulations thereto; 

Massachusetts Environmental Air Pollution Control Law, Mass. Gen. L., Ch. 111, Section 2B, et. seq., and regulations thereto; 

Massachusetts Environmental Policy Act, Mass. Gen. L. Ch. 30, Section 61, et. seq., and regulations thereto; and 

Massachusetts Hazardous Waste Laws, Mass. Gen. L. Ch. 21C, Section 1, et. seq., and regulations thereto. 

“Equity Percentage” shall mean, as to any Preferred Stockholder, that percentage figure that expresses the ratio that
(a) the number of shares of issued and outstanding Common Stock then owned by such Preferred Stockholder bears to (b) the aggregate number of shares of issued and outstanding Common Stock then owned by all Stockholders. For purposes solely
of the computation set forth in clauses (a) and (b) above and Section 2(c) hereof, all (i) issued and outstanding securities, (ii) options to purchase same granted by the Corporation or (iii) outstanding warrants to
purchase same that, in the case of clause (i), (ii) or (iii) above, are convertible into, or exercisable or exchangeable for, (x) shares of Common Stock (including any issued and issuable shares of Preferred Stock) or
(y) any such convertible, exercisable or exchangeable securities shall be treated as having been so converted, exercised or exchanged at the rate or price at which such securities are convertible, exercisable or exchangeable for shares of
Common Stock in effect at the time in question (which, for purposes of Section 2(c) hereof, shall be at the time of delivery by the Corporation of the notice of the Offer contemplated by Section 2(c)(ii) hereof), whether or not such
securities are at such time immediately convertible, exercisable or exchangeable. 
 “Exchange Act” shall mean the
Securities Exchange Act of 1934, as amended. 
 “Exchange Act Registration Statement” shall have the meaning set forth in
Section 2(e) hereof. 
 “Excess Securities” shall have the meaning set forth in Section 2(c)(iv) hereof. 

“Excess Securities Notice” shall have the meaning set forth in Section 2(c)(iv) hereof. 

“Excess Securities Period” shall have the meaning set forth in Section 2(c)(iv)) hereof. 

“Excluded Forms” shall have the meaning given such term in Section 3(e) hereof. 

  
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 “Excluded Securities” shall mean, collectively: 

(A) Reserved Shares; 

(B) Common Stock issued or issuable to officers, directors or employees of, or consultants or independent contractors to, the
Corporation, pursuant to any written agreement, plan (including the Corporation’s 2008 Equity Incentive Plan) or arrangement to purchase, or rights to subscribe for, such Common Stock, including Common Stock issued under any amendment thereto
or any other equity incentive plan of the Corporation or other agreement that, in each case above (except the Corporation’s 2008 Equity Incentive Plan), (x) has been approved in form and in substance by the holders of at least two-thirds
of the combined voting power of the shares of Preferred Stock then outstanding, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by such
holders), and (y) as a condition precedent to the issuance of such shares, provides for the vesting of such shares and subjects such shares to restrictions on transfers, rights of first offer in favor of the Corporation and restricted-stock
grants to directors, employees or consultants as approved by the Board (including a majority of the Series A Directors); 

(C) Common Stock (or options, warrants or other securities convertible into or exercisable for Common Stock) issued as a stock
dividend payable in shares of Common Stock, or capital stock of any class issuable upon any subdivision, recombination, split-up or reverse stock split of all the outstanding shares of such class of capital stock; 

(D) Common Stock (or options, warrants or other securities convertible into or exercisable for Common Stock) issued or
issuable to banks or lenders in connection with a debt financing transaction or landlords in connection with real estate lease transactions, provided that each such issuance is approved by the Board (including a majority of the Series A
Directors); 
 (E) Common Stock (or options, warrants or other securities convertible into or exercisable for Common Stock)
issued or issuable to third parties in connection with strategic partnerships or alliances, joint ventures or other licensing transactions, provided that each such transaction and related issuance is approved by the Board (including a majority of
the Series A Directors); 
 (F) Common Stock (or options, warrants or other securities convertible into or exercisable
for Common Stock) issued or issuable pursuant to the acquisition by the Corporation of any other corporation, partnership, joint venture, trust or other entity by any merger, stock acquisition, reorganization, purchase of substantially all assets or
otherwise in which the Corporation, or its stockholders of record immediately prior to the effective date of such transaction, directly or indirectly, own at least two-thirds of the voting power of the acquired entity or the resulting entity after
such transaction, so long as approved by the Board (including a majority of the Series A Directors); 

  
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 (G) Common Stock (or options, warrants or other securities convertible into or
exercisable for Common Stock), the issuance of which is approved by two-thirds of the then-outstanding shares of Preferred Stock (including the “Requisite New Investors” (as that term is defined in the Certificate)), calculated in
accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by such holders), with such approval expressly waiving the application of the anti-dilution provisions
of Section A.7 of Article III of the Certificate as a result of such issuance (if applicable); 
 (H) 650,000
shares of Common Stock issued or issuable pursuant to, or in connection with, the License Agreement, dated as of August 11, 2008, by and among The Scripps Research Institute, The Salk Institute for Biological Studies and the Corporation; 

(I) Series A Preferred Stock issued pursuant to that certain Series A Convertible Redeemable Preferred Stock
Purchase Agreement, dated as of August 15, 2008, and that certain Second Series A Convertible Redeemable Preferred Stock Purchase Agreement, dated as of May 20, 2011, and the warrant to purchase 160,000 shares of Series A Preferred
Stock issued to the HCV Group, and the Common Stock issuable upon conversion of shares of Series A Preferred Stock. 

(J) Series B Preferred Stock issued or to be issued pursuant to the Stock Purchase Agreement and the Common Stock
issuable upon conversion of shares of Series B Preferred Stock. 
 “Fidelity Group” shall mean Beacon Bioventures
Fund II Limited Partnership as well as FMR LLC and FMR LLC’s affiliates; Fidelity International Ventures Limited, Fidelity Ventures IV-E Limited Partnership, Fidelity Ventures Principles IV-E Limited Partnership, Fidelity Investors VII Limited Partnership, Fidelity Capital Operating Limited Partnership, Fidelity Greater China Ventures Fund Limited Partnership, Beacon Bioventures
Limited Partnership, Beacon Bioventures Principals Limited Partnership, Beacon Bioventures Fund III Limited Partnership, Beacon Bioventures Fund IV Limited Partnership, Fidelity Foundation, Fidelity Non-Profit Management Foundation, the
Edward C. Johnson Fund, FIL Limited and FIL Limited’s affiliates; Fidelity Investors Limited Partnership, Fidelity Investors II Limited Partnership, Fidelity Investors III Limited Partnership, Fidelity Investors IV Limited
Partnership, Fidelity Investors Management Corp., Fidelity Investors V Limited Partnership, Fidelity Investors VI Limited Partnership, FILP Capital Reserves Limited Partnership, Fidelity Seaport Limited Partnership, Fidelity Real Estate
Limited Partnership and any other entity that is directly or indirectly owned or controlled by members of FMR LLC; Fidelity Ventures II Limited Partnership, Fidelity Ventures III Limited Partnership, Fidelity Venture IV Limited
Partnership, Fidelity Ventures Limited, Fidelity Ventures Principals I, LLC, Fidelity Ventures Principal II, LLC, and Fidelity Ventures Principal III, LLC, and Fidelity Ventures Principal IV; and Fidelity Biosciences
Advisors LLC and Fidelity Biosciences Corp., FMR LLC’s affiliates and FIL 

  
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Limited’s affiliates shall include any person directly or indirectly controlling, controlled by, or under direct or indirect common control with FMR LLC or FIL Limited, as the case may be,
including (a) any person who is an officer, director, employee, manager, member, managing members, general partners, limited partner, or direct or indirect beneficial holder of the then outstanding interests or capital stock of FMR LLC or
FIL Limited, as the case may be, or any of their respective affiliates, (b) any person of which FMR LLC or FIL Limited, as the case may be, directly or indirectly, either beneficially own(s) at least 5% of the then-outstanding equity securities
or constitute(s) at least a 5% equity participant and (c) all investment vehicles or other entities for which FMR LLC or FIL Limited, as the case may be, or any of its affiliates (as defined in clauses (a) and (b) above) serve as a
manager, member, general partner or investment adviser or in a similar capacity, and all investment vehicles or other entities under the direct or indirect ownership, control or management of FMR LLC or FIL Limited or any of their respective
affiliates (as defined in clauses (a) and (b) above). 
 “Group” shall mean (a) as to a Preferred
Stockholder that is a limited partnership or corporation, any and all limited partnerships, limited liability companies, or corporations now existing or hereafter formed that are affiliated with or under common control with such Preferred
Stockholder and any predecessor or successor thereto, (b) in the case of HCV VIII, the HCV Group, (c) as to Beacon Bioventures Fund II Limited Partnership, the Fidelity Group, (d) as to any limited partnership, to the
limited partners of such partnership upon the dissolution thereof, (e) as to any limited liability company, any of the members thereof, (f) as to any Series A Holder, any other Series A Holder, (g) as to any Series B
Holder, any other Series B Holder, and (h) as to any individual, such individual’s estate, heirs, executors and legal representatives. 

“Hazardous Materials” shall include, without limitation, any flammable explosives, petroleum products, petroleum byproducts,
radioactive materials, hazardous wastes, hazardous substances, toxic substances or other similar materials regulated by Environmental Laws. 

“HCV Group” shall mean (a) HCV VIII, (b) any venture-capital limited partnership now existing or hereafter
formed that is affiliated, or under common control, with one or more general partners of HCV VIII (an “HCV Fund”), (c) any limited partners or affiliates of HCV VIII or any other HCV Fund and (d) any successors
or assigns of any of the foregoing. 
 “HCV VIII” shall mean HealthCare Ventures VIII, L.P., a Delaware limited
partnership, including any successor thereto or any assignee of the interest, in whole or in part, of HCV VIII hereunder. 

“Notice of Acceptance” shall have the meaning set forth in Section 2(c)(iii) hereof. 

“Offer” shall have the meaning set forth in Section 2(c)(ii) hereof. 

“Offered Securities” shall mean, except for Excluded Securities, (a) any shares of Common Stock, Preferred Stock or any
other equity security of the Corporation, (b) any debt security or capitalized lease with any equity feature with respect to the Corporation or (c) any option, warrant or other right to subscribe for, purchase or otherwise acquire any such
equity security, debt security or capitalized lease. 

  
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 “Other Shares” shall have the meaning set forth in Section 3(e)(v) hereof.

 “Person” shall mean any individual, partnership, corporation, group, trust or other legal entity. 

“Preferred Stock” shall mean the Series A Preferred Stock and the Series B Preferred Stock. 

“Preferred Stockholder” shall mean a holder of the Series A Preferred Stock or the Series B Preferred Stock. 

“Principal Stockholders” shall mean those persons identified on Schedule 2 hereto. 

“Property” shall include, without limitation, land, buildings and laboratory facilities owned or leased by the Corporation or
as to which the Corporation now has any duties, responsibilities (for clean-up, remedy or otherwise) or liabilities under any Environmental Laws, or as to which the Corporation or any subsidiary of the Corporation may have such duties,
responsibilities or liabilities because of past acts or omissions of the Corporation or any such subsidiary or their predecessors, or because the Corporation or any such subsidiary or their predecessors in the past was such an owner or operator of,
or bore some other relationship with, such land, buildings or laboratory facilities. 
 “Qualified Public Offering” shall
mean a firm commitment underwritten public offering of Common Stock of the Corporation in the United States registered under the Securities Act, pursuant to which (a) the net proceeds to the Corporation are at least $50,000,000 and (b) the
Common Stock is listed on either the National Association of Securities Dealers Automated Quotation System (“NASDAQ”) or the New York Stock Exchange (“NYSE”). 

“Refused Securities” shall have the meaning set forth in Section 2(c)(vi) hereof. 

“Reserved Shares” shall mean the shares of Common Stock reserved by the Corporation for issuance upon conversion of the
Preferred Stock. 
 “Restricted Securities” shall mean any of the Preferred Stock and the Common Stock issued or issuable
upon the conversion of the Preferred Stock, all shares of Common Stock issued or issuable in respect thereof by way of stock splits, stock dividends, stock combinations, recapitalizations or like occurrences, and any other shares of Common Stock or
other securities of the Corporation that may be issued hereafter to any of the Preferred Stockholders or any member of their Group that are convertible into or exercisable for shares of Common Stock (including, without limitation, other classes or
series of convertible preferred stock, warrants, options or other rights to purchase Common Stock or convertible debentures or other convertible debt securities) and the Common Stock issued or issuable upon such conversion or exercise of such other
securities, that, in each case above, have not been sold (a) in connection with an effective registration statement filed pursuant to the Securities Act or (b) pursuant to Rule 144 or Rule 144A promulgated by the Commission under the
Securities Act. 

  
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 “Restricted Shares” shall mean the shares of Common Stock issued or issuable
upon the conversion or exchange of Restricted Securities or otherwise constituting a portion of Restricted Securities. 

“Securities Act” shall mean the Securities Act of 1933, as amended. 

“Series A Directors” shall mean the members of the Board designated by certain of the Investors under
Section 5(a)(ii) hereof. 
 “Series A Holders” shall mean the holders of Series A Convertible Redeemable
Preferred Stock, par value $.001 per share of the Corporation. 
 “Series A Preferred Stock” shall mean Series A
Convertible Redeemable Preferred Stock, par value $.001 per share, of the Corporation. 
 “Series B Holders” shall
have the meaning set forth in the preamble hereto. 
 “Series B Preferred Stock” shall mean Series B Convertible
Redeemable Preferred Stock, par value $.001 per share, of the Corporation. 
 “Stockholders” shall mean all holders of
capital stock of the Corporation. 
 “Target Month” shall have the meaning set forth in Section 2(g)(i) hereof. 

“Transfer” shall include any disposition of any Restricted Securities or of any interest therein that would constitute a sale
thereof within the meaning of the Securities Act. 
 “20-Day Period” shall have the meaning set forth in
Section 2(c)(ii) hereof. 
 2. Certain Covenants of the Corporation. 

(a) Meetings of the Board. The Corporation shall call, and use its best efforts to have, regular meetings of the Board not less often
than quarterly. The Corporation shall pay all reasonable and appropriately documented travel expenses and other out-of-pocket expenses incurred by directors and board observers, if any, who are not employed by the Corporation in connection with
attendance at meetings to transact the business of the Corporation or attendance at meetings of the Board or any committee thereof. 
 (b)
Reservation of Shares of Common Stock and Preferred Stock, etc. The Corporation shall at all times have authorized and reserved out of its authorized but unissued shares of Common Stock, a sufficient number of shares of Common Stock to
provide for the conversion of the Preferred Stock. Neither the issuance of the Preferred Stock nor the shares of Common Stock issuable upon the conversion of the Preferred Stock shall be subject to a preemptive right of any other Stockholder. 

(c) Right of First Refusal. 

(i) The Corporation shall not issue, sell or exchange, agree to issue, sell or exchange, or reserve or set aside for issuance,
sale or exchange, any Offered Securities 

  
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unless in each case the Corporation shall have first offered to sell to the Preferred Stockholders all of such Offered Securities on the terms set forth herein. Each Preferred Stockholder shall
be entitled to purchase up to its Equity Percentage of the Offered Securities. Each Preferred Stockholder may delegate its rights and obligations with respect to such Offer to one or more members of its Group, which members shall thereafter be
deemed to be a “Preferred Stockholder” as applicable, for the purpose of applying this Section 2(c) to such Offer. For the avoidance of doubt, each Preferred Stockholder is waiving its right to purchase its Equity Percentage of the
Series B Preferred Stock and accepts the allocations set forth in Schedule I of the Series B Preferred Stock Purchase Agreement of even date herewith. 

(ii) The Corporation shall deliver to each Preferred Stockholder written notice of the offer to sell the Offered Securities,
specifying the price and terms and conditions of the offer (the “Offer”). The Offer by its terms shall remain open and irrevocable for a period of 20 days from the date of its delivery to such Preferred Stockholder (the
“20-Day Period”), subject to extension to include the Excess Securities Period (as such term is hereinafter defined). 

(iii) Each Preferred Stockholder shall evidence its intention to accept the Offer by delivering a written notice signed by such
Preferred Stockholder setting forth the number of shares that such Preferred Stockholder elects to purchase (the “Notice of Acceptance”). The Notice of Acceptance must be delivered to the Corporation prior to the end of the 20-Day
Period. The failure by a Preferred Stockholder to exercise its rights hereunder shall not constitute a waiver of any other rights or of the right to receive notice of and participate in any subsequent Offer. 

(iv) If any Preferred Stockholder fails to exercise its right hereunder to purchase its Equity Percentage of the Offered
Securities, the Corporation shall so notify the other Preferred Stockholders in a written notice (the “Excess Securities Notice”). The Excess Securities Notice shall be given by the Corporation promptly after it learns of any
Preferred Stockholder’s intention not to purchase all of its Equity Percentage of the Offered Securities, but in no event later than ten (10) days after the expiration of the 20-Day Period. The Preferred Stockholders that have agreed to
purchase their Equity Percentage of the Offered Securities shall have the right to purchase the portion not purchased by such Preferred Stockholder (the “Excess Securities”), on a pro rata basis, by giving notice
within ten (10) days after receipt of the Excess Securities Notice from the Corporation. The twenty (20) day period during which (A) the Corporation must give the Excess Securities Notice to the other Preferred Stockholders and
(B) each of the other Preferred Stockholders must give the Corporation notice of its intention to purchase all or any portion of its pro rata share of the Excess Securities is hereinafter referred to as the “Excess
Securities Period.” 
 (v) If the Preferred Stockholders tender their Notice of Acceptance prior to the end of the
20-Day Period indicating their intention to purchase all of the Offered Securities or, if prior to the termination of the Excess Securities Period, the Preferred Stockholders tender Excess Securities Notices to purchase all of the Excess Securities,
the Corporation shall schedule a closing of the sale of all such Offered Securities. Upon the closing of the sale of the Offered Securities to be purchased by the Preferred Stockholders, 

  
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each Preferred Stockholder shall (A) purchase from the Corporation that portion of the Offered Securities (including the Excess Securities) for which it tendered a Notice of Acceptance and
an Excess Securities Notice, if applicable, upon the terms specified in the Offer and (B) execute and deliver an agreement further restricting transfer of such Offered Securities substantially as set forth in Sections 3(a), 3(b) and 3(c)
hereof. In addition, with respect to the Offered Securities being purchased by the Preferred Stockholders, the Corporation shall provide each such Preferred Stockholder with the rights and benefits set forth herein. The obligation of the Preferred
Stockholders to purchase such Offered Securities is further conditioned upon the preparation of a purchase agreement embodying the terms of the Offer, which agreement shall be reasonably satisfactory in form and substance to the Preferred
Stockholders and their respective counsel. 
 (vi) The Corporation shall have ninety (90) days from the expiration of
the 20-Day Period, or the Excess Securities Period, if applicable, to sell the Offered Securities (including the Excess Securities) refused by the Preferred Stockholders (the “Refused Securities”) to any other person or persons, but
only upon terms and conditions that are in all material respects (including, without limitation, price and interest rate) no more favorable to such other person or persons, and no less favorable to the Corporation than those terms and conditions set
forth in the Offer. Upon and subject to the closing of the sale of all of the Refused Securities (which shall include full payment to the Corporation), each Preferred Stockholder shall (A) purchase from the Corporation those Offered Securities
(including the Excess Securities) for which it tendered a Notice of Acceptance and an Excess Securities Notice, if applicable, upon the terms specified in the Offer and (B) execute and deliver an agreement restricting transfer of such Offered
Securities (including the Excess Securities) substantially as set forth in Sections 3(a), 3(b) and 3(c) hereof. In addition, with respect to the Offered Securities being purchased by the Preferred Stockholders, the Corporation shall provide
each such Preferred Stockholder with the rights and benefits set forth herein. The Corporation agrees, as a condition precedent to accepting payment for and making delivery of any Refused Securities to any executive officer, employee, consultant or
independent contractor of or to the Corporation, or to any other person, to have each and every such person execute and deliver a stock restriction agreement in the form approved by the Board (including a majority of the Series A Directors) to
the extent such purchaser has not already executed such Agreement. The obligation of the Preferred Stockholders to purchase such Offered Securities (including the Excess Securities) is further conditioned upon the preparation of a purchase agreement
embodying the terms of the Offer, which agreement shall be reasonably satisfactory in form and substance to such Preferred Stockholders and their respective counsel. 

(vii) In each case, any Offered Securities not purchased either by the Preferred Stockholders, or by any other person in
accordance with this Section 2(c) may not be sold or otherwise disposed of until they are again offered to the Preferred Stockholders under the procedures specified in Sections 2(c)(i), (ii), (iii), (iv), (v) and (vi) hereof.

 (viii) Each Preferred Stockholder may, by prior written consent, waive its rights under this Section 2(c);
provided, however, that such rights may be waived on behalf of all Preferred Stockholders by the vote of two-thirds of the Preferred Stockholders (including the vote of the Requisite New Investors (as defined in the Certificate)). Such
a waiver shall be deemed a limited waiver and shall only apply to the extent specifically set forth in the written consent of such Preferred Stockholder. 

  
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 (d) Negative Covenants. 

(i) Majority Approvals. The Corporation shall not, directly or indirectly, take any of the actions specified in
Section A.6(d) of Article III of the Certificate without the prior written consent or vote of the holders of a majority of the then-outstanding Preferred Stock determined in accordance with Section A.6(a) of Article III of the
Certificate. 
 (ii) Stock and Option Agreements. Without the prior written consent or vote of the holders of
two-thirds of the then-outstanding Preferred Stock, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by such holders), the Corporation
shall not issue any shares of Common Stock or options, warrants or other rights to acquire Common Stock or other securities of the Corporation to any employee, officer, director, consultant, independent contractor or other person or entity except
for Excluded Securities. 
 (iii) Registration Rights. The Corporation shall not hereafter grant to any persons any
rights to register or qualify stock of the Corporation under federal or state securities laws, which rights are equal or senior to the rights of the Preferred Stock, unless it shall have first obtained the written consent of the holders of at least
two-thirds of the combined voting power of the Preferred Stock then outstanding, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by such
holders). 
 (e) Filing of Reports Under the Exchange Act. 

(i) The Corporation shall give prompt notice to the holders of Preferred Stock of (A) the filing of any registration
statement (an “Exchange Act Registration Statement”) pursuant to the Exchange Act, relating to any class of equity securities of the Corporation, (B) the effectiveness of such Exchange Act Registration Statement and
(C) the number of shares of such class of equity securities outstanding, as reported in such Exchange Act Registration Statement, in order to enable the Preferred Stockholders to comply with any reporting requirements under the Exchange Act or
the Securities Act. Upon the written request of two-thirds in interest of the Preferred Stockholders, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted
Shares held by such holders), the Corporation shall use commercially reasonable efforts to, at any time after the Corporation has registered any shares of Common Stock under the Securities Act, file an Exchange Act Registration Statement relating to
any class of equity securities of the Corporation then held by the Preferred Stockholders or issuable upon conversion or exercise of any class of debt or equity securities or warrants or options of the Corporation then held by the Preferred
Stockholders, whether or not the class of equity securities with respect to which such request is made shall be held by the number of persons that would require the filing of a registration statement under Section 12(g)(1) of the Exchange Act.

  
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 (ii) If the Corporation shall have filed an Exchange Act Registration Statement
or a registration statement (including an offering circular under Regulation A promulgated under the Securities Act) pursuant to the requirements of the Securities Act, which statement shall have become effective (and in any event, at all times
following the initial public offering of any of the securities of the Corporation), then the Corporation shall use commercially reasonable efforts to comply with all of the reporting requirements of the Exchange Act (whether or not it shall be
required to do so) and shall comply with all other public information reporting requirements of the Commission as a condition to the availability of an exemption from the Securities Act for the sale of any of the Restricted Securities by any holder
of Restricted Securities (including any such exemption pursuant to Rule 144 or Rule 144A thereof, as amended from time to time, or any successor rule thereto or otherwise). The Corporation shall cooperate with each holder of Restricted Securities in
supplying such information as may be necessary for such holder of Restricted Securities to complete and file any information reporting forms presently or hereafter required by the Commission as a condition to the availability of an exemption from
the Securities Act (under Rule 144 or Rule 144A thereunder or otherwise) for the sale of any of the Restricted Securities by any holder of Restricted Securities. 

(f) Access to Records. The Corporation shall afford to each of the Preferred Stockholders and such Preferred Stockholder’s
employees, counsel and other authorized representatives, free and full access, at all reasonable times and for reasonable periods of time, to all of the books, records and properties of the Corporation and to all officers and employees of the
Corporation. 
 (g) Financial Reports. Until such time that the Corporation has a class of its equity securities registered under the
Exchange Act and is required to file reports thereunder pursuant to Sections 13 or 15(d) of the Exchange Act, except with respect to the obligation set forth in Section 2(g)(v)(A) hereof that shall survive such time, the Corporation shall
furnish each of the Preferred Stockholders with the financial information described below (unless any such requirements are waived by the Preferred Stockholders). 

(i) Within 30 days after the last day of each month (the “Target Month”) (or such other calendar period as is
approved by the Board), Target Month financial statements, including a balance sheet as of the last date of such Target Month, a statement of income (or monthly operating expenses) for such month, together with a cumulative statement of income from
the first day of the current year to the last day of such month, which statements shall be prepared from the books and records of the Corporation, a cash flow analysis, together with cumulative cash flow analyses from the first day of the current
year to the last day of such month, and a comparison between the actual monthly operating expenses and the projected figures for such month and the comparable figures for the prior year, subject to the provisions of Section 2(c)(i) hereof. 

(ii) Within 45 days after the end of each quarterly accounting period, unaudited financial statements for such quarterly
accounting period, certified by the Chief Financial Officer or the Treasurer of the Corporation, as presenting fairly the financial condition and results of operations of the Corporation and as having been prepared on a basis consistent with the
accounting principles reflected in the Corporation’s annual audited financial statements, accompanied by a report, signed by the Chief Financial Officer or the 

  
 12 

 
Treasurer of the Corporation, summarizing the operating and financial highlights of the Corporation for such quarterly accounting period, which report shall include (A) a comparison between
the actual quarterly operating and financial results, the Budget (as defined in Section 2(h) hereof) and the results of the similar quarterly accounting period for the prior fiscal year of the Corporation, together with an explanation of
material variances from the Budget and such similar quarterly accounting period, as the case may be, and (B) a narrative analysis of operations and trends in the business of the Corporation during such quarterly accounting period. 

(iii) Within 120 days after the end of each fiscal year of the Corporation, audited financial statements of the Corporation,
which statements shall include an income statement and a statement of cash flow for such fiscal year and a balance sheet as of the last day thereof, each prepared in accordance with generally accepted accounting principles consistently applied, and
accompanied by the report of such independent certified public accountants as shall have been approved by the Board. 
 (iv)
If for any period the Corporation shall have any subsidiary or subsidiaries whose accounts are consolidated with those of the Corporation, then the financial statements delivered for such period pursuant to Sections 2(g)(i), (ii) and
(iii) hereof shall be the consolidated and consolidating financial statements of the Corporation for all such consolidated subsidiaries. 

(v) Promptly upon becoming available: 

(A) copies of all financial statements, reports, press releases, notices, proxy statements and other documents sent by the
Corporation to its Stockholders or released to the public and copies of all regular and periodic reports, if any, filed by the Corporation with the Commission or any securities exchange or self-regulatory organization; and 

(B) any other financial or other information available to management of the Corporation that any of the Preferred Stockholders
shall have reasonably requested on a timely basis. 
 (h) Budget and Operating Forecast. The Corporation shall prepare and submit to
the Board and each of the Preferred Stockholders an operating plan with monthly and quarterly breakdowns (the “Budget”) for each fiscal year at least 30 days prior to the beginning of each fiscal year of the Corporation. The Budget
shall be deemed accepted as the Budget for such fiscal year only when it has been approved by the Board (including a majority of the Series A Directors). The Budget shall be reviewed by the Corporation periodically, and all changes therein, and
all material deviations therefrom, shall be reviewed by the Board on at least a quarterly basis. The obligation of the Corporation to furnish the Budget shall terminate upon the consummation of a Qualified Public Offering. 

(i) System of Accounting. The Corporation shall maintain, and cause each of its subsidiaries, when and if any shall exist, to maintain,
its books of accounts, related records and system of accounting in accordance with good business practices and generally accepted accounting principles, and shall cause the matters contained therein to be appropriately and accurately reflected in
the financial reports (which shall be prepared in accordance with generally accepted accounting principles) furnished pursuant hereto. 

  
 13 

 (j) Restriction on Transfer Rights; Confidentiality. The rights granted to each of the
Preferred Stockholders pursuant to Sections 2(f) through 2(h) hereof (the “Financial Information Rights”) shall not be transferred or assigned by any Preferred Stockholder to, and shall not inure to the benefit of, any
successor, transferee or assignee of any Preferred Stockholder or member of the Preferred Stockholder’s Group that, in each case, is engaged in any business directly competitive with the Corporation. 

(k) Confidentiality and Non-Competition Agreements for Key Employees. The Corporation shall cause each person who is presently an
employee of or a consultant or independent contractor to the Corporation or who becomes an employee of or a consultant to the Corporation subsequent to the date hereof and who shall have or be proposed to have access to confidential or proprietary
information of the Corporation to execute a confidentiality and non-competition agreement in form and substance attached hereto as Exhibit A or B or otherwise approved by the Board prior to the commencement of such person’s
employment by the Corporation in such capacity. 
 (l) Stock Restriction Agreement for Directors, Officers, Employees and Consultants Who
Are or Become Stockholders. The Corporation shall cause each of its directors, officers, employees, consultants or independent contractors who own any shares of capital stock of the Corporation representing greater than one percent (1%) of
the total outstanding capital stock of the Corporation, or any options, warrants or other rights to purchase any shares of such capital stock, or who may own in the future any such shares, or options, warrants or other rights to purchase such
shares, to execute a stock restriction agreement in the form approved by the Board (including a majority of the Series A Directors) prior, and as a condition, to the acquisition of such shares, or options, warrants or rights, by such person.

 (m) Marketing and Promotional Material. Each of the Preferred Stockholders will have the right to review and approve, in advance
of publication, distribution or dissemination, any reference to such Preferred Stockholder or any entity affiliated with such Preferred Stockholder (other than the Corporation), contained in any document, instrument, report or filing or in any
advertising, marketing, promotional and similar materials. 
 (n) Environmental Matters. The Corporation shall promptly advise the
Preferred Stockholders in writing of any pending or threatened claim, demand or action by any governmental authority or third party relating to any Hazardous Materials affecting the Property of which it has knowledge. The Corporation shall not
discharge, place, release, spill or dispose of any Hazardous Materials or any other pollutants or effluents upon the Property or elsewhere (including, but not limited to, underground injection of such substances), and the Corporation shall not
discharge into the air any emission that would require a permit under the Clean Air Act or its state counterparts or any other Environmental Laws, except (x) if the Corporation had obtained such a permit or (y) in compliance with the
Environmental Laws. The Stockholders of the Corporation shall have no control over, or authority with respect to, the waste disposal operations of the Corporation. The Corporation hereby indemnifies, defends and holds harmless the Preferred
Stockholders from and against any and all manner of actions, causes of action, suits, debts, accounts, controversies, judgments, claims, demands, losses or liabilities of any 

  
 14 

 
nature (including reasonable attorneys’ fees) directly or indirectly arising out of or attributable to (i) any misrepresentation or breach of the representations and covenants set forth
in Section 5.17 of the Stock Purchase Agreement or (ii) the use, generation, storage, release, threatened release, discharge, disposal or presence of Hazardous Materials on, under or about the Property by any person during the period that
the Corporation was the legal or equitable owner of the Property or that occurred prior to such time and was otherwise actually known by, or should have been known by, the Corporation. The obligation of the Corporation to indemnify the Preferred
Stockholders shall specifically cover and include, without limitation, all fines and penalties imposed by federal, state or local authorities, costs of removing or neutralizing the Hazardous Materials, injury to the property adjoining the Property,
injury to persons living or working on or about the Property or adjoining or otherwise affecting property, and all other indirect or consequential damages incurred by the Preferred Stockholders. 

(o) Material Changes and Litigation. The Corporation shall promptly notify the Preferred Stockholders of any material adverse change in
the business, operations, conditions or prospects of the Corporation taken as a whole and of any litigation or governmental proceeding or investigation brought or, to the best of the Corporation’s knowledge, threatened against the Corporation
or any Common Stockholder, officer, director, key employee or principal stockholder of the Corporation that, if adversely determined, would have a material adverse effect on the business, prospects, assets or condition (financial or otherwise) of
the Corporation. 
 (p) Insurance. The Corporation shall (i) maintain insurance with responsible and reputable insurance
companies or associations in such amounts and covering such risks as is customarily carried by similarly situated companies engaged in similar businesses and owning similar properties in the same general areas in which the Corporation operates, but
in any event in amounts sufficient to prevent the Corporation from becoming a co-insurer, and (ii) maintain Directors and Officers liability insurance coverage in form and amounts reasonably acceptable to the Board and customary in the
industry, which coverage names each of the Corporation’s officers and directors as named insureds thereon. 
 (q) Preservation of
Corporate Existence. The Corporation shall preserve and maintain its corporate existence, rights, franchises and privileges in the jurisdiction of its incorporation, and qualify and remain qualified as a foreign corporation in each jurisdiction
in which such qualification is necessary or desirable in view of its business and operations or the ownership or lease of its properties. 

(r) Compliance with Laws. The Corporation shall comply with the requirements of all applicable laws, rules, regulations and orders of
any governmental authority, where noncompliance would have a material adverse effect on the business, operations, affairs, or financial condition of the Corporation. The Corporation shall not (and shall not permit any of its subsidiaries or
affiliates or any of its or their respective directors, officers, managers, employees, independent contractors, representatives or agents to) promise, authorize or make any payment to, or otherwise contribute any item of value to, directly or
indirectly, to any third party, including any Non-U.S. Official (as (as such term is defined in the U.S. Foreign Corrupt Practices Act of 1977, as amended (the “FCPA”)), in each case, in violation of the FCPA, the U.K. Bribery Act,
or any other applicable anti-bribery or anti-corruption law. The Corporation further represents that it shall (and shall cause each of its subsidiaries and affiliates to) cease all of its or their respective activities, as well as remediate any
actions taken by the Corporation, its 

  
 15 

 
subsidiaries or affiliates, or any of their respective directors, officers, managers, employees, independent contractors, representatives or agents in violation of the FCPA, the U.K. Bribery Act,
or any other applicable anti-bribery or anti-corruption law. The Corporation shall promptly notify each Preferred Stockholder if the Corporation becomes aware of any enforcement action pursuant to such laws. The Corporation shall, and
shall cause any direct or indirect subsidiary or entity controlled by it, whether now in existence or formed in the future, to comply with the FCPA. 

(s) Duration of Section. This Section 2 and the rights and obligations of the parties hereunder (other than rights and obligations
set forth in Sections 2(e), (m) and (n) hereof and this Section 2(s)), shall automatically terminate upon the earlier to occur of (i) the consummation of a Qualified Public Offering and (ii) the time at which the
Preferred Stockholders no longer hold any shares of Preferred Stock or Common Stock issued upon conversion of such Preferred Stock. 
 (t)
Capitalization; Additional Purchases. The authorized capital stock of the Corporation immediately after the filing of the Restated Certificate (as defined in the Stock Purchase Agreement) with the secretary of state of the State of Delaware
and prior to the Closing (as defined in the Stock Purchase Agreement) shall be as set forth on Schedule 3 attached hereto. 
 (u)
Right to Conduct Activities. The Corporation hereby agrees and acknowledges that each of the Preferred Stockholders (together with their respective affiliates) is a professional investment fund, or a venture investment arm of its affiliates,
and invests in numerous portfolio companies and has affiliates, some of which may be deemed competitive with the Corporation’s business (as currently conducted or as currently propose to be conducted). The Corporation hereby agrees that,
to the extent permitted under applicable law, none of the Preferred Stockholders shall be liable to the Corporation for any claim arising out of, or based upon, (i) the investment by such Preferred Stockholder in any entity competitive with the
Corporation or the activities of such Preferred Stockholder’s Affiliates, or (ii) actions taken by any partner, officer or other representative of the Preferred Stockholder to assist any such competitive company, whether or not such action
was taken as a member of the board of directors of such competitive company or otherwise, and whether or not such action has a detrimental effect on the Corporation; provided, however, that the foregoing shall not relieve (x) any of the
Preferred Stockholders from liability associated with the unauthorized disclosure of the Corporation’s confidential information obtained pursuant to this Agreement, or (y) any director or officer of the Corporation from any liability
associated with his or her fiduciary duties to the Corporation. 
 3. Transfer of Securities. 

(a) Restriction on Transfer. The Restricted Securities shall not be transferable, except upon the conditions specified in this
Section 3, which conditions are intended solely to ensure compliance with the provisions of the Securities Act in respect of the Transfer thereof. 

  
 16 

 (b) Restrictive Legend. Each certificate evidencing any Restricted Securities and each
certificate evidencing any such securities issued to subsequent transferees of any Restricted Securities shall (unless otherwise permitted by the provisions of Section 3(c) or 3(j) hereof) be stamped or otherwise imprinted with legend in
substantially the following form: 
 THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAW. THE SECURITIES MAY NOT BE PLEDGED, HYPOTHECATED, SOLD OR TRANSFERRED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER THE SECURITIES
ACT OF 1933 OR ANY APPLICABLE STATE SECURITIES LAW OR AN EXEMPTION THEREFROM UNDER SUCH ACT OR LAW. ADDITIONALLY, THE TRANSFER OF THESE SECURITIES IS SUBJECT TO THE CONDITIONS SPECIFIED IN THE STOCKHOLDERS’ AGREEMENT DATED SEPTEMBER 1,
2015, AS AMENDED AND IN EFFECT FROM TIME TO TIME, AMONG PROTEOSTASIS THERAPEUTICS, INC., AND CERTAIN OTHER SIGNATORIES THERETO, AND NO TRANSFER OF SUCH SECURITIES SHALL BE VALID OR EFFECTIVE UNTIL SUCH CONDITIONS HAVE BEEN FULFILLED. COPIES OF SUCH
AGREEMENT MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER OF RECORD OF THIS CERTIFICATE TO THE SECRETARY OF PROTEOSTASIS THERAPEUTICS, INC. 

(c) Notice of Transfer. By acceptance of any Restricted Securities, the holder thereof agrees to give prior written notice to the
Corporation of such holder’s intention to effect any Transfer and to comply in all other respects with the provisions of this Section 3(c). Each such notice shall describe the manner and circumstances of the proposed Transfer and shall be
accompanied by (i) the written opinion of counsel for the holder of such Restricted Securities, or, at such holder’s option, a representation letter of such holder, addressed to the Corporation (which opinion of counsel, or representation
letter, as the case may be, shall be reasonably acceptable to the Corporation), as to whether, in the case of a written opinion, in the opinion of such counsel, such proposed Transfer involves a transaction requiring registration of such Restricted
Securities under the Securities Act and applicable state securities laws or an exemption thereunder is available, or, in the case of a representation letter, such letter sets forth a factual basis for concluding that such proposed transfer involves
a transaction requiring registration of such Restricted Securities under the Securities Act and applicable State securities laws or that an exemption thereunder is available, or (ii) if such registration is required and if the provisions of
Section 3(d) hereof are applicable, a written request addressed to the Corporation by the holder of such Restricted Securities, describing in detail the proposed method of disposition and requesting the Corporation to effect the registration of
such Restricted Securities pursuant to the terms and provisions of Section 3(d) hereof; provided, however, that (x) in the case of a Transfer by a holder to a member of such holder’s Group, no such opinion of counsel or
representation letter of the holder shall be necessary, provided that the transferee agrees in writing to be subject to Sections 3(a), (b), (c), (i), (j), (k) and (l) hereof to the same extent as if such transferee were originally a
signatory hereto, and (y) in the case of any holder of Restricted Securities that is a partnership, no such opinion of counsel or representation letter of the holder 

  
 17 

 
shall be necessary for a Transfer by such holder to a partner of such holder, or a retired partner of such holder who retires after the date hereof, or the estate of any such partner or retired
partner if, with respect to such Transfer by a partnership, (1) such Transfer is made in accordance with the partnership agreement of such partnership and (2) the transferee agrees in writing to be subject to the terms of
Sections 3(a), (b), (c), (i), (j), (k) and (l) hereof to the same extent as if such transferee were originally a signatory hereto. If in such opinion of counsel or as reasonably concluded from the facts set forth in the representation
letter of the holder (which opinion of counsel, or representation letter, as the case may be, shall be reasonably acceptable to the Corporation), the proposed Transfer may be effected without registration under the Securities Act and any applicable
state securities laws or “blue sky” laws, then the holder of Restricted Securities shall thereupon be entitled to effect such Transfer in accordance with the terms of the notice delivered by it to the Corporation. Each certificate or other
instrument evidencing the securities issued upon such Transfer (and each certificate or other instrument evidencing any such securities not Transferred) shall bear the legend set forth in Section 3(b) hereof unless (i) in such opinion of
company counsel or as can be concluded from the representation letter of such holder by company counsel (which opinion and counsel or representation letter shall be reasonably acceptable to the Corporation) the registration of future Transfers is
not required by the applicable provisions of the Securities Act and state securities laws or (ii) the Corporation shall have waived the requirement of such legend; provided, however, that such legend shall not be required on any
certificate or other instrument evidencing the securities issued upon such Transfer in the event such Transfer shall be made in compliance with the requirements of Rule 144 (as amended from time to time, or any similar or successor rule) promulgated
under the Securities Act. The holder of Restricted Securities shall not effect any Transfer until such opinion of counsel or representation letter of such holder has been given to and accepted by the Corporation (unless waived by the Corporation) or
until registration of the Restricted Securities involved in the above-mentioned request has become effective under the Securities Act. In the event that an opinion of counsel is required by the registrar or transfer agent of the Corporation to
effect a transfer of Restricted Securities in the future, the Corporation shall seek and obtain such opinion from its counsel, and the holder of such Restricted Securities shall provide such reasonable assistance as is requested by the Corporation
(other than the furnishing of an opinion of counsel) to satisfy the requirements of the registrar or transfer agent to effectuate such transfer. 

(d) Required Registration. At any time following the date that is the earlier of (i) the fifth anniversary of the date hereof and
(ii) six months following the closing of a Qualified Public Offering, if the Corporation shall be requested by holders of at least two-thirds of the combined voting power of the outstanding Restricted Securities (based on the underlying Common
Stock for which the Restricted Securities are convertible or exercisable) to effect the registration on Form S-1 under the Securities Act of at least 30% of the outstanding Restricted Shares or such
lesser amount of Restricted Shares if the anticipated aggregate offering price would exceed $2,000,000, then the Corporation shall promptly give written notice of such proposed registration to all holders of Restricted Securities, and thereupon the
Corporation shall promptly use its best efforts to effect the registration on Form S-1 under the Securities Act of the Restricted Shares that the Corporation has been requested to register for disposition
as described in the request of such holders of Restricted Securities and in any response received from any of the holders of Restricted Securities within 30 days after the giving of the written notice by the Corporation; provided,
however, that the Corporation shall not be obligated to effect any registration under the Securities Act except in accordance with the following provisions and Section 3(f) hereof. 

  
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 (i) Subject to Section 3(f) hereof, the Corporation shall not be obligated to
file and cause to become effective more than two registration statements in which Restricted Shares are registered under the Securities Act pursuant to this Section 3(d), if all of the Restricted Shares offered pursuant to such registration
statements are sold thereunder upon the price and terms offered or if registration on a Form S-3 is available. Notwithstanding anything in this Section 3 to the contrary, if the Corporation shall furnish to the holders of Restricted Securities who
request registration hereunder a certificate signed by the President or Chief Executive Officer of the Corporation stating that the Board has made the good-faith determination that (i) use or continued use by the holders of the registration
statement filed by the Corporation pursuant to this Section 3 for purposes of effecting offers or sales of Restricted Securities pursuant hereto would require, under the Securities Act and the rules and regulations promulgated thereunder, premature
disclosure in the registration statement (or the prospectus relating thereto) of material, nonpublic information concerning the Corporation, (ii) such premature disclosure would be materially adverse to the Corporation, its business or prospects or
any such proposed material transaction would make the successful consummation by the Corporation of any such material transaction significantly less likely and (iii) it is therefore essential to delay or suspend the use by the holders of such
registration statement (and the prospectus relating thereto) for purposes of effecting offers or sales of Restricted Securities pursuant thereto, then the right of the holders to use such registration statement (and the prospectus relating thereto)
for purposes of effecting offers or sales of Restricted Securities pursuant thereto shall be delayed and/or suspended for a period (the “Suspension Period”) of not more than 90 days after delivery by the Corporation of the
certificate referred to above in this Section 3(d)(i). During the Suspension Period, the Corporation shall not be obligated to file any registration statement and/or the holders shall not offer or sell any Restricted Securities pursuant to or in
reliance upon such registration statement (or the prospectus relating thereto). The Corporation agrees that, as promptly as practicable after the consummation, abandonment or public disclosure of the event or transaction that caused the Corporation
to delay or suspend the use of the registration statement (and the prospectus relating thereto), the Corporation will provide the holders with revised prospectuses, if required, and will notify the Preferred Stockholders of their ability to effect
offers or sales of Registrable Shares pursuant to or in reliance upon such registration statement. The Corporation shall not deliver a certificate causing a Suspension Period more than twice in any twelve (12) month period; provided,
however, that the Suspension Period shall not exceed ninety (90) days in the aggregate in any twelve (12) month period. 

(ii) Notwithstanding the foregoing, the Corporation may include in each such registration requested pursuant to this Section
3(d) any authorized but unissued shares of Common Stock (or authorized treasury shares) for sale by the Corporation or any issued and outstanding shares of Common Stock for sale by others; provided, however, that, if the number of
shares of Common Stock so included pursuant to this clause (ii) exceeds the number of Restricted Shares requested by the holders of Restricted Shares requesting such registration, then such registration shall be deemed to be a registration in
accordance with and pursuant to Section 3(e) hereof; and provided further, however, that the inclusion of such previously authorized but unissued shares by the Corporation or issued and

  
 19 

 
outstanding shares of Common Stock by others in such registration does not adversely affect, in the sole opinion of the holders of Restricted Securities requesting such registration, the ability
of the holders of Restricted Securities requesting such registration to market the entire number of Restricted Shares requested by them. 

(e) Piggyback Registration. 

(i) Each time that the Corporation proposes for any reason to register any of its securities under the Securities Act, other
than pursuant to a registration statement on Form S-4 or Form S-8 or similar or successor forms (collectively, “Excluded Forms”), the Corporation shall promptly give written notice of such proposed registration to all holders of
Restricted Securities, which notice shall offer such holders the right to request inclusion of any Restricted Shares or Common Stock Shares in the proposed registration. 

(ii) Each holder of Restricted Securities shall have 30 days from the receipt of such notice to deliver to the Corporation a
written request specifying the number of Restricted Shares such holder intends to sell and the holder’s intended method of disposition. 

(iii) In the event that the proposed registration by the Corporation is, in whole or in part, an underwritten public offering
of securities of the Corporation, any request under Section 3(e)(ii) hereof may specify that such Restricted Shares be included in the underwriting (A) on the same terms and conditions as the shares of Common Stock, if any, otherwise being
sold through underwriters under such registration or (B) on terms and conditions comparable to those normally applicable to offerings of common stock in reasonably similar circumstances in the event that no shares of Common Stock other than
Restricted Shares are being sold through underwriters under such registration. 
 (iv) Upon receipt of a written request
pursuant to Section 3(e)(ii) hereof, the Corporation shall promptly use its best efforts to cause all such Restricted Shares to be registered under the Securities Act, to the extent required to permit sale or disposition as set forth in the
written request. 
 (v) Notwithstanding the foregoing, if the managing underwriter of any such proposed registration
determines and advises in writing that the inclusion of all Restricted Shares proposed to be included in the underwritten public offering, together with any other issued and outstanding shares of Common Stock proposed to be included therein by
holders other than the holders of Restricted Securities (such other shares hereinafter collectively referred to as the “Other Shares”), would interfere with the successful marketing of the Corporation’s securities, then the
total number of such securities proposed to be included in such underwritten public offering shall be reduced, (A) first, by the shares requested to be included in such registration by the holders of Other Shares and (B) second, if necessary, (I)
one-half by the securities proposed to be issued by the Corporation and (II) one-half by the Restricted Shares proposed to be included in such registration by the holders thereof, on a pro rata basis, based upon the number of
Restricted Shares sought to be registered by each such holder; provided, however, that, except where such proposed underwritten public offering is a Qualified Public Offering, in each of the foregoing cases, holders of Restricted
Securities shall be entitled to include, on a pro rata basis, an aggregate 

  
 20 

 
of such Restricted Shares equal to at least fifty percent (50%) of the total number of securities registered in such proposed underwritten public offering. The shares of Common Stock that
are excluded from the underwritten public offering pursuant to the preceding sentence shall be withheld from the market by the holders thereof for a period, not to exceed 180 days from the closing of such underwritten public offering, that the
managing underwriter reasonably determines as necessary in order to effect such underwritten public offering. 
 (f) Registrations on Form S-3. At such time as the Corporation shall have qualified for the use of Form S-3 (or any successor form promulgated under the Securities Act), each holder of Restricted Securities shall have the right
to request in writing an unlimited number of registrations on Form S-3; provided that (x) the aggregate offering price shall be not less than $1,000,000 and (y) the Corporation shall not be required to effect more than two (2) such
registrations in any 12-month period pursuant to this Section 3(f). Each such request by a holder shall (i) specify the number of Restricted Shares that the holder intends to sell or dispose of and (ii) state the intended method by which the
holder intends to sell or dispose of such Restricted Shares. Upon receipt of a request pursuant to this Section 3(f), the Corporation shall (x) within ten (10) days after the date such request is given by the requesting holder, give notice thereof
to all other holders of Restricted Securities and (y) use its best efforts to effect such registration or registrations on Form S-3. 
 (g)
Preparation and Filing. If and whenever the Corporation is under an obligation pursuant to the provision of this Section 3 to use its best efforts to effect the registration of any Restricted Shares, the Corporation shall, as
expeditiously as practicable: 
 (i) prepare and file with the Commission a registration statement with respect to such
securities and use its best efforts to cause such registration statement to become and remain effective in accordance with Section 3(g)(ii) hereof; 

(ii) prepare and file with the Commission such amendments and supplements to such registration statement and the prospectus
used in connection therewith as may be necessary to keep such registration statement effective until the earlier of (A) the sale of all Restricted Shares covered thereby and (B) nine months, and to comply with the provisions of the
Securities Act with respect to the sale or other disposition of all Restricted Shares covered by such registration statement; 

(iii) furnish to each holder whose Restricted Shares are being registered pursuant to this Section 3 such number of copies
of any summary prospectus or other prospectus, including a preliminary prospectus, in conformity with the requirements of the Securities Act, and such other documents as such holder may reasonably request in order to facilitate the public sale or
other disposition of such Restricted Shares; 
 (iv) use its best efforts to register or qualify the Restricted Shares
covered by such registration statement under the securities or blue sky laws of such jurisdictions as each holder whose Restricted Shares are being registered pursuant to this Section 3 shall reasonably request and do any and all other acts or
things that may be necessary or advisable to enable such holder to consummate the public sale or other disposition in such jurisdictions of such Restricted Shares; provided, however, that the

  
 21 

 
Corporation shall not be required to consent to general service of process for all purposes in any jurisdiction where it is not then subject to process, qualify to do business as a foreign
corporation where it would not be otherwise required to qualify or submit to liability for state or local taxes where it is not otherwise liable for such taxes; 

(v) at any time when a prospectus covered by such registration statement and relating thereto is required to be delivered under
the Securities Act within the appropriate period mentioned in Section 3(g)(ii) hereof, notify each holder whose Restricted Shares are being registered pursuant to this Section 3 of the happening of any event as a result of which the
prospectus included in such registration, as then in effect, includes an untrue statement of a material fact or omits to state a material fact required to be stated therein or necessary to make the statements therein not misleading in light of the
circumstances then existing and, at the request of such holder, prepare, file and furnish to such holder a reasonable number of copies of a supplement to or an amendment of such prospectus as may be necessary so that, as thereafter delivered to the
purchasers of such shares, such prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading in the light of the
circumstances then existing; 
 (vi) if the Corporation has delivered preliminary or final prospectuses to the holders of
Restricted Shares that are being registered pursuant to this Section 3 and after having done so the prospectus is amended to comply with the requirements of the Securities Act, the Corporation shall promptly notify such holders and, if
requested, such holders shall immediately cease making offers of Restricted Shares and return all prospectuses to the Corporation. The Corporation shall promptly provide such holders with revised prospectuses and, following receipt of the revised
prospectuses, such holders shall be free to resume making offers of the Restricted Shares; and 
 (vii) furnish, at the
request of any holder whose Restricted Shares are being registered pursuant to this Section 3, on the date that such Restricted Shares are delivered to the underwriters for sale in connection with a registration pursuant to this Section 3,
if such securities are being sold through underwriters, or, on the date that the registration statement with respect to such securities becomes effective, if such securities are not being sold through underwriters, (A) an opinion, dated such
date, of the counsel representing the Corporation for the purposes of such registration, in form and substance as is customarily given to underwriters in an underwritten public offering and addressed to the underwriters, if any, and to the holder or
holders making such request, and (B) a letter dated such date, from the independent certified public accountants of the Corporation, in form and substance as is customarily given by independent certified public accountants to underwriters in an
underwritten public offering, addressed to the underwriters, if any, and to the holder or holders making such request. 
 (h)
Expenses. The Corporation shall pay all expenses incurred by the Corporation in complying with this Section 3, including, without limitation, all registration and filing fees (including all expenses incident to filing with the National
Association of Securities Dealers, Inc.), fees and expenses of complying with the securities and blue sky laws of all such jurisdictions in which Restricted Shares are proposed to be offered and sold, printing expenses and fees and disbursements of
counsel (including, with respect to each registration effected 

  
 22 

 
pursuant to Section 3(d), (e) or (f) hereof, the fees and disbursements of one special counsel for the holders of Restricted Shares that are being registered pursuant to this Section 3, up to a
maximum of $25,000 per registration); provided, however, that all underwriting discounts and selling commissions applicable to the Restricted Shares covered by registrations effected pursuant to Section 3(d), 3(e) or 3(f) hereof shall
be borne by the seller or sellers thereof, in proportion to the number of Restricted Shares sold by each such seller or sellers. 
 (i)
Indemnification. 
 (i) In the event of any registration of any Restricted Shares under the Securities Act pursuant to
this Section 3 or registration or qualification of any Restricted Shares pursuant to Section 3(g)(iv) hereof, the Corporation shall indemnify and hold harmless the seller of such shares, each underwriter of such shares, if any, each broker or any
other person acting on behalf of such seller and each other person, if any, who controls (within the meaning of the Securities Act, the Exchange Act or any state securities or blue-sky laws) any of the foregoing persons against any losses, claims,
damages or liabilities, joint or several, to which any of the foregoing persons may become subject under the Securities Act, the Exchange Act or any state securities or blue-sky laws or otherwise, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon an untrue statement or alleged untrue statement of a material fact contained in any registration statement under which such Restricted Shares were registered under the
Securities Act, any preliminary prospectus or final prospectus contained therein, or any amendment or supplement thereto, or any document incident to registration or qualification of any Restricted Shares pursuant to Section 3(g)(iv) hereof, or
arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading or, with respect to any prospectus, necessary to make the
statements therein, in light of the circumstances under which they were made, not misleading, or any violation by the Corporation of the Securities Act, the Exchange Act or any state securities or blue sky laws applicable to the Corporation and
relating to action or inaction required of the Corporation in connection with such registration or qualification under the Securities Act, the Exchange Act or such state securities or blue-sky laws. The Corporation shall reimburse on demand such
seller, underwriter, broker or other person acting on behalf of such seller and each such controlling person for any legal or any other expenses reasonably incurred by any of them in connection with investigating or defending any such loss, claim,
damage, liability or action; provided, however, that the Corporation shall not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission made in said registration statement, preliminary or final prospectus or amendment or supplement thereto or any document incident to registration or qualification of any Restricted Shares pursuant to
Section 3(g) hereof, in reliance upon and in conformity with written information furnished to the Corporation by such seller, underwriter, broker, other person or controlling person specifically for use in the preparation thereof. 

(ii) Before Restricted Shares held by any prospective seller shall be included in any registration pursuant to this
Section 3, such prospective seller and any underwriter acting on its behalf shall have agreed to indemnify and hold harmless (in the same manner and to the same extent as set forth in Section 3(i)(i) hereof) the Corporation,

  
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each director of the Corporation, each officer of the Corporation who signs such registration statement and any person who controls the Corporation within the meaning of the Securities Act, with
respect to any untrue statement or omission from such registration statement, any preliminary prospectus or final prospectus contained therein, or any amendment or supplement thereto, if such untrue statement or omission was made in reliance upon
and in conformity with written information furnished to the Corporation through an instrument duly executed by such seller or such underwriter specifically for use in the preparation of such registration statement, preliminary prospectus, final
prospectus or amendment or supplement; provided, however, that the maximum amount of liability in respect of such indemnification shall be limited, in the case of each prospective seller, to an amount equal to the net proceeds actually
received by such prospective seller from the sale of Restricted Shares effected pursuant to such registration. 
 (iii)
Promptly after receipt by an indemnified party of notice of the commencement of any action involving a claim referred to in Section 3(i)(i) or (ii) hereof, such indemnified party will, if a claim in respect thereof is to be made against the
indemnifying party under this Section 3(i), give written notice to the latter of the commencement of such action. In case any such action is brought against an indemnified party, the indemnifying party will be entitled to participate in and to
assume the defense thereof, jointly with any other indemnifying party similarly notified to the extent that it may wish, with counsel reasonably satisfactory to such indemnified party, and, after notice to such indemnified party from the
indemnifying party of its election to assume the defense thereof, the indemnifying party shall be responsible for any legal or other expenses subsequently incurred by the latter in connection with the defense thereof; provided,
however, that, if any indemnified party shall have reasonably concluded that there may be one or more legal defenses available to such indemnified party that are different from or additional to those available to the indemnifying party, or
that such claim or litigation involves or could have an effect upon matters beyond the scope of the indemnity agreement provided in this Section 3(i), the indemnifying party shall not have the right to assume the defense of such action on behalf of
such indemnified party, and such indemnifying party shall reimburse such indemnified party and any person controlling such indemnified party for the fees and expenses of counsel retained by the indemnified party that are reasonably related to the
matters covered by the indemnity agreement provided in this Section 3(i). The indemnifying party shall not make any settlement of any claims indemnified against hereunder without the written consent of the indemnified party or parties, which consent
shall not be unreasonably withheld. 
 (iv) In order to provide for just and equitable contribution to joint liability under
the Securities Act in any case in which either (A) any holder of Restricted Shares exercising rights hereunder, or any controlling person of any such holder, makes a claim for indemnification pursuant to this Section 3(i), but it is judicially
determined (by the entry of a final judgment or decree by a court of competent jurisdiction and the expiration of time to appeal or the denial of the last right of appeal) that such indemnification may not be enforced in such case notwithstanding
the fact that this Section 3(i) provides for indemnification in such case, or (B) contribution under the Securities Act may be required on the part of any such holder or any such controlling person in circumstances for which indemnification is
provided under this Section 3(i), then, in each such case, the Corporation and such holder will contribute to the aggregate losses, 

  
 24 

 
claims, damages or liabilities to which they may be subject as is appropriate to reflect the relative fault of the Corporation and such holder in connection with the statements or omissions that
resulted in such losses, claims, damages or liabilities, it being understood that the parties acknowledge that the overriding equitable consideration to be given effect in connection with this provision is the ability of one party or the other to
correct the statement or omission that resulted in such losses, claims, damages or liabilities, and that it would not be just and equitable if contribution pursuant hereto were to be determined by pro rata allocation or by any other
method of allocation that does not take into consideration the foregoing equitable considerations. Notwithstanding the foregoing, (x) no such holder will be required to contribute any amount in excess of the proceeds to it of all Restricted
Shares sold by it pursuant to such registration statement and (y) no person or entity guilty of fraudulent misrepresentation, within the meaning of Section 11(f) of the Securities Act, shall be entitled to contribution from any person or
entity who is not guilty of such fraudulent misrepresentation. 
 (v) Notwithstanding any of the foregoing, if, in connection
with an underwritten public offering of any Restricted Shares, the Corporation, the holders of such Restricted Shares and the underwriters enter into an underwriting or purchase agreement relating to such offering that contains provisions covering
indemnification among the parties, then the indemnification provision of this Section 3(i) shall be deemed inoperative for purposes of such offering. 

(j) Removal of Legends, etc. Notwithstanding the foregoing provisions of this Section 3, the restrictions imposed by this
Section 3 upon the transferability of any Restricted Securities shall cease and terminate when (i) any such Restricted Securities are sold or otherwise disposed of in accordance with the intended method of disposition by the seller or
sellers thereof set forth in a registration statement or such other method contemplated by Section 3(c) hereof that does not require that the securities transferred bear the legend set forth in Section 3(b) hereof, including a Transfer
pursuant to Rule 144 or a successor rule thereof (as amended from time to time), or (ii) the holder of Restricted Securities has met the requirements for transfer of such Restricted Securities pursuant to Rule 144(b)(1) or a successor rule
thereof (as amended from time to time) promulgated by the Commission under the Securities Act. Whenever the restrictions imposed by this Section 3 have terminated, a holder of a certificate for Restricted Securities as to which such
restrictions have terminated shall be entitled to receive from the Corporation, without expense, a new certificate not bearing the restrictive legend set forth in Section 3(b) hereof and not containing any other reference to the restrictions
imposed by this Section 3. 
 (k) Lockup. Each holder of Restricted Securities and each Common Stockholder hereby agrees that,
at the written request of any managing underwriter of an underwritten initial public offering that is a Qualified Public Offering of securities of the Corporation, each such holder and Common Stockholder shall not, without the prior written consent
of such managing underwriter, sell, assign, transfer, make a short sale of, loan, grant any option for the purchase of, pledge, hypothecate, encumber or otherwise convey or dispose of, or exercise registration rights with respect to any securities
for such period of time, not to exceed 180 days after the closing of such underwritten initial public offering, as the Corporation or such managing underwriter shall request. Without limiting the generality of the foregoing provisions of this
Section 3(k) in connection with any Qualified Public Offering of securities of the 

  
 25 

 
Corporation, no holder of Restricted Securities or Common Stockholder shall be obligated to enter into any lock-up agreement requested by the managing underwriter unless all other stockholders,
directors and executive officers of the Corporation are being required to enter into a lock-up agreement with similar, or more restrictive, terms. 

(l) Assignment of Registration Rights. The rights of the holders of Restricted Securities under this Section 3 may be assigned
(but only with all related obligations) by a holder of Restricted Securities to a transferee or assignee of such securities who, after such assignment or transfer, (i) holds at least 1,000,000 shares of Restricted Securities (subject to
proportionate adjustment in the event of any stock dividend, stock split, combination of shares, reorganization, recapitalization, reclassification or other similar event affecting Restricted Securities and occurring after the date hereof),
(ii) holds, together with the affiliates of such transferee or assignee, all of the Restricted Securities held by the transferring holder immediately prior to such transfer or (iii) who is an affiliate, partner or member of such holder
including, without limitation, with respect to any holder that is a Preferred Stockholder, any member of such Preferred Stockholder’s Group; provided that the Corporation is furnished with written notice of the name and address of such
transferee or assignee and the securities with respect to such assignment shall be effective only if (x) immediately following such transfer the further disposition of such Restricted Securities by the transferee or assignee is restricted under
the Securities Act and (y) unless the transferee or assignee is a member of a Group, such transferee or assignee shall acknowledge in writing that the transferred or assigned Restricted Securities shall remain subject hereto. For the purposes
of determining the number of shares of Restricted Securities held by a transferee or assignee, the holdings of transferees and assignees of a partnership who are partners or retired partners of such partnership (including spouses and ancestors,
lineal descendants and siblings of such partners or spouses who acquire Restricted Securities by gift, will or intestate succession) shall be aggregated together and with the partnership. 

(m) Bring-Along Rights. 

(i) If, by vote or written consent, (A) the Board and (B) the holders of at least two-thirds of the then-outstanding
shares of Preferred Stock, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by such holders) (the “Approving Preferred
Stockholders”), approve a change of control of the Corporation pursuant to which any bona fide unaffiliated third party proposes to acquire all or substantially all of the assets or two-thirds or more of the then-outstanding capital stock
of the Corporation, whether by purchase, merger, consolidation, share exchange, sale of assets, exclusive license or otherwise (an “Approved Sale”), the Approving Preferred Stockholders shall provide all other holders of Preferred
Stock who are not Approving Preferred Stockholders and each Common Stockholder (collectively, the “Remaining Stockholders”) at least 15 days’ advance notice of such Approved Sale, which notice shall include a reasonably
detailed description of the Approved Sale, including the proposed time and place of closing, the consideration to be received by the Remaining Stockholders, and any other material terms. The Remaining Stockholders shall consent to, vote for and
raise no objections to the Approved Sale, and (x) the Remaining Stockholders shall waive any dissenters rights, appraisal rights or similar rights, if any, in connection with such merger, consolidation or asset sale or (y) if the Approved
Sale is structured as a sale of the stock of the Corporation, 

  
 26 

 
the Remaining Stockholders shall agree to sell all of their shares of capital stock on the terms and conditions approved by the Approving Preferred Stockholders to the extent consistent with the
liquidation preferences as set forth in the Certificate as if such sale were a Liquidation Event thereunder. The Remaining Stockholders shall take all reasonably necessary and desirable actions requested by the Approving Preferred Stockholders in
connection with the consummation of the Approved Sale, including the execution of such agreements and such instruments (collectively, the “Sale Documents”) and other actions reasonably necessary to (1) effectuate the Approved
Sale, including (only in the case that a third party requires both the Corporation and all of the Approving Preferred Stockholders and the Remaining Stockholders to individually sign such Sale Documents) making such customary representations,
warranties, indemnities, covenants, conditions, escrow agreements and other customary agreements relating to such Approved Sale (subject to the provisions of subsection (ii) below) and (2) effectuate the agreed-upon allocation and
distribution of the aggregate consideration upon the Approved Sale. 
 (ii) Notwithstanding the foregoing, a Remaining
Stockholder will not be required to comply with Section 3(m)(i) above in connection with any Approved Sale, unless: 

(a) any representations and warranties to be made by such Remaining Stockholder in connection with such Approved Sale are
limited to representations and warranties related to authority, ownership, the ability to convey title to shares owned by such Remaining Stockholder, or otherwise pertaining to such Remaining Stockholder and not the operations of the Corporation;

 (b) such Remaining Stockholder (i) shall not be liable for the inaccuracy of any representation or warranty made by
any other Person in connection with such Approved Sale; (ii) shall only be liable jointly on a pro rata basis (in proportion to the amount of consideration paid to such Remaining Stockholder in such Approved Sale), and not jointly and
severally, for the inaccuracy of any representations and warranties made by the Corporation in connection with such Approved Sale, in the case of (i) and (ii) except to the extent that funds may be paid out of an escrow established to
cover breaches of representations, warranties and covenants of the Corporation and/or breaches by any Remaining Stockholder or Approving Preferred Stockholder of any representations, warranties and covenants provided by all Remaining Stockholders or
Approving Preferred Stockholders; and (iii) shall not be liable for any amount in excess of the amount of consideration otherwise payable to such Remaining Stockholder in connection with such Approved Sale, except with respect to claims related
to fraud or intentional breach by such Remaining Stockholder, the liability for which need not be limited as to such Remaining Stockholder; and 

(c) upon the consummation of the Approved Sale (i) each holder of each class or series of the Corporation’s stock
will receive the same form of consideration for their shares of such class or series as is received by other holders in respect of their shares of such same class or series of stock; (ii)

  
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each holder of each class or series of the Corporation’s stock will receive the same amount of consideration per share of such class or series as is received by other holders in respect of
their shares of such same class or series; and (iii) the aggregate consideration receivable by Remaining Stockholders is not less than the amount that would be distributed to such Remaining Stockholders in the event the proceeds of the Approved
Sale were distributed in accordance with the Certificate. 
 (iii) Each of the Remaining Stockholders hereby appoints the
Approving Preferred Stockholder holding the largest number of shares of the Preferred Stock, for so long as the provisions of Section 3(m)(i) hereof remain in effect, as such Remaining Stockholder’s attorney and proxy with full power of
substitution, to vote, and otherwise act (by written consent or otherwise) with respect to the capital stock of the Corporation owned by such Remaining Stockholder, solely on the matters and in the manner specified in Section 3(m)(i) hereof,
but if and only if such Remaining Stockholder (A) fails to vote or (B) attempts to vote (whether by proxy, in person or by written consent) in a manner that is inconsistent with the provisions of such Section 3(m)(i). 

(iv) THE PROXIES AND POWER OF ATTORNEY GRANTED PURSUANT TO THE ABOVE PARAGRAPH ARE IRREVOCABLE AND COUPLED WITH AN INTEREST.
All authority herein conferred or agreed to be conferred shall survive the death or incapacity of each Remaining Stockholder and any obligation of a Remaining Stockholder hereunder shall be binding upon the heirs, personal representatives and
successors of such Remaining Stockholder. 
 (v) Each Stockholder agrees that it will not, nor will it permit any entity
under its control to, deposit any of the Restricted Securities in a voting trust or subject any of the Restricted Securities to any arrangement or agreement with respect to the voting of the Restricted Securities inconsistent herewith. In addition,
each Stockholder shall not transfer any of the Restricted Securities unless, as a condition precedent thereto, each transferee of such Restricted Securities shall explicitly agree to execute and deliver, and be bound by, the terms hereof, including
this Section 3(m) and Section 5(a) below. Each Stockholder acknowledges that it will be impossible to measure in money the damages to the Corporation if such Stockholder fails to comply with the obligations imposed by this
Section 3(m) and Section 5(a) below and that, in the event of any such failure, the Corporation will not have an adequate remedy at law or in damages. Accordingly, each Stockholder and the Corporation agree that injunctive relief or other
equitable remedy, in addition to remedies at law or damages, is the appropriate remedy for any such failure and will not oppose the granting of such relief on the basis that the Corporation has an adequate remedy at law. 

4. Securities Act Registration Statements. Except for securities of the Corporation registered on Excluded Forms, the Corporation shall
not file any registration statement under the Securities Act covering any securities unless it shall first have given each holder of Restricted Securities written notice thereof. The Corporation further covenants that each holder of Restricted
Securities shall have the right, at any time when it may be deemed to be a controlling person of the Corporation, within the meaning of the Securities Act, to participate in the 

  
 28 

 
preparation of such registration statement and to request the insertion therein of material furnished to the Corporation in writing that, in such holder’s judgment, should be included. In
connection with any registration statement referred to in this Section 4, the Corporation shall indemnify, to the extent permitted by law, each holder of Restricted Securities, its officers, partners and directors and each person, if any, who
controls any such holder within the meaning of the Securities Act in the same manner and to the same extent as the Corporation is required to indemnify a seller of Restricted Securities in Section 3(i) hereof. If, in connection with any such
registration statement, any holder of Restricted Securities shall furnish written information to the Corporation expressly for use in the registration statement, then such holder shall indemnify the Corporation, each director of the Corporation,
each officer of the Corporation who signs such registration statement and each person, if any, who controls the Corporation within the meaning of the Securities Act to the same extent as a seller of Restricted Securities is required to indemnify
such persons in Section 3(i) hereof. 
 5. Directors; Observers and Committees. 

(a) Voting for Directors. At each annual meeting of the stockholders of the Corporation and at each special meeting of the stockholders
of the Corporation called for the purposes of electing directors of the Corporation, and at any time at which stockholders of the Corporation shall have the right to, or shall, vote for or consent to the election of directors, then, in each such
event, each Common Stockholder, each Series A Holder, each Series B Holder and each other signatory hereto shall vote all shares of voting stock of the Corporation then owned (or controlled as to voting rights) by it, him or her, whether by
purchase, exercise of rights, warrants or options, stock dividends or otherwise: 
 (i) to fix and maintain the number of
directors on the Board at no more than eleven (11); 
 (ii) to elect to the Board six (6) directors designated as
follows: 
 (A) one person designated by HCV Group; 

(B) one person designated by Fidelity Group; 

(C) one person designated by Genzyme Corporation; 

(D) one person designated by New Enterprise Associates 12, Limited Partnership; 

(E) one person designated by Novartis BioVentures Ltd.; and 

(F) one person designated by Elan. 

each of which directors identified in this clause (ii) being the Series A Directors as defined in Section A.6(b) of Article III of the
Certificate; 
 (iii) to elect to the Board one (1) director designated by the Principal Stockholders; 

  
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 (iv) to elect to the Board one (1) director who shall be the Chief Executive
Officer of the Corporation; 
 (v) to elect to the Board two (2) independent directors designated by a majority of other
Board members, one of whom shall initially be Christopher T. Walsh. 
 (b) Powers. The management of the business and conduct of the
affairs of the Corporation shall be vested in the Board. Without limiting the foregoing, the Corporation shall not take any of the following actions without the approval of the Board (including a majority of the Series A Directors): 

(i) sell, abandon, transfer, lease or otherwise dispose of all or substantially all of the Corporation’s or any of its
subsidiary’s assets or properties; 
 (ii) purchase, lease or otherwise acquire all or substantially all of the assets
of another entity; 
 (iii) except as otherwise required by the Certificate, declare or pay any dividend or make any
distribution shares of capital stock or securities of the Corporation (whether in cash, shares of capital stock or other securities or property); 

(iv) except as otherwise required by the Certificate, make any payment (in cash or any other property) on account of the
purchase, redemption or other retirement of any share of capital stock of the Corporation or any subsidiary, or distribute to Common Stockholders shares of the Corporation’s capital stock (other than Common Stock) or other securities of other
entities, evidences of indebtedness issued by the Corporation or other entities, or other assets or options or rights (excluding options to purchase and rights to subscribe for shares of Common Stock or the securities of the Corporation convertible
into or exchangeable for shares of Common Stock) other than the repurchase of shares of Common Stock issued pursuant to any equity incentive plan of the Corporation for terminated employees or consultants but not Common Stockholders or under a stock
restriction agreement that (A) is approved by the Board (including the approval of a majority of the Series A Directors) (B) does not exceed $100,000 in the aggregate in any 12-month period and (C) is not payable when there is
any default under the Corporation’s obligations pursuant to Section A.5(a) of Article III of the Certificate; or on other terms approved by the Board (including the approval of a majority of the Series A Directors); 

(v) merge or consolidate with or into or permit any subsidiary to merge or consolidate with or into any other corporation or
corporations or other entity or entities; 
 (vi) voluntarily dissolve, liquidate, wind-up or carry out any partial
Liquidation (as defined in Section A.4(b) of Article III of the Certificate) or distribution or transaction in the nature of a partial Liquidation or distribution; 

(vii) alter or change the designations, powers, preferences or rights of the Series A Preferred Stock of the Corporation;

 (viii) amend, alter or repeal any of the provisions of the certificate of incorporation or the bylaws of the Corporation
or any of its subsidiaries; 

  
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 (ix) except for the issuance of capital stock or other securities constituting
shares of Excluded Stock (as defined in Section A.7(d)(ii) of Article III of the Certificate), authorize, designate, reclassify, create, issue or agree to issue any equity or debt security of the Corporation or any of its subsidiaries, or
any security, right, option or warrant convertible into, or exercisable or exchangeable for, shares of the capital stock of the Corporation or any capitalized lease with an equity feature with respect to the capital stock of the Corporation (except
that the approval of the Series A Directors shall not be required for the issuance of Excluded Stock); 
 (x) adopt,
approve, amend or modify (except for immaterial changes) any stock option plan, stock option agreement, restricted stock purchase agreement or stock restriction agreement entered into between the Corporation and its employees, officers, directors,
consultants and/or independent contractors; 
 (xi) accelerate the vesting schedule or exercise date of any such options or
in any such stock option agreement, restricted stock purchase agreement or stock restriction agreement or waive or modify the Corporation’s repurchase rights with respect to any shares of the Corporation’s stock issuable pursuant to any
restricted stock purchase agreement, stock option agreement or stock restriction agreement; 
 (xii) grant any stock options
with an exercise price per share that is less than the fair market value of such share on the date of such grant (as determined by the Board) or issue or sell capital stock of the Corporation pursuant to restricted stock awards or restricted stock
purchase agreements at a price per share less than the fair market value of such share on the date of such issuance or sale (as determined by the Board); 

(xiii) enter into any financing arrangement in excess of $50,000 including, without limitation, loan agreements, credit lines,
letters of credit, capitalized leases or any capital expenditure; 
 (xiv) enter into any contract, agreement or license or
series of related contracts, agreements or licenses in excess of $50,000, whether in a single disbursement or a series of related disbursements, or for a term in excess of 12 months; 

(xv) enter into or become subject to any agreement that restricts or purports to restrict the Corporation from engaging or
otherwise competing in any material aspect of its business anywhere in the world or that otherwise limits the business in which the Corporation may engage or compete; 

(xvi) take any action or enter into any other transaction outside the ordinary course of business or effect any material change
in the conduct or operation of the Corporation’s business; 
 (xvii) participate or allow any subsidiary to participate
in any line of business other than the line of business described in the Business Plan attached to the Stock Purchase Agreement; 

(xviii) appoint, terminate or remove the Chief Executive Officer or President or the Chief Financial Officer, Treasurer or Vice
President-Finance; 

  
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 (xix) adjust the compensation of key management personnel; 

(xx) make any loans or guarantees; 

(xxi) sell, transfer, license or any disposition of any intellectual property rights of the Corporation; 

(xxii) adopt the annual budget of the Corporation; 

(xxiii) incur any indebtedness by the Corporation or any subsidiary in excess of $50,000; or 

(xxiv) enter into any transactions with affiliates of the Corporation. 

(c) Proxy. Each Stockholder hereby grants to the other holders of shares of Preferred Stock an irrevocable proxy, coupled with an
interest, to vote, as a majority in interest of the Preferred Stock held by such other holders, all shares of voting capital stock of the Corporation held by such Stockholder (and any other shares of such stock over which he, she or it exercised
voting control) and to take such other action to the extent necessary to carry out the provisions of Section 5(a), but if and only if such Stockholder (i) fails to vote or (ii) attempts to vote (whether by proxy, in person or by
written consent) in a manner that is inconsistent with the provisions of Section 5(a). THE PROXIES AND POWER OF ATTORNEY GRANTED PURSUANT TO THIS PARAGRAPH ARE IRREVOCABLE AND COUPLED WITH AN INTEREST. 

(d) Cooperation of the Corporation. The Corporation shall use its best efforts to effectuate the purposes of this Section 5,
including promoting the adoption of any necessary amendment of the bylaws of the Corporation and the Certificate. 
 (e) Notices. The
Corporation shall provide the Preferred Stockholders with at least 20 days’ prior notice in writing of any intended mailing of notice to the Preferred Stockholders of the Corporation for a meeting at which directors are to be elected, and such
notice shall include the names of the persons designated by the Corporation pursuant to this Section 5. Each Preferred Stockholder with board-member-designation rights pursuant to Section 5(a)(ii) hereof shall notify the Corporation in
writing at least three days prior to such mailing of the persons designated by them respectively pursuant to Section A.6(b) of Article III of the Certificate and Section 5(a)(ii) hereof as nominees for election to the Board. In the
absence of any notice from such Preferred Stockholder, the director(s) then serving and previously designated by such Preferred Stockholder shall be re-nominated. 

(f) Removal. Except as otherwise provided in this Section 5, no Preferred Stockholder or Common Stockholder shall vote to remove
any member of the Board designated in accordance with the foregoing provisions of this Section 5 unless the party who designated such director (the “Designating Party”) shall so vote or otherwise consent, and, if the
Designating Party shall so vote or otherwise consent, then the non-designating Preferred Stockholders or Common Stockholders shall likewise so vote. Any vacancy on the Board created by the resignation, removal, incapacity or death of any person
designated under the foregoing provisions of this Section 5 shall be filled by another person designated by the original Designating Party. Each Preferred Stockholder and Common Stockholder shall vote all shares of

  
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voting stock of the Corporation owned or controlled by such Preferred Stockholder or Common Stockholder, respectively, in accordance with each such new designation, and no such vacancy shall be
filled in the absence of a new designation by the original Designating Party. 
 (g) Duration of Section. This Section 5 and the
rights and obligations of the parties hereunder shall automatically terminate on the consummation of a Qualified Public Offering. The rights and obligations of any Preferred Stockholder under this Section 5 other than the obligations of such
Preferred Stockholder under Section 5(a) hereof shall terminate upon the date on which such Preferred Stockholder (together with all members of such Preferred Stockholder’s Group) no longer owns twenty-five percent (25%) of the shares
of Preferred Stock issued to such Designating Party pursuant to the Stock Purchase Agreement, whereupon the obligations of the remaining Preferred Stockholder and the Common Stockholders to vote in favor of the designee of such Preferred Stockholder
shall also terminate. 
 (h) “Bad Actor” Matters. 

(i) Representation. Each Preferred Stockholder with the right to designate or participate in the designation of a director pursuant to
this Agreement hereby represents that no Disqualification Event is applicable to such Preferred Stockholder or any of its Rule 506(d) Related Parties, except, if applicable, for a Disqualification Event as to which Rule 506(d)(2)(ii) or
(iii) or (d)(3) is applicable. For purposes of this Agreement, “Rule 506(d) Related Party” shall mean with respect to any Person any other Person that is a beneficial owner of such first Person’s securities for purposes of
Rule 506(d) of the Securities Act. 
 (ii) Covenant. Each Preferred Stockholder with the right to designate or participate in the
designation of a director pursuant to this Agreement hereby agrees that it shall notify the Corporation promptly in writing in the event a Disqualification Event becomes applicable to such Preferred Stockholder or any of its Rule 506(d) Related
Parties, except, if applicable, for a Disqualification Event as to which Rule 506(d)(2)(ii) or (iii) or (d)(3) is applicable. 
 6.
Indemnification. 
 (a) Indemnification of Preferred Stockholders. In the event that any Preferred Stockholder or any
director, officer, employee, affiliate or agent thereof (the “Indemnitees”) becomes involved in any capacity in any action, proceeding, investigation or inquiry in connection with or arising out of any matter related to the
Corporation or any Indemnitee’s role or position with the Corporation, the Corporation shall reimburse each Indemnitee for its legal and other expenses (including the cost of any investigation and preparation) as they are incurred by such
Indemnitee in connection therewith; provided, however, that the Corporation shall not be obligated to indemnify any Indemnitee found by a court of final jurisdiction (i) to have acted with willful misconduct in connection with the
matter, (ii) to have breached this Agreement and (iii) to have failed to comply with the law. The Corporation also agrees to indemnify each Indemnitee, pay on demand and protect, defend, save and hold harmless from and against any and all
liabilities, damages, losses, settlements, claims, actions, suits, penalties, fines, costs or expenses (including, without limitation, attorneys’ fees) (any of the foregoing, a “Claim”) incurred by or asserted against any Indemnitee
of whatever kind or nature, arising from, in connection with or occurring as a result hereof or the matters contemplated hereby. The foregoing agreement shall be in addition to any rights that any Indemnitee may have at common law or otherwise. 

  
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 (b) Advancement of Expenses. The Corporation shall advance all expenses reasonably
incurred by or on behalf of the Indemnitees in connection with any Claim or potential Claim within twenty (20) days after the receipt by the Corporation of a statement or statements from the Indemnitee requesting such advance payment or
payments from time to time. 
 (c) No Contribution from Preferred Stock Indemnitors. The Corporation hereby acknowledges that
Indemnitees have certain rights to indemnification, advancement of expenses and insurance provided by the Preferred Stockholders and certain of their affiliates (collectively, the “Preferred Stock Indemnitors”). The
Corporation hereby agrees that (i) it is the indemnitor of first resort (i.e., its obligations to the Indemnitees are primary and any obligation of the Preferred Stock Indemnitors to advance expenses or to provide indemnification for the same
expenses or liabilities incurred by any Indemnitee are secondary), (ii) it shall be required to advance the full amount of expenses incurred by any Indemnitee and shall be liable for the full amount of all expenses, judgments, penalties, fines
and amounts paid in settlement to the extent legally permitted and as required by the terms of this Agreement and the Certificate or bylaws of the Corporation (or any other agreement between the Corporation and the Indemnitees), without regard to
any rights any Indemnitee may have against the Preferred Stock Indemnitors, and (iii) it irrevocably waives, relinquishes and releases the Preferred Stock Indemnitors from any and all claims against the Preferred Stock Indemnitors for
contribution, subrogation or any other recovery of any kind in respect thereof. The Corporation further agrees that (x) no advancement or payment by the Preferred Stock Indemnitors on behalf of any Indemnitee with respect to any claim for which
any Indemnitee has sought indemnification from the Corporation shall affect the foregoing and (y) the Preferred Stock Indemnitors shall have a right of contribution and/or be subrogated to the extent of such advancement or payment to all of the
rights of recovery of such Indemnitee against the Corporation. The Corporation and the Indemnitees agree that the Preferred Stock Indemnitors are express third-party beneficiaries of the terms of this Section 6(c). 

(d) Subrogation. Except as provided in Section 6(c) hereof, in the event of any payment hereunder, the Corporation shall be
subrogated to the extent of such payment to all of the rights of recovery of any Indemnitee (other than against the Preferred Stock Indemnitors), who shall execute all papers required and take all action necessary to secure such rights, including
execution of such documents as are necessary to enable the Corporation to bring suit to enforce such rights. 
 (e) Director
Indemnification. The Corporation and the Stockholders agree not to take any action to amend any provision of the Certificate or the bylaws of the Corporation relating to indemnification of directors, as presently in effect, without the prior
written consent of the holders of at least two-thirds of the then-outstanding Preferred Stock, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares
held by such holders). 
 7. Remedies. In case any one or more of the covenants and/or agreements set forth herein shall have been
breached by any party hereto, the party or parties entitled to the benefit of such covenants or agreements may proceed to protect and enforce its or their rights, either by suit 

  
 34 

 
in equity and/or action at law, including, but not limited to, an action for damages as a result of any such breach and/or an action for specific performance of any such covenant or agreement
contained herein. The rights, powers and remedies of the parties hereunder are cumulative and not exclusive of any other right, power or remedy that such parties may have under any other agreement or law. No single or partial assertion or exercise
of any right, power or remedy of a party hereunder shall preclude any other or further assertion or exercise thereof. 
 8. Successors
and Assigns. Except as otherwise expressly provided herein, this Agreement shall bind and inure to the benefit of the Corporation and each of the Preferred Stockholders and the respective successors and permitted assigns of the Corporation and
each of the Preferred Stockholders (including any member of a Preferred Stockholder’s Group). Subject to the requirements of Section 3 hereof, this Agreement and the rights and duties of the Preferred Stockholders set forth herein may be
freely assigned, in whole or in part, by each Preferred Stockholder to any member of such Preferred Stockholder’s Group. Any transferee (other than a Preferred Stockholder) to whom rights under Section 3 hereof are transferred by a
Preferred Stockholder shall, as a condition to such transfer, deliver to the Corporation a written instrument by which such transferee identifies itself, gives the Corporation notice of the transfer of such rights, identifies the securities of the
Corporation owned or acquired by it and agrees to be bound by the obligations imposed hereunder to the same extent as if such transferee were a Preferred Stockholder hereunder. A transferee to whom rights are transferred by a Preferred Stockholder
pursuant to this Section 8 will be thereafter deemed to be a Preferred Stockholder for the purpose of the execution of such transferred rights and may not again transfer such rights to any other person or entity, other than as provided in this
Section 8. Neither this Agreement nor any of the rights or duties of the Corporation set forth herein shall be assigned by the Corporation, in whole or in part, without having first received the written consent of the Preferred Stockholders
(including any members of a Preferred Stockholder’s Group) holding two-thirds in voting power of the outstanding Preferred Stock, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such
calculation any outstanding Restricted Shares held by such holders). 
 9. Duration of Agreement. The rights and obligations of the
Corporation, the Common Stockholders and each Preferred Stockholders set forth herein shall survive indefinitely, unless and until, by their respective terms, they are no longer applicable. 

10. Entire Agreement. This Agreement, together with the other writings referred to herein or delivered pursuant hereto that form a part
hereof, contains the entire agreement among the parties with respect to the subject matter hereof and amends, restates and supersedes all prior and contemporaneous arrangements or understandings with respect thereto. Without limiting the generality
of the foregoing, this Agreement amends and restates the Prior Agreement in its entirety. 
 11. Notices. All notices, requests,
consents and other communications hereunder to any party shall be deemed to be sufficient if contained in a written instrument delivered in person or duly sent by first class registered, certified or overnight mail, postage prepaid, or facsimile
with a confirmation copy by regular mail, addressed or faxed, as the case may be, to such party at the address or facsimile number, as the case may be, set forth below or such other address or facsimile number, as the case may be, as may hereafter
be designated in writing by the addressee to the addressor listing all parties: 
 (a) if to the Corporation, to: 

Proteostasis Therapeutics, Inc. 

200 Technology Square, Suite 402 

Cambridge, MA 02139 

  
 35 

 with a copy to: 

Goodwin Procter LLP 
 53 State
Street 
 Boston, MA 02109 

Attention: Mitchell S. Bloom and John M. Mutkoski 

Fax: (617) 523-1231 
 (b)
if to the Preferred Stockholders, as set forth on Schedule 1; and 
 (c) if to the Principal Stockholders, as set forth on
Schedule 2; 
 All such notices, requests, consents and communications shall be deemed to have been received (i) in the case of personal
delivery, on the date of such delivery, (ii) in the case of mailing, on the third business day following the date of such mailing, (iii) in the case of overnight mail, on the first business day following the date of such mailing, and
(iv) in the case of facsimile transmission, when confirmed by facsimile-machine report. 
 12. Changes. The terms and provisions
hereof may not be modified, amended or terminated, nor any of such provisions waived, temporarily or permanently, except pursuant to a writing executed by a duly authorized representative of the Corporation and the written consent of the Preferred
Stockholders holding at least two-thirds in voting power of the then-outstanding Preferred Stock, calculated in accordance with Section A.6(a) of Article III of the Certificate (including in such calculation any outstanding Restricted Shares held by
such holders); provided, however, that no Preferred Stockholder shall, without its consent, be adversely affected by any such modification, amendment or waiver in any manner in which all other Preferred Stockholders are not likewise
adversely affected; and provided, further, that any provision that requires the vote of the Requisite New Investors may not be modified, amended, terminated or waived without the affirmative vote of the Requisite New Investors. 

13. Spousal Consents. On or before the date hereof, each Principal Stockholder shall deliver to the Corporation the Consent of Spouse
executed and delivered by the spouse of such Principal Stockholder (if married), in substantially the form attached hereto as Exhibit C. 

14. Counterparts. This Agreement may be executed in any number of counterparts, and each such counterpart shall be deemed to be an
original instrument, but all such counterparts together shall constitute but one agreement. 
 15. Headings. The headings of the
various sections hereof have been inserted for convenience of reference only and shall not be deemed to be a part hereof. 

  
 36 

 16. Nouns and Pronouns. Whenever the context may require, any pronouns used herein shall
include the corresponding masculine, feminine or neuter forms, and the singular form of names and pronouns shall include the plural and vice-versa. 

17. Severability. Any provision hereof that is prohibited or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable
such provision in any other jurisdiction. 
 18. Governing Law. This Agreement shall be governed by and construed in accordance with
the laws of the State of Delaware, excluding choice of law rules thereof. 
 [Remainder of page intentionally left blank; signature pages
follow] 

  
 37 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	PROTEOSTASIS THERAPEUTICS, INC.
		
	By:	 	 /s/ Meenu Chhabra

	Name:	 	Meenu Chhabra
	Title:	 	President and Chief Executive Officer

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

	
	PRINCIPAL STOCKHOLDERS:
	
	 /s/ Jeffrey W. Kelly

	Jeffery W. Kelly
	
	 /s/ Andrew Dillin

	Andrew Dillin
	
	 /s/ Richard Morimoto

	Richard I. Morimoto

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	HEALTHCARE VENTURES VIII, L.P.
		
	By:	 	HealthCare Partners VIII, L.P.
		 	 its General Partner

		
	By:	 	HealthCare Partners VIII, LLC
		 	 its General Partner

		
	By:	 	 /s/ Christopher Mirabelli

		
	Name:	 	
	Title:	 	

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	BEACON BIOVENTURES FUND II LIMITED PARTNERSHIP
		
	By:	 	Beacon Bioventures Advisors Fund II Limited Partnership,
		 	 its sole general partner

		
	By:	 	Impresa Management LLC,
		 	 its sole general partner

		
	By:	 	 /s/ Stephen Knight

	Name:	 	Stephen Knight
	Title:	 	Vice President

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	GENZYME CORPORATION
		
	By:	 	 /s/ Karen M. Linehon

	Name:	 	Karen M. Linehon
	Title:	 	Authorized Signatory

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	BIOGEN MA INC.
		
	By:	 	 /s/ Michael Dambach

	Name:	 	Michael Dambach
	Title:	 	VP & Treasurer

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	ELAN SCIENCE ONE LTD.
		
	By:	 	 /s/ Conor Walshe

	Name:	 	Conor Walshe
	Title:	 	Director

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	NOVARTIS BIOVENTURES LTD.
		
	By:	 	 /s/ H.S. Zivi

	Name:	 	H.S. Zivi
	Title:	 	Chairman
		
	By:	 	 /s/ Laurieann Chaikowsky

	Name:	 	Laurieann Chaikowsky
	Title:	 	Authorised Signatory

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	NEW ENTERPRISE ASSOCIATES 12, LIMITED PARTNERSHIP
		
	By:	 	NEA Partners 12, Limited Partnership,
		 	 its General Partner

		
	By:	 	NEA 12 GP, LLC
		 	 its General Partner

		
	By:	 	 /s/ Louis S. Citron

	Name:	 	Louis S. Citron
	Title:	 	Chief Legal Officer
	
	NEA VENTURES 2008, LIMITED PARTNERSHIP
		
	By:	 	 /s/ Louis S. Citron

	Name:	 	Louis S. Citron
	Title:	 	Vice President

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	ASTELLAS PHARMA INC.
		
	By:	 	 /s/ Shunichiro Matsumoto

	Name:	 	Shunichiro Matsumoto
	Title:	 	Vice President, Innovation Management

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	CORMORANT GLOBAL HEALTHCARE MASTER FUND, LP
		
	By:	 	 /s/ Bihua Chen

	Name:	 	Bihua Chen
	Title:	 	Managing Member of the General Partner

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

			
	INVESTOR:
	
	ROCK SPRINGS CAPITAL MASTER FUND LP
		
	By:	 	Rock Springs GP LLC
		
	Its:	 	General Partner
		
	By:	 	 /s/ Graham McPhail

	Name:	 	Graham McPhail
	Title:	 	Managing Director

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 IN WITNESS WHEREOF the parties hereto have executed this Third Amended and Restated
Stockholders’ Agreement on the date first above written. 
  

	
	INVESTOR:
	
	 /s/ Franklin Berger

	Name:  Franklin M. Berger

  
 Signature Page to
Third Amended and Restated Stockholders’ Agreement 

 Schedule 1 

Investors 
 HealthCare Ventures VIII, L.P.

 44 Nassau Street 
 Princeton, NJ 08542 

Fax: (617) 252-4352 
 Beacon Bioventures Fund II 

c/o Fidelity Biosciences 
 Attn.: Mary Bevelock Pendergast 

One Main Street, 13th Floor 
 Cambridge, MA 02142 

Genzyme Corporation 
 500 Kendall Street 

Cambridge, MA 02142 
 Attn: Managing Director, Genzyme Ventures

 Fax: (617) 768-6431 

          with a copy to: 

Genzyme Corporation 
 500 Kendall Street 

Cambridge, MA 02142 
 Attn: Senior Vice President, General Counsel

 Fax: (617) 768-9736 
 New Enterprise
Associates 12, Limited Partnership, and 
 NEA Ventures 2008, Limited Partnership 

c/o New Enterprise Associates 
 1954 Greenspring Drive, Suite 600

 Timonium, MD 21093 
 Fax: (410) 752-7721 

Novartis BioVentures Ltd. 
 131 Front Street 

Hamilton HM 12 
 Bermuda 

Attn.: Chairman and General Counsel 
 Fax: (441) 296-5083 

           with a copy to: 

Novartis Venture Fund 
 Five Cambridge Center, Suite 603 

Cambridge, MA 02142 
 Attn: Henry Skinner 

Email: henry.skinner@nvfund.com 

  
 S-1 

 Schedule 1 (Continued) 

Elan Science One Ltd. 
 Treasury Building 

Lower Grand Canal Street 
 Dublin 2, Ireland 

FAX: +353 1 709 4700 
 Biogen MA Inc. 

225 Binney Street 
 Cambridge, MA 02142 

Astellas Pharma Inc. 
 5-1 Nihonbashi-Honcho 2-Chome, Chuo-ku

 Tokyo 103-8411, Japan 
 Cormorant Global Healthcare Master
Fund, LP 
 200 Clarendon Street 
 52nd Floor 

Boston, MA 02116 
 Rock Springs Capital 

650 S. Exeter Street 
 Suite 1070 

Baltimore, MD 21202 
 Franklin M. Berger 

257 Park Avenue South 
 15th Floor 

New York, NY 10010 

  
 S-2 

 Schedule 2 

Principal Stockholders 
 Jeffery W. Kelly 

8110 El Paseo Grande #407 
 La Jolla, CA 92037 

Fax: (858) 784-9610 
 Email: jwk@scripps.edu 

Andrew Dillin 
 6895 Elverton Drive 

Oakland, CA 94611 
 Email: dillin@berkeley.edu 

Richard I. Morimoto 
 3217 Otto Lane 

Evanston, IL 60201 
 Fax: (847) 491-4461 

Email: rickmorimoto@gmail.com 

  
 S-3EX-10.6

 Exhibit 10.6 

PROTEOSTASIS THERAPEUTICS, INC. 
  

 
 2016 STOCK
OPTION AND INCENTIVE PLAN 
  

	SECTION 1.	GENERAL PURPOSE OF THE PLAN; DEFINITIONS 

 The name of the plan is the Proteostasis
Therapeutics, Inc. 2016 Stock Option and Incentive Plan (the “Plan”). The purpose of the Plan is to encourage and enable the officers, employees, Non-Employee Directors and Consultants of Proteostasis Therapeutics, Inc. (the
“Company”) and its Subsidiaries upon whose judgment, initiative and efforts the Company largely depends for the successful conduct of its business to acquire a proprietary interest in the Company. It is anticipated that providing
such persons with a direct stake in the Company’s welfare will assure a closer identification of their interests with those of the Company and its stockholders, thereby stimulating their efforts on the Company’s behalf and strengthening
their desire to remain with the Company. 
 The following terms shall be defined as set forth below: 

“Act” means the Securities Act of 1933, as amended, and the rules and regulations thereunder. 

“Administrator” means either the Board or the compensation committee of the Board or a similar committee
performing the functions of the compensation committee and which is comprised of not less than two Non-Employee Directors who are independent. 

“Award” or “Awards,” except where referring to a particular
category of grant under the Plan, shall include Incentive Stock Options, Non-Qualified Stock Options, Stock Appreciation Rights, Restricted Stock Units, Restricted Stock Awards, Unrestricted Stock Awards, Cash-Based Awards, Performance Share Awards
and Dividend Equivalent Rights. 
 “Award Certificate” means a written or electronic document setting
forth the terms and provisions applicable to an Award granted under the Plan. Each Award Certificate is subject to the terms and conditions of the Plan. 

“Board” means the Board of Directors of the Company. 

“Cash-Based Award” means an Award entitling the recipient to receive a cash-denominated payment. 

“Code” means the Internal Revenue Code of 1986, as amended, and any successor Code, and related rules,
regulations and interpretations. 
 “Consultant” means any natural person that provides bona fide
services to the Company, and such services are not in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s securities. 

 “Covered Employee” means an employee who is a “Covered
Employee” within the meaning of Section 162(m) of the Code. 
 “Dividend Equivalent Right”
means an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the shares of Stock specified in the Dividend Equivalent Right (or other award to which it relates) if such shares had been issued to and
held by the grantee. 
 “Effective Date” means the date on which the Plan becomes effective as set
forth in Section 21. 
 “Exchange Act” means the Securities Exchange Act of 1934, as amended, and
the rules and regulations thereunder. 
 “Fair Market Value” of the Stock on any given date means the
fair market value of the Stock determined in good faith by the Administrator; provided, however, that if the Stock is admitted to quotation on the National Association of Securities Dealers Automated Quotation System (“NASDAQ”),
NASDAQ Global Market or another national securities exchange, the determination shall be made by reference to market quotations. If there are no market quotations for such date, the determination shall be made by reference to the last date preceding
such date for which there are market quotations; provided further, however, that if the date for which Fair Market Value is determined is the first day when trading prices for the Stock are reported on a national securities exchange, the Fair Market
Value shall be the “Price to the Public” (or equivalent) set forth on the cover page for the final prospectus relating to the Company’s Initial Public Offering. 

“Incentive Stock Option” means any Stock Option designated and qualified as an “incentive stock
option” as defined in Section 422 of the Code. 
 “Initial Public Offering” means first
underwritten, firm commitment public offering pursuant to an effective registration statement under the Act covering the offer and sale by the Company of its equity securities, or such other event as a result of or following which the Stock shall be
publicly held. 
 “Non-Employee Director” means a member of the Board who is not also an employee of
the Company or any Subsidiary. 
 “Non-Qualified Stock Option” means any Stock Option that is not an
Incentive Stock Option. 
 “Option” or “Stock Option” means any
option to purchase shares of Stock granted pursuant to Section 5. 
 “Performance-Based Award”
means any Restricted Stock Award, Restricted Stock Units, Performance Share Award or Cash-Based Award granted to a Covered Employee that is intended to qualify as “performance-based compensation” under Section 162(m) of the Code and
the regulations promulgated thereunder. 

  
 2 

 “Performance Criteria” means the criteria that the
Administrator selects for purposes of establishing the Performance Goal or Performance Goals for an individual for a Performance Cycle. The Performance Criteria (which shall be applicable to the organizational level specified by the Administrator,
including, but not limited to, the Company or a unit, division, group, or Subsidiary of the Company) that will be used to establish Performance Goals are limited to the following: total shareholder return, earnings before interest, taxes,
depreciation and amortization, net income (loss) (either before or after interest, taxes, depreciation and/or amortization), changes in the market price of the Stock, economic value-added, funds from operations or similar measure, sales or revenue,
developmental, clinical or regulatory milestones, acquisitions or strategic transactions, operating income (loss), cash flow (including, but not limited to, operating cash flow and free cash flow), return on capital, assets, equity, or investment,
return on sales, gross or net profit levels, productivity, expense, margins, operating efficiency, customer satisfaction, working capital, earnings (loss) per share of Stock, sales or market shares and number of customers, any of which may be
measured either in absolute terms or as compared to any incremental increase or as compared to results of a peer group. The Committee may appropriately adjust any evaluation performance under a Performance Criterion to exclude any of the following
events that occurs during a Performance Cycle: (i) asset write-downs or impairments, (ii) litigation or claim judgments or settlements, (iii) the effect of changes in tax law, accounting principles or other such laws or provisions
affecting reporting results, (iv) accruals for reorganizations and restructuring programs. (v) any extraordinary non-recurring items, including those described in the Financial Accounting Standards Board’s authoritative guidance
and/or in management’s discussion and analysis of financial condition of operations appearing the Company’s annual report to stockholders for the applicable year, and (vi) any other extraordinary items adjusted from the Company U.S.
GAAP results. 
 “Performance Cycle” means one or more periods of time, which may be of varying and
overlapping durations, as the Administrator may select, over which the attainment of one or more Performance Criteria will be measured for the purpose of determining a grantee’s right to and the payment of a Restricted Stock Award, Restricted
Stock Units, Performance Share Award or Cash-Based Award, the vesting and/or payment of which is subject to the attainment of one or more Performance Goals. Each such period shall not be less than 12 months. 

“Performance Goals” means, for a Performance Cycle, the specific goals established in writing by the
Administrator for a Performance Cycle based upon the Performance Criteria. 
 “Performance Share
Award” means an Award entitling the recipient to acquire shares of Stock upon the attainment of specified Performance Goals. 

“Restricted Shares” means the shares of Stock underlying a Restricted Stock Award that remain subject to a risk of
forfeiture or the Company’s right of repurchase. 
 “Restricted Stock Award” means an Award of
Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant. 

“Restricted Stock Units” means an Award of stock units subject to such restrictions and conditions as
the Administrator may determine at the time of grant. 

  
 3 

 “Sale Event” means (i) the sale of all or
substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity, (ii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding voting power and outstanding
stock immediately prior to such transaction do not own a majority of the outstanding voting power and outstanding stock or other equity interests of the resulting or successor entity (or its ultimate parent, if applicable) immediately upon
completion of such transaction, (iii) the sale of all of the Stock of the Company to an unrelated person, entity or group thereof acting in concert, or (iv) any other transaction in which the owners of the Company’s outstanding voting
power immediately prior to such transaction do not own at least a majority of the outstanding voting power of the Company or any successor entity immediately upon completion of the transaction other than as a result of the acquisition of securities
directly from the Company. 
 “Sale Price” means the value as determined by the Administrator of the consideration
payable, or otherwise to be received by stockholders, per share of Stock pursuant to a Sale Event. 
 “Section
409A” means Section 409A of the Code and the regulations and other guidance promulgated thereunder. 

“Stock” means the Common Stock, par value $0.001 per share, of the Company, subject to adjustments
pursuant to Section 3. 
 “Stock Appreciation Right” means an Award entitling the recipient to
receive shares of Stock having a value equal to the excess of the Fair Market Value of the Stock on the date of exercise over the exercise price of the Stock Appreciation Right multiplied by the number of shares of Stock with respect to which the
Stock Appreciation Right shall have been exercised. 
 “Subsidiary” means any corporation or other
entity (other than the Company) in which the Company has at least a 50 percent interest, either directly or indirectly. 

“Ten Percent Owner” means an employee who owns or is deemed to own (by reason of the attribution rules
of Section 424(d) of the Code) more than 10 percent of the combined voting power of all classes of stock of the Company or any parent or subsidiary corporation. 

“Unrestricted Stock Award” means an Award of shares of Stock free of any restrictions. 

 

	SECTION 2.	ADMINISTRATION OF PLAN; ADMINISTRATOR AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS 

(a) Administration of Plan. The Plan shall be administered by the Administrator. 

(b) Powers of Administrator. The Administrator shall have the power and authority to grant Awards consistent with the terms of the
Plan, including the power and authority: 
 (i) to select the individuals to whom Awards may from time to time be granted; 

(ii) to determine the time or times of grant, and the extent, if any, of Incentive Stock Options, Non-Qualified Stock Options, Stock
Appreciation Rights, Restricted Stock 

  
 4 

 
Awards, Restricted Stock Units, Unrestricted Stock Awards, Cash-Based Awards, Performance Share Awards and Dividend Equivalent Rights, or any combination of the foregoing, granted to any one or
more grantees; 
 (iii) to determine the number of shares of Stock to be covered by any Award; 

(iv) to determine and modify from time to time the terms and conditions, including restrictions, not inconsistent with the terms of the Plan,
of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the forms of Award Certificates; 

(v) to accelerate at any time the exercisability or vesting of all or any portion of any Award in circumstances involving the grantee’s
death, disability, retirement, termination of employment, or a change in control (including a Sale Event); 
 (vi) subject to the provisions
of Section 5(c), to extend at any time the period in which Stock Options may be exercised; and 
 (vii) at any time to adopt, alter and
repeal such rules, guidelines and practices for administration of the Plan and for its own acts and proceedings as it shall deem advisable; to interpret the terms and provisions of the Plan and any Award (including related written instruments); to
make all determinations it deems advisable for the administration of the Plan; to decide all disputes arising in connection with the Plan; and to otherwise supervise the administration of the Plan. 

All decisions and interpretations of the Administrator shall be binding on all persons, including the Company and Plan grantees. 

(c) Delegation of Authority to Grant Awards. Subject to applicable law, the Administrator, in its discretion, may delegate to the Chief
Executive Officer of the Company all or part of the Administrator’s authority and duties with respect to the granting of Awards to individuals who are (i) not subject to the reporting and other provisions of Section 16 of the Exchange
Act and (ii) not Covered Employees. Any such delegation by the Administrator shall include a limitation as to the amount of Stock underlying Awards that may be granted during the period of the delegation and shall contain guidelines as to the
determination of the exercise price and the vesting criteria. The Administrator may revoke or amend the terms of a delegation at any time but such action shall not invalidate any prior actions of the Administrator’s delegate or delegates that
were consistent with the terms of the Plan. 
 (d) Award Certificate. Awards under the Plan shall be evidenced by Award Certificates
that set forth the terms, conditions and limitations for each Award which may include, without limitation, the term of an Award and the provisions applicable in the event employment or service terminates. 

(e) Indemnification. Neither the Board nor the Administrator, nor any member of either or any delegate thereof, shall be liable for any
act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Administrator (and any delegate thereof) shall be entitled in all cases to indemnification and

  
 5 

 
reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent
permitted by law and/or under the Company’s articles or bylaws or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual and the
Company. 
 (f) Foreign Award Recipients. Notwithstanding any provision of the Plan to the contrary, in order to comply with the laws
in other countries in which the Company and its Subsidiaries operate or have employees or other individuals eligible for Awards, the Administrator, in its sole discretion, shall have the power and authority to: (i) determine which Subsidiaries
shall be covered by the Plan; (ii) determine which individuals outside the United States are eligible to participate in the Plan; (iii) modify the terms and conditions of any Award granted to individuals outside the United States to comply
with applicable foreign laws; (iv) establish subplans and modify exercise procedures and other terms and procedures, to the extent the Administrator determines such actions to be necessary or advisable (and such subplans and/or modifications
shall be attached to this Plan as appendices); provided, however, that no such subplans and/or modifications shall increase the share limitations contained in Section 3(a) hereof; and (v) take any action, before or after an Award is made,
that the Administrator determines to be necessary or advisable to obtain approval or comply with any local governmental regulatory exemptions or approvals. Notwithstanding the foregoing, the Administrator may not take any actions hereunder, and no
Awards shall be granted, that would violate the Exchange Act or any other applicable United States securities law, the Code, or any other applicable United States governing statute or law. 

 

	SECTION 3.	STOCK ISSUABLE UNDER THE PLAN; MERGERS; SUBSTITUTION 

 (a) Stock Issuable. The
maximum number of shares of Stock reserved and available for issuance under the Plan shall be 1,581,839 shares (the “Initial Limit”), subject to adjustment as provided in Section 3(c), plus on January 1, 2017 and each
January 1 thereafter, the number of shares of Stock reserved and available for issuance under the Plan shall be cumulatively increased by three percent (3%) of the number of shares of Stock issued and outstanding on the immediately
preceding December 31 or such lesser number of shares of Stock as determined by the Administrator (the “Annual Increase”). Subject to such overall limitation, the maximum aggregate number of shares of Stock that may be issued
in the form of Incentive Stock Options shall not exceed the Initial Limit cumulatively increased on January 1, 2017 and on each January 1 thereafter by the lesser of the Annual Increase for such year or 740,041 shares of Stock, subject in
all cases to adjustment as provided in Section 3(c). The shares of Stock underlying any Awards under the Plan and under the Company’s 2008 Equity Incentive Plan that are forfeited, canceled, held back upon exercise of an Option or
settlement of an Award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of Stock or otherwise terminated (other than by exercise) shall be added back to the shares of Stock
available for issuance under the Plan. In the event the Company repurchases shares of Stock on the open market, such shares shall not be added to the shares of Stock available for issuance under the Plan. Subject to such overall limitations, shares
of Stock may be issued up to such maximum number pursuant to any type or types of Award; provided, however, that Stock Options or Stock Appreciation Rights with respect to no more than 740,041 shares of Stock may be granted to any one individual
grantee during any one calendar year period. The shares available for issuance under the Plan may be authorized but unissued shares of Stock or shares of Stock reacquired by the Company. 

  
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 (b) Maximum Awards to Non-Employee Directors. Notwithstanding anything to the contrary in
this Plan, the value of all Awards awarded under this Plan and all other cash compensation paid by the Company to any Non-Employee Director in any calendar year shall not exceed $500,000. For the purpose of this limitation, the value of any Award
shall be its grant date fair value, as determined in accordance with ASC 718 or successor provision but excluding the impact of estimated forfeitures related to service-based vesting provisions. 

(c) Changes in Stock. Subject to Section 3(d) hereof, if, as a result of any reorganization, recapitalization, reclassification,
stock dividend, stock split, reverse stock split or other similar change in the Company’s capital stock, the outstanding shares of Stock are increased or decreased or are exchanged for a different number or kind of shares or other securities of
the Company, or additional shares or new or different shares or other securities of the Company or other non-cash assets are distributed with respect to such shares of Stock or other securities, or, if, as a result of any merger or consolidation,
sale of all or substantially all of the assets of the Company, the outstanding shares of Stock are converted into or exchanged for securities of the Company or any successor entity (or a parent or subsidiary thereof), the Administrator shall make an
appropriate or proportionate adjustment in (i) the maximum number of shares reserved for issuance under the Plan, including the maximum number of shares that may be issued in the form of Incentive Stock Options, (ii) the number of Stock
Options or Stock Appreciation Rights that can be granted to any one individual grantee and the maximum number of shares that may be granted under a Performance-Based Award, (iii) the number and kind of shares or other securities subject to any
then outstanding Awards under the Plan, (iv) the repurchase price, if any, per share subject to each outstanding Restricted Stock Award, and (v) the exercise price for each share subject to any then outstanding Stock Options and Stock
Appreciation Rights under the Plan, without changing the aggregate exercise price (i.e., the exercise price multiplied by the number of Stock Options and Stock Appreciation Rights) as to which such Stock Options and Stock Appreciation Rights remain
exercisable. The Administrator shall also make equitable or proportionate adjustments in the number of shares subject to outstanding Awards and the exercise price and the terms of outstanding Awards to take into consideration cash dividends paid
other than in the ordinary course or any other extraordinary corporate event. The adjustment by the Administrator shall be final, binding and conclusive. No fractional shares of Stock shall be issued under the Plan resulting from any such
adjustment, but the Administrator in its discretion may make a cash payment in lieu of fractional shares. 
 (d) Mergers and Other
Transactions. In the case of and subject to the consummation of a Sale Event, the parties thereto may cause the assumption or continuation of Awards theretofore granted by the successor entity, or the substitution of such Awards with new Awards
of the successor entity or parent thereof, with appropriate adjustment as to the number and kind of shares and, if appropriate, the per share exercise prices, as such parties shall agree. To the extent the parties to such Sale Event do not provide
for the assumption, continuation or substitution of Awards, upon the effective time of the Sale Event, the Plan and all outstanding Awards granted hereunder shall terminate. In such case except as may be otherwise provided in the relevant Award
Certificate, all Awards with time-based vesting, conditions or restrictions shall become fully vested and nonforfeitable as of the effective time of the Sale Event and all 

  
 7 

 
Awards with conditions and restrictions relating to the attainment of performance goals may become vested and nonforfeitable in connection with a Sale Event in the Administrator’s discretion
or to the extent specified in the relevant Award Certificate. In the event of such termination, (i) the Company shall have the option (in its sole discretion) to make or provide for a payment, in cash or in kind, to the grantees holding Options
and Stock Appreciation Rights, in exchange for the cancellation thereof, in an amount equal to the difference between (A) the Sale Price multiplied by the number of shares of Stock subject to outstanding Options and Stock Appreciation Rights
(to the extent then exercisable at prices not in excess of the Sale Price) and (B) the aggregate exercise price of all such outstanding Options and Stock Appreciation Rights; or (ii) each grantee shall be permitted, within a specified
period of time prior to the consummation of the Sale Event as determined by the Administrator, to exercise all outstanding Options and Stock Appreciation Rights (to the extent then exercisable) held by such grantee. The Company shall also have the
option (in its sole discretion) to make or provide for a payment, in cash or in kind, to the grantees holding other Awards in an amount equal to the Sale Price multiplied by the number of vested shares of Stock underlying such Awards. 

 

	SECTION 4.	ELIGIBILITY 

 Grantees under the Plan will be such full or part-time officers and other
employees, Non-Employee Directors and Consultants of the Company and its Subsidiaries as are selected from time to time by the Administrator in its sole discretion. 
  

	SECTION 5.	STOCK OPTIONS 

 (a) Award of Stock Options. The Administrator may grant Stock
Options under the Plan. Any Stock Option granted under the Plan shall be in such form as the Administrator may from time to time approve. 

Stock Options granted under the Plan may be either Incentive Stock Options or Non-Qualified Stock Options. Incentive Stock Options may be
granted only to employees of the Company or any Subsidiary that is a “subsidiary corporation” within the meaning of Section 424(f) of the Code. To the extent that any Option does not qualify as an Incentive Stock Option, it shall be
deemed a Non-Qualified Stock Option. 
 Stock Options granted pursuant to this Section 5 shall be subject to the following terms and
conditions and shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Administrator shall deem desirable. If the Administrator so determines, Stock Options may be granted in lieu of cash compensation
at the optionee’s election, subject to such terms and conditions as the Administrator may establish. 
 (b) Exercise Price. The
exercise price per share for the Stock covered by a Stock Option granted pursuant to this Section 5 shall be determined by the Administrator at the time of grant but shall not be less than 100 percent of the Fair Market Value on the date of
grant. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the option price of such Incentive Stock Option shall be not less than 110 percent of the Fair Market Value on the grant date. 

  
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 (c) Option Term. The term of each Stock Option shall be fixed by the Administrator, but no
Stock Option shall be exercisable more than ten years after the date the Stock Option is granted. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the term of such Stock Option shall be no more than five years from
the date of grant. 
 (d) Exercisability; Rights of a Stockholder. Stock Options shall become exercisable at such time or times,
whether or not in installments, as shall be determined by the Administrator at or after the grant date. The Administrator may at any time accelerate the exercisability of all or any portion of any Stock Option. An optionee shall have the rights of a
stockholder only as to shares acquired upon the exercise of a Stock Option and not as to unexercised Stock Options. 
 (e) Method of
Exercise. Stock Options may be exercised in whole or in part, by giving written or electronic notice of exercise to the Company, specifying the number of shares to be purchased. Payment of the purchase price may be made by one or more of the
following methods except to the extent otherwise provided in the Option Award Certificate: 
 (i) In cash, by certified or bank check or
other instrument acceptable to the Administrator; 
 (ii) Through the delivery (or attestation to the ownership following such procedures as
the Company may prescribe) of shares of Stock that are not then subject to restrictions under any Company plan. Such surrendered shares shall be valued at Fair Market Value on the exercise date; 

(iii) By the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to
promptly deliver to the Company cash or a check payable and acceptable to the Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with
such procedures and enter into such agreements of indemnity and other agreements as the Company shall prescribe as a condition of such payment procedure; or 

(iv) With respect to Stock Options that are not Incentive Stock Options, by a “net exercise” arrangement pursuant to which the
Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the aggregate exercise price. 

Payment instruments will be received subject to collection. The transfer to the optionee on the records of the Company or of the transfer agent of the shares
of Stock to be purchased pursuant to the exercise of a Stock Option will be contingent upon receipt from the optionee (or a purchaser acting in his stead in accordance with the provisions of the Stock Option) by the Company of the full purchase
price for such shares and the fulfillment of any other requirements contained in the Option Award Certificate or applicable provisions of laws (including the satisfaction of any withholding taxes that the Company is obligated to withhold with
respect to the optionee). In the event an optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock transferred to the optionee upon the exercise of the Stock Option
shall be net of the number of attested shares. In the event that the Company establishes, for itself or using the services of a third party, an 

  
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automated system for the exercise of Stock Options, such as a system using an internet website or interactive voice response, then the paperless exercise of Stock Options may be permitted through
the use of such an automated system. 
 (f) Annual Limit on Incentive Stock Options. To the extent required for “incentive stock
option” treatment under Section 422 of the Code, the aggregate Fair Market Value (determined as of the time of grant) of the shares of Stock with respect to which Incentive Stock Options granted under this Plan and any other plan of the
Company or its parent and subsidiary corporations become exercisable for the first time by an optionee during any calendar year shall not exceed $100,000. To the extent that any Stock Option exceeds this limit, it shall constitute a Non-Qualified
Stock Option. 
  

	SECTION 6.	STOCK APPRECIATION RIGHTS 

 (a) Award of Stock Appreciation Rights. The
Administrator may grant Stock Appreciation Rights under the Plan. A Stock Appreciation Right is an Award entitling the recipient to receive shares of Stock having a value equal to the excess of the Fair Market Value of a share of Stock on the date
of exercise over the exercise price of the Stock Appreciation Right multiplied by the number of shares of Stock with respect to which the Stock Appreciation Right shall have been exercised. 

(b) Exercise Price of Stock Appreciation Rights. The exercise price of a Stock Appreciation Right shall not be less than 100 percent of
the Fair Market Value of the Stock on the date of grant. 
 (c) Grant and Exercise of Stock Appreciation Rights. Stock Appreciation
Rights may be granted by the Administrator independently of any Stock Option granted pursuant to Section 5 of the Plan. 
 (d) Terms
and Conditions of Stock Appreciation Rights. Stock Appreciation Rights shall be subject to such terms and conditions as shall be determined by the Administrator at the time of grant. The term of a Stock Appreciation Right may not exceed ten
years. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among individual Awards and grantees. 
  

	SECTION 7.	RESTRICTED STOCK AWARDS 

 (a) Nature of Restricted Stock Awards. The Administrator
may grant Restricted Stock Awards under the Plan. A Restricted Stock Award is any Award of Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant. Conditions may be based on continuing
employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among
individual Awards and grantees. 
 (b) Rights as a Stockholder. Upon the grant of the Restricted Stock Award and payment of any
applicable purchase price, a grantee shall have the rights of a stockholder with respect to the voting of the Restricted Shares and receipt of dividends; provided that if the lapse 

  
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of restrictions with respect to the Restricted Stock Award is tied to the attainment of performance goals, any dividends paid by the Company during the performance period shall accrue and shall
not be paid to the grantee until and to the extent the performance goals are met with respect to the Restricted Stock Award. Unless the Administrator shall otherwise determine, (i) uncertificated Restricted Shares shall be accompanied by a
notation on the records of the Company or the transfer agent to the effect that they are subject to forfeiture until such Restricted Shares are vested as provided in Section 7(d) below, and (ii) certificated Restricted Shares shall remain
in the possession of the Company until such Restricted Shares are vested as provided in Section 7(d) below, and the grantee shall be required, as a condition of the grant, to deliver to the Company such instruments of transfer as the
Administrator may prescribe. 
 (c) Restrictions. Restricted Shares may not be sold, assigned, transferred, pledged or otherwise
encumbered or disposed of except as specifically provided herein or in the Restricted Stock Award Certificate. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 18 below, in writing
after the Award is issued, if a grantee’s employment (or other service relationship) with the Company and its Subsidiaries terminates for any reason, any Restricted Shares that have not vested at the time of termination shall automatically and
without any requirement of notice to such grantee from or other action by or on behalf of, the Company be deemed to have been reacquired by the Company at its original purchase price (if any) from such grantee or such grantee’s legal
representative simultaneously with such termination of employment (or other service relationship), and thereafter shall cease to represent any ownership of the Company by the grantee or rights of the grantee as a stockholder. Following such deemed
reacquisition of Restricted Shares that are represented by physical certificates, a grantee shall surrender such certificates to the Company upon request without consideration. 

(d) Vesting of Restricted Shares. The Administrator at the time of grant shall specify the date or dates and/or the attainment of
pre-established performance goals, objectives and other conditions on which the non-transferability of the Restricted Shares and the Company’s right of repurchase or forfeiture shall lapse. Subsequent to such date or dates and/or the attainment
of such pre-established performance goals, objectives and other conditions, the shares on which all restrictions have lapsed shall no longer be Restricted Shares and shall be deemed “vested.” 

 

	SECTION 8.	RESTRICTED STOCK UNITS 

 (a) Nature of Restricted Stock Units. The Administrator
may grant Restricted Stock Units under the Plan. A Restricted Stock Unit is an Award of stock units that may be settled in shares of Stock upon the satisfaction of such restrictions and conditions at the time of grant. Conditions may be based on
continuing employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may
differ among individual Awards and grantees. Except in the case of Restricted Stock Units with a deferred settlement date that complies with Section 409A, at the end of the vesting period, the Restricted Stock Units, to the extent vested, shall
be settled in the form of shares of Stock. Restricted Stock Units with deferred settlement dates are subject to Section 409A, and shall contain such additional terms and conditions as the Administrator shall determine in its sole discretion in
order to comply with the requirements of Section 409A. 

  
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 (b) Election to Receive Restricted Stock Units in Lieu of Compensation. The Administrator
may, in its sole discretion, permit a grantee to elect to receive a portion of future cash compensation otherwise due to such grantee in the form of an award of Restricted Stock Units. Any such election shall be made in writing and shall be
delivered to the Company no later than the date specified by the Administrator and in accordance with Section 409A and such other rules and procedures established by the Administrator. Any such future cash compensation that the grantee elects
to defer shall be converted to a fixed number of Restricted Stock Units based on the Fair Market Value of Stock on the date the compensation would otherwise have been paid to the grantee if such payment had not been deferred as provided herein. The
Administrator shall have the sole right to determine whether and under what circumstances to permit such elections and to impose such limitations and other terms and conditions thereon as the Administrator deems appropriate. Any Restricted Stock
Units that are elected to be received in lieu of cash compensation shall be fully vested, unless otherwise provided in the Award Certificate. 

(c) Rights as a Stockholder. A grantee shall have the rights as a stockholder only as to shares of Stock acquired by the grantee upon
settlement of Restricted Stock Units; provided, however, that the grantee may be credited with Dividend Equivalent Rights with respect to the stock units underlying his Restricted Stock Units, subject to the provisions of Section 11 and such
terms and conditions as the Administrator may determine. 
 (d) Termination. Except as may otherwise be provided by the Administrator
either in the Award Certificate or, subject to Section 18 below, in writing after the Award is issued, a grantee’s right in all Restricted Stock Units that have not vested shall automatically terminate upon the grantee’s termination
of employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason. 
  

	SECTION 9.	UNRESTRICTED STOCK AWARDS 

 Grant or Sale of Unrestricted Stock. The Administrator
may grant (or sell at par value or such higher purchase price determined by the Administrator) an Unrestricted Stock Award under the Plan. An Unrestricted Stock Award is an Award pursuant to which the grantee may receive shares of Stock free of any
restrictions under the Plan. Unrestricted Stock Awards may be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to such grantee. 

 

	SECTION 10.	CASH-BASED AWARDS 

 Grant of Cash-Based Awards. The Administrator may grant
Cash-Based Awards under the Plan. A Cash-Based Award is an award that entitles the grantee to a payment in cash upon the attainment of specified Performance Goals. The Administrator shall determine the maximum duration of the Cash-Based Award, the
amount of cash to which the Cash-Based Award pertains, the conditions upon which the Cash-Based Award shall become vested or payable, and such other provisions as the Administrator shall determine. Each Cash-Based Award shall specify a
cash-denominated payment amount, formula or payment ranges as determined by the Administrator. Payment, if any, with respect to a Cash-Based Award shall be made in accordance with the terms of the Award and may be made in cash. 

  
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	SECTION 11.	PERFORMANCE SHARE AWARDS 

 (a) Nature of Performance Share Awards. The
Administrator may grant Performance Share Awards under the Plan. A Performance Share Award is an Award entitling the grantee to receive shares of Stock upon the attainment of performance goals. The Administrator shall determine whether and to whom
Performance Share Awards shall be granted, the Performance Goals, the periods during which performance is to be measured, which may not be less than one year except in the case of a Sale Event, and such other limitations and conditions as the
Administrator shall determine. 
 (b) Rights as a Stockholder. A grantee receiving a Performance Share Award shall have the rights of
a stockholder only as to shares of Stock actually received by the grantee under the Plan and not with respect to shares subject to the Award but not actually received by the grantee. A grantee shall be entitled to receive shares of Stock under a
Performance Share Award only upon satisfaction of all conditions specified in the Performance Share Award Certificate (or in a performance plan adopted by the Administrator). 

(c) Termination. Except as may otherwise be provided by the Administrator either in the Award agreement or, subject to Section 18
below, in writing after the Award is issued, a grantee’s rights in all Performance Share Awards shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its
Subsidiaries for any reason. 
  

	SECTION 12.	PERFORMANCE-BASED AWARDS TO COVERED EMPLOYEES 

 (a) Performance-Based Awards. The
Administrator may grant one or more Performance-Based Awards in the form of a Restricted Stock Award, Restricted Stock Units, Performance Share Awards or Cash-Based Award payable upon the attainment of Performance Goals that are established by the
Administrator and relate to one or more of the Performance Criteria, in each case on a specified date or dates or over any period or periods determined by the Administrator. The Administrator shall define in an objective fashion the manner of
calculating the Performance Criteria it selects to use for any Performance Cycle. Depending on the Performance Criteria used to establish such Performance Goals, the Performance Goals may be expressed in terms of overall Company performance or the
performance of a division, business unit, or an individual. Each Performance-Based Award shall comply with the provisions set forth below. 

(b) Grant of Performance-Based Awards. With respect to each Performance-Based Award granted to a Covered Employee, the Administrator
shall select, within the first 90 days of a Performance Cycle (or, if shorter, within the maximum period allowed under Section 162(m) of the Code) the Performance Criteria for such grant, and the Performance Goals with respect to each
Performance Criterion (including a threshold level of performance below which no amount will become payable with respect to such Award). Each Performance-Based Award will specify the amount payable, or the formula for determining the amount payable,
upon achievement of the various applicable performance targets. The Performance Criteria established by the Administrator may be (but need not be) different for each Performance Cycle and different Performance Goals may be applicable to
Performance-Based Awards to different Covered Employees. 

  
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 (c) Payment of Performance-Based Awards. Following the completion of a Performance Cycle,
the Administrator shall meet to review and certify in writing whether, and to what extent, the Performance Goals for the Performance Cycle have been achieved and, if so, to also calculate and certify in writing the amount of the Performance-Based
Awards earned for the Performance Cycle. The Administrator shall then determine the actual size of each Covered Employee’s Performance-Based Award, and, in doing so, may reduce or eliminate the amount of the Performance-Based Award for a
Covered Employee if, in its sole judgment, such reduction or elimination is appropriate. 
 (d) Maximum Award Payable. The maximum
Performance-Based Award payable to any one Covered Employee under the Plan for a Performance Cycle is 462,526 shares of Stock (subject to adjustment as provided in Section 3(c) hereof) or $2,000,000 in the case of a Performance-Based Award that
is a Cash-Based Award. 
  

	SECTION 13.	DIVIDEND EQUIVALENT RIGHTS 

 (a) Dividend Equivalent Rights. The Administrator may
grant Dividend Equivalent Rights under the Plan. A Dividend Equivalent Right is an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the shares of Stock specified in the Dividend Equivalent Right (or
other Award to which it relates) if such shares had been issued to the grantee. A Dividend Equivalent Right may be granted hereunder to any grantee as a component of an award of Restricted Stock Units or Performance Share Award or as a freestanding
award. The terms and conditions of Dividend Equivalent Rights shall be specified in the Award Certificate. Dividend equivalents credited to the holder of a Dividend Equivalent Right may be paid currently or may be deemed to be reinvested in
additional shares of Stock, which may thereafter accrue additional equivalents. Any such reinvestment shall be at Fair Market Value on the date of reinvestment or such other price as may then apply under a dividend reinvestment plan sponsored by the
Company, if any. Dividend Equivalent Rights may be settled in cash or shares of Stock or a combination thereof, in a single installment or installments. A Dividend Equivalent Right granted as a component of an Award of Restricted Stock Units or
Performance Share Award shall provide that such Dividend Equivalent Right shall be settled only upon settlement or payment of, or lapse of restrictions on, such other Award, and that such Dividend Equivalent Right shall expire or be forfeited or
annulled under the same conditions as such other Award. 
 (b) Termination. Except as may otherwise be provided by the Administrator
either in the Award Certificate or, subject to Section 18 below, in writing after the Award is issued, a grantee’s rights in all Dividend Equivalent Rights shall automatically terminate upon the grantee’s termination of employment (or
cessation of service relationship) with the Company and its Subsidiaries for any reason. 

  
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	SECTION 14.	TRANSFERABILITY OF AWARDS 

 (a) Transferability. Except as provided in
Section 14(b) below, during a grantee’s lifetime, his or her Awards shall be exercisable only by the grantee, or by the grantee’s legal representative or guardian in the event of the grantee’s incapacity. No Awards shall be sold,
assigned, transferred or otherwise encumbered or disposed of by a grantee other than by will or by the laws of descent and distribution or pursuant to a domestic relations order. No Awards shall be subject, in whole or in part, to attachment,
execution, or levy of any kind, and any purported transfer in violation hereof shall be null and void. 
 (b) Administrator Action.
Notwithstanding Section 14(a), the Administrator, in its discretion, may provide either in the Award Certificate regarding a given Award or by subsequent written approval that the grantee may transfer his or her Non-Qualified Stock Options to
his or her immediate family members, to trusts for the benefit of such family members, or to partnerships in which such family members are the only partners, provided that the transferee agrees in writing with the Company to be bound by all of the
terms and conditions of this Plan and the applicable Award. In no event may an Award be transferred by a grantee for value. 
 (c) Family
Member. For purposes of Section 14(b), “family member” shall mean a grantee’s child, stepchild, grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law,
son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, any person sharing the grantee’s household (other than a tenant of the grantee), a trust in which these persons (or the grantee) have more than 50
percent of the beneficial interest, a foundation in which these persons (or the grantee) control the management of assets, and any other entity in which these persons (or the grantee) own more than 50 percent of the voting interests. 

(d) Designation of Beneficiary. To the extent permitted by the Company, each grantee to whom an Award has been made under the Plan may
designate a beneficiary or beneficiaries to exercise any Award or receive any payment under any Award payable on or after the grantee’s death. Any such designation shall be on a form provided for that purpose by the Administrator and shall not
be effective until received by the Administrator. If no beneficiary has been designated by a deceased grantee, or if the designated beneficiaries have predeceased the grantee, the beneficiary shall be the grantee’s estate. 

 

	SECTION 15.	TAX WITHHOLDING 

 (a) Payment by Grantee. Each grantee shall, no later than the
date as of which the value of an Award or of any Stock or other amounts received thereunder first becomes includable in the gross income of the grantee for Federal income tax purposes, pay to the Company, or make arrangements satisfactory to the
Administrator regarding payment of, any Federal, state, or local taxes of any kind required by law to be withheld by the Company with respect to such income. The Company and its Subsidiaries shall, to the extent permitted by law, have the right to
deduct any such taxes from any payment of any kind otherwise due to the grantee. The Company’s obligation to deliver evidence of book entry (or stock certificates) to any grantee is subject to and conditioned on tax withholding obligations
being satisfied by the grantee. 

  
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 (b) Payment in Stock. Subject to approval by the Administrator, a grantee may elect to
have the Company’s minimum required tax withholding obligation satisfied, in whole or in part, by authorizing the Company to withhold from shares of Stock to be issued pursuant to any Award a number of shares with an aggregate Fair Market Value
(as of the date the withholding is effected) that would satisfy the withholding amount due. The Administrator may also require Awards to be subject to mandatory share withholding up to the required withholding amount. For purposes of share
withholding, the Fair Market Value of withheld shares shall be determined in the same manner as the value of Stock includible in income of the grantee. 
  

	SECTION 16.	SECTION 409A AWARDS 

 To the extent that any Award is determined to constitute
“nonqualified deferred compensation” within the meaning of Section 409A (a “409A Award”), the Award shall be subject to such additional rules and requirements as specified by the Administrator from time to time in
order to comply with Section 409A. In this regard, if any amount under a 409A Award is payable upon a “separation from service” (within the meaning of Section 409A) to a grantee who is then considered a “specified
employee” (within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of (i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s
death, but only to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or additional tax imposed pursuant to Section 409A. Further, the settlement of any such Award may not be accelerated
except to the extent permitted by Section 409A. 
  

	SECTION 17.	TERMINATION OF EMPLOYMENT, TRANSFER, LEAVE OF ABSENCE, ETC. 

 (a) Termination of
Employment. If the grantee’s employer ceases to be a Subsidiary, the grantee shall be deemed to have terminated employment for purposes of the Plan. 

(b) For purposes of the Plan, the following events shall not be deemed a termination of employment: 

(i) a transfer to the employment of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary to another; or

 (ii) an approved leave of absence for military service or sickness, or for any other purpose approved by the Company, if the
employee’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise so provides in writing. 

 

	SECTION 18.	AMENDMENTS AND TERMINATION 

 The Board may, at any time, amend or discontinue the Plan
and the Administrator may, at any time, amend or cancel any outstanding Award for the purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any

  
 16 

 
outstanding Award without the holder’s consent. Except as provided in Section 3(c) or 3(d), without prior stockholder approval, in no event may the Administrator exercise its discretion
to reduce the exercise price of outstanding Stock Options or Stock Appreciation Rights or effect repricing through cancellation and re-grants or cancellation of Stock Options or Stock Appreciation Rights in exchange for cash or other Awards. To the
extent required under the rules of any securities exchange or market system on which the Stock is listed, to the extent determined by the Administrator to be required by the Code to ensure that Incentive Stock Options granted under the Plan are
qualified under Section 422 of the Code, or to ensure that compensation earned under Awards qualifies as performance-based compensation under Section 162(m) of the Code, Plan amendments shall be subject to approval by the Company
stockholders entitled to vote at a meeting of stockholders. Nothing in this Section 18 shall limit the Administrator’s authority to take any action permitted pursuant to Section 3(c) or 3(d). 

 

	SECTION 19.	STATUS OF PLAN 

 With respect to the portion of any Award that has not been exercised and
any payments in cash, Stock or other consideration not received by a grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Administrator shall otherwise expressly determine in connection with any
Award or Awards. In its sole discretion, the Administrator may authorize the creation of trusts or other arrangements to meet the Company’s obligations to deliver Stock or make payments with respect to Awards hereunder, provided that the
existence of such trusts or other arrangements is consistent with the foregoing sentence. 
  

	SECTION 20.	GENERAL PROVISIONS 

 (a) No Distribution. The Administrator may require each
person acquiring Stock pursuant to an Award to represent to and agree with the Company in writing that such person is acquiring the shares without a view to distribution thereof. 

(b) Delivery of Stock Certificates. Stock certificates to grantees under this Plan shall be deemed delivered for all purposes when the
Company or a stock transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company. Uncertificated Stock shall be deemed
delivered for all purposes when the Company or a Stock transfer agent of the Company shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known
address on file with the Company, notice of issuance and recorded the issuance in its records (which may include electronic “book entry” records). Notwithstanding anything herein to the contrary, the Company shall not be required to issue
or deliver any certificates evidencing shares of Stock pursuant to the exercise of any Award, unless and until the Administrator has determined, with advice of counsel (to the extent the Administrator deems such advice necessary or advisable), that
the issuance and delivery of such certificates is in compliance with all applicable laws, regulations of governmental authorities and, if applicable, the requirements of any exchange on which the shares of Stock are listed, quoted or traded. All
Stock certificates delivered pursuant to the Plan shall be subject to any stop-transfer orders and other restrictions as the Administrator deems necessary or advisable to comply with federal, state or foreign jurisdiction, securities or other laws,
rules and quotation system on which the Stock is listed, quoted or traded. The 

  
 17 

 
Administrator may place legends on any Stock certificate to reference restrictions applicable to the Stock. In addition to the terms and conditions provided herein, the Administrator may require
that an individual make such reasonable covenants, agreements, and representations as the Administrator, in its discretion, deems necessary or advisable in order to comply with any such laws, regulations, or requirements. The Administrator shall
have the right to require any individual to comply with any timing or other restrictions with respect to the settlement or exercise of any Award, including a window-period limitation, as may be imposed in the discretion of the Administrator. 

(c) Stockholder Rights. Until Stock is deemed delivered in accordance with Section 20(b), no right to vote or receive dividends or
any other rights of a stockholder will exist with respect to shares of Stock to be issued in connection with an Award, notwithstanding the exercise of a Stock Option or any other action by the grantee with respect to an Award. 

(d) Other Compensation Arrangements; No Employment Rights. Nothing contained in this Plan shall prevent the Board from adopting other
or additional compensation arrangements, including trusts, and such arrangements may be either generally applicable or applicable only in specific cases. The adoption of this Plan and the grant of Awards do not confer upon any employee any right to
continued employment with the Company or any Subsidiary. 
 (e) Trading Policy Restrictions. Option exercises and other Awards under
the Plan shall be subject to the Company’s insider trading policies and procedures, as in effect from time to time. 
 (f) Clawback
Policy. Awards under the Plan shall be subject to the Company’s clawback policy, as may be adopted and as in effect from time to time. 
  

	SECTION 21.	EFFECTIVE DATE OF PLAN 

 This Plan shall become effective on the day immediately
preceding the date of the effectiveness of the Company’s registration statement on Form S-1 filed in connection with the Initial Public Offering following stockholder approval of the Plan in accordance with applicable state law, the
Company’s bylaws and articles of incorporation, and applicable stock exchange rules or pursuant to written consent. No grants of Stock Options and other Awards may be made hereunder after the tenth anniversary of the Effective Date and no
grants of Incentive Stock Options may be made hereunder after the tenth anniversary of the date the Plan is approved by the Board. 

  
 18 

	SECTION 22.	GOVERNING LAW 

 This Plan and all Awards and actions taken thereunder shall be governed
by, and construed in accordance with, the laws of the State of Delaware, applied without regard to conflict of law principles. 
  

			
	DATE APPROVED BY BOARD OF DIRECTORS:	  	January 15, 2016
		
	DATE APPROVED BY STOCKHOLDERS:	  	[●], 2016

  
 19 

 INCENTIVE STOCK OPTION AGREEMENT 

UNDER THE PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

							
			
	Name of Optionee:	 	                                   
                                         
                   	  	
			
	No. of Option Shares:	 	                                   
                                         
                   	  	
			
	Option Exercise Price per Share:	 	$                                   
                                         
                 	  	
		 	[FMV on Grant Date (110% of FMV if a 10% owner)]
			
	Grant Date:	 	                                   
                                         
                   	  	
			
	Expiration Date:	 	                                   
                                         
                   	  	
		 	[up to 10 years (5 if a 10% owner)]	  	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants to the Optionee named above an option (the “Stock Option”) to purchase on or prior to the Expiration Date specified
above all or part of the number of shares of Common Stock, par value $0.001 per share (the “Stock”), of the Company specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth
herein and in the Plan. 
 1. Exercisability Schedule. No portion of this Stock Option may be exercised until such portion shall have
become exercisable. Except as set forth below, and subject to the discretion of the Administrator (as defined in Section 1 of the Plan) to accelerate the exercisability schedule hereunder, this Stock Option shall be exercisable with respect to
the following number of Option Shares on the dates indicated so long as the Optionee remains an employee of the Company or a Subsidiary on such dates: 
  

			
	 Incremental Number of

Option Shares Exercisable*
	  	Exercisability Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

  

	*	Max. of $100,000 per yr. 

 Once exercisable, this Stock Option shall continue to be exercisable
at any time or times prior to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan. 

 2. Manner of Exercise. 

(a) The Optionee may exercise this Stock Option only in the following manner: from time to time on or prior to the Expiration Date of this
Stock Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of shares of Stock that have been purchased by the Optionee on the open market or that are beneficially
owned by the Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; or (iii) by the Optionee delivering to the Company a properly
executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to
pay the option purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment
procedure; or (iv) a combination of (i), (ii) and (iii) above. Payment instruments will be received subject to collection. 

The transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the
Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above, (ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and
(iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require to satisfy itself that the issuance of Stock to be purchased pursuant to the exercise of Stock Options under the Plan and any subsequent
resale of the shares of Stock will be in compliance with applicable laws and regulations. In the event the Optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock
transferred to the Optionee upon the exercise of the Stock Option shall be net of the Shares attested to. 
 (b) The shares of Stock
purchased upon exercise of this Stock Option shall be transferred to the Optionee on the records of the Company or of the transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or
regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any shares of Stock subject to this Stock Option unless and until this Stock Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall have
transferred the shares to the Optionee, and the Optionee’s name shall have been entered as the stockholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with respect
to such shares of Stock. 

  
 2 

 (c) The minimum number of shares with respect to which this Stock Option may be exercised at any
one time shall be 100 shares, unless the number of shares with respect to which this Stock Option is being exercised is the total number of shares subject to exercise under this Stock Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date
hereof. 
 3. Termination of Employment. If the Optionee’s employment by the Company or a Subsidiary (as defined in the Plan) is
terminated, the period within which to exercise the Stock Option may be subject to earlier termination as set forth below. 
 (a)
Termination Due to Death. If the Optionee’s employment terminates by reason of the Optionee’s death, any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be
exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of death shall terminate
immediately and be of no further force or effect. 
 (b) Termination Due to Disability. If the Optionee’s employment terminates
by reason of the Optionee’s disability (as determined by the Administrator), any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of such termination of employment, may thereafter be exercised by the
Optionee for a period of 12 months from the date of disability or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of disability shall terminate immediately and be of no further force or
effect. 
 (c) Termination for Cause. If the Optionee’s employment terminates for Cause, any portion of this Stock Option
outstanding on such date shall terminate immediately and be of no further force and effect. For purposes hereof, “Cause” shall mean, unless otherwise provided in an employment agreement between the Company and the Optionee, a determination
by the Administrator that the Optionee shall be dismissed as a result of (i) any material breach by the Optionee of any agreement between the Optionee and the Company; (ii) the conviction of, indictment for or plea of nolo contendere by
the Optionee to a felony or a crime involving moral turpitude; or (iii) any material misconduct or willful and deliberate non-performance (other than by reason of disability) by the Optionee of the Optionee’s duties to the Company. 

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the
Optionee’s disability, or Cause, and unless otherwise determined by the Administrator, any portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three
months from the date of termination or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect. 

  
 3 

 The Administrator’s determination of the reason for termination of the Optionee’s
employment shall be conclusive and binding on the Optionee and his or her representatives or legatees. 
 4. Incorporation of Plan.
Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms
in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein. 
 5.
Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution. This Stock Option is
exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal representative or legatee. 

6. Status of the Stock Option. This Stock Option is intended to qualify as an “incentive stock option” under Section 422
of the Internal Revenue Code of 1986, as amended (the “Code”), but the Company does not represent or warrant that this Stock Option qualifies as such. The Optionee should consult with his or her own tax advisors regarding the tax
effects of this Stock Option and the requirements necessary to obtain favorable income tax treatment under Section 422 of the Code, including, but not limited to, holding period requirements. To the extent any portion of this Stock Option does
not so qualify as an “incentive stock option,” such portion shall be deemed to be a non-qualified stock option. If the Optionee intends to dispose or does dispose (whether by sale, gift, transfer or otherwise) of any Option Shares within
the one-year period beginning on the date after the transfer of such shares to him or her, or within the two-year period beginning on the day after the grant of this Stock Option, he or she will so notify the Company within 30 days after such
disposition. 
 7. Tax Withholding. The Optionee shall, not later than the date as of which the exercise of this Stock Option becomes
a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The
Company shall have the authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Optionee a number of shares of Stock with an aggregate Fair
Market Value that would satisfy the minimum withholding amount due. 
 8. No Obligation to Continue Employment. Neither the Company
nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate
the employment of the Optionee at any time. 
 9. Integration. This Agreement constitutes the entire agreement between the parties
with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 

  
 4 

 10. Data Privacy Consent. In order to administer the Plan and this Agreement and to
implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not
limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant
Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Optionee may
have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the
Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law. 

11. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or
delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                     	 		 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 5 

 NON-QUALIFIED STOCK OPTION AGREEMENT 

FOR COMPANY EMPLOYEES 

UNDER PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

							
			
	Name of Optionee:	 	                                   
                                         
                   	  	
			
	No. of Option Shares:	 	                                   
                                         
                   	  	
			
	Option Exercise Price per Share:	 	$                                   
                                         
                 	  	
		 	[FMV on Grant Date]
			
	Grant Date:	 	                                   
                                         
                   	  	
			
	Expiration Date:	 	                                   
                                         
                   	  	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants to the Optionee named above an option (the “Stock Option”) to purchase on or prior to the Expiration Date specified
above all or part of the number of shares of Common Stock, par value $0.001 per share (the “Stock”) of the Company specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth
herein and in the Plan. This Stock Option is not intended to be an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as amended. 

1. Exercisability Schedule. No portion of this Stock Option may be exercised until such portion shall have become exercisable. Except
as set forth below, and subject to the discretion of the Administrator (as defined in Section 1 of the Plan) to accelerate the exercisability schedule hereunder, this Stock Option shall be exercisable with respect to the following number of
Option Shares on the dates indicated so long as Optionee remains an employee of the Company or a Subsidiary on such dates: 
  

			
	 Incremental Number of

Option Shares Exercisable
	  	Exercisability Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

 Once exercisable, this Stock Option shall continue to be exercisable at any time or times prior to the close
of business on the Expiration Date, subject to the provisions hereof and of the Plan. 

 2. Manner of Exercise. 

(a) The Optionee may exercise this Stock Option only in the following manner: from time to time on or prior to the Expiration Date of this
Stock Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of shares of Stock that have been purchased by the Optionee on the open market or that are beneficially
owned by the Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; (iii) by the Optionee delivering to the Company a properly
executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to
pay the option purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment
procedure; (iv) by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the
aggregate exercise price; or (v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection. 

The transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the
Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above, (ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and
(iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require to satisfy itself that the issuance of Stock to be purchased pursuant to the exercise of Stock Options under the Plan and any subsequent
resale of the shares of Stock will be in compliance with applicable laws and regulations. In the event the Optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock
transferred to the Optionee upon the exercise of the Stock Option shall be net of the Shares attested to. 
 (b) The shares of Stock
purchased upon exercise of this Stock Option shall be transferred to the Optionee on the records of the Company or of the transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or
regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any shares of Stock subject to this Stock Option unless and until this Stock Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall have
transferred the shares to the Optionee, and the Optionee’s name shall have been entered as the stockholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with respect
to such shares of Stock. 

  
 2 

 (c) The minimum number of shares with respect to which this Stock Option may be exercised at any
one time shall be 100 shares, unless the number of shares with respect to which this Stock Option is being exercised is the total number of shares subject to exercise under this Stock Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date
hereof. 
 3. Termination of Employment. If the Optionee’s employment by the Company or a Subsidiary (as defined in the Plan) is
terminated, the period within which to exercise the Stock Option may be subject to earlier termination as set forth below. 
 (a)
Termination Due to Death. If the Optionee’s employment terminates by reason of the Optionee’s death, any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be
exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of death shall terminate
immediately and be of no further force or effect. 
 (b) Termination Due to Disability. If the Optionee’s employment terminates
by reason of the Optionee’s disability (as determined by the Administrator), any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of such termination of employment, may thereafter be exercised by the
Optionee for a period of 12 months from the date of disability or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of disability shall terminate immediately and be of no further force or
effect. 
 (c) Termination for Cause. If the Optionee’s employment terminates for Cause, any portion of this Stock Option
outstanding on such date shall terminate immediately and be of no further force and effect. For purposes hereof, “Cause” shall mean, unless otherwise provided in an employment agreement between the Company and the Optionee, a determination
by the Administrator that the Optionee shall be dismissed as a result of (i) any material breach by the Optionee of any agreement between the Optionee and the Company; (ii) the conviction of, indictment for or plea of nolo contendere by
the Optionee to a felony or a crime involving moral turpitude; or (iii) any material misconduct or willful and deliberate non-performance (other than by reason of disability) by the Optionee of the Optionee’s duties to the Company. 

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the
Optionee’s disability or Cause, and unless otherwise determined by the Administrator, any portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three months
from the date of termination or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect. 

  
 3 

 The Administrator’s determination of the reason for termination of the Optionee’s
employment shall be conclusive and binding on the Optionee and his or her representatives or legatees. 
 4. Incorporation of Plan.
Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms
in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein. 
 5.
Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution. This Stock Option is
exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal representative or legatee. 

6. Tax Withholding. The Optionee shall, not later than the date as of which the exercise of this Stock Option becomes a taxable event
for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the
authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Optionee a number of shares of Stock with an aggregate Fair Market Value that would
satisfy the minimum withholding amount due. 
 7. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is
obligated by or as a result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the
Optionee at any time. 
 8. Integration. This Agreement constitutes the entire agreement between the parties with respect to this
Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 9. Data Privacy
Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may
process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the
administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all
Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and
(iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will
only be used in accordance with applicable law. 

  
 4 

 10. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                     	 		 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 5 

 NON-QUALIFIED STOCK OPTION AGREEMENT 

FOR NON-EMPLOYEE DIRECTORS 

UNDER PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

							
			
	Name of Optionee:	 	                                   
                                         
                   	  	
			
	No. of Option Shares:	 	                                   
                                         
                   	  	
			
	Option Exercise Price per Share:	 	$                                   
                                         
                 	  	
		 	[FMV on Grant Date]
			
	Grant Date:	 	                                   
                                         
                   	  	
			
	Expiration Date:	 	                                   
                                         
                   	  	
		 	[No more than 10 years]	  	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants to the Optionee named above, who is a Director of the Company but is not an employee of the Company, an option (the “Stock
Option”) to purchase on or prior to the Expiration Date specified above all or part of the number of shares of Common Stock, par value $0.001 per share (the “Stock”), of the Company specified above at the Option Exercise
Price per Share specified above subject to the terms and conditions set forth herein and in the Plan. This Stock Option is not intended to be an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as
amended. 
 1. Exercisability Schedule. No portion of this Stock Option may be exercised until such portion shall have become
exercisable. Except as set forth below, and subject to the discretion of the Administrator (as defined in Section 1 of the Plan) to accelerate the exercisability schedule hereunder, this Stock Option shall be exercisable with respect to the
following number of Option Shares on the dates indicated so long as the Optionee remains in service as a member of the Board on such dates: 
  

			
	 Incremental Number of

Option Shares Exercisable
	  	Exercisability Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

 Once exercisable, this Stock Option shall continue to be exercisable at any time or times prior
to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan. 
 2. Manner of Exercise. 

(a) The Optionee may exercise this Stock Option only in the following manner: from time to time on or prior to the Expiration Date of this
Stock Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be
purchased. 
 Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by
certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of shares of Stock that have been purchased by the Optionee on the open market or that are beneficially
owned by the Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; (iii) by the Optionee delivering to the Company a properly
executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to
pay the option purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment
procedure; (iv) by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the
aggregate exercise price; or (v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection. 

The transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the
Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above, (ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and
(iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require to satisfy itself that the issuance of Stock to be purchased pursuant to the exercise of Stock Options under the Plan and any subsequent
resale of the shares of Stock will be in compliance with applicable laws and regulations. In the event the Optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock
transferred to the Optionee upon the exercise of the Stock Option shall be net of the Shares attested to. 
 (b) The shares of Stock
purchased upon exercise of this Stock Option shall be transferred to the Optionee on the records of the Company or of the transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or
regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder
of, or to have any of the rights of a 

  
 2 

 
holder with respect to, any shares of Stock subject to this Stock Option unless and until this Stock Option shall have been exercised pursuant to the terms hereof, the Company or the transfer
agent shall have transferred the shares to the Optionee, and the Optionee’s name shall have been entered as the stockholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership
rights with respect to such shares of Stock. 
 (c) The minimum number of shares with respect to which this Stock Option may be exercised at
any one time shall be 100 shares, unless the number of shares with respect to which this Stock Option is being exercised is the total number of shares subject to exercise under this Stock Option at the time. 

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date
hereof. 
 3. Termination as Director. If the Optionee ceases to be a Director of the Company, the period within which to exercise
the Stock Option may be subject to earlier termination as set forth below. 
 (a) Termination Due to Death. If the Optionee’s
service as a Director terminates by reason of the Optionee’s death, any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be exercised by the Optionee’s legal
representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of death shall terminate immediately and be of no further force
or effect. 
 (b) Other Termination. If the Optionee ceases to be a Director for any reason other than the Optionee’s death, any
portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date the Optionee ceased to be a Director, for a period of six months from the date the Optionee ceased to be a Director or until the Expiration
Date, if earlier. Any portion of this Stock Option that is not exercisable on the date the Optionee ceases to be a Director shall terminate immediately and be of no further force or effect. 

4. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all
the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified
herein. 
 5. Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner,
by operation of law or otherwise, other than by will or the laws of descent and distribution. This Stock Option is exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal
representative or legatee. 
 6. No Obligation to Continue as a Director. Neither the Plan nor this Stock Option confers upon the
Optionee any rights with respect to continuance as a Director. 

  
 3 

 7. Integration. This Agreement constitutes the entire agreement between the parties with
respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 8.
Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant
Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or
desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant
Companies all Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes
the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in
accordance with applicable law. 

  
 4 

 9. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal
place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                     	 		 		 	  

		 		 		 	Optionee’s Signature
				
		 		 		 	Optionee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 5 

 RESTRICTED STOCK AWARD AGREEMENT 

UNDER THE PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

					
	Name of Grantee:	 	  
	  	
			
	No. of Shares:	 	  
	  	
			
	Grant Date:	 	  
	  	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants a Restricted Stock Award (an “Award”) to the Grantee named above. Upon acceptance of this Award, the Grantee shall
receive the number of shares of Common Stock, par value $0.001 per share (the “Stock”) of the Company specified above, subject to the restrictions and conditions set forth herein and in the Plan. The Company acknowledges the receipt
from the Grantee of consideration with respect to the par value of the Stock in the form of cash, past or future services rendered to the Company by the Grantee or such other form of consideration as is acceptable to the Administrator. 

1. Award. The shares of Restricted Stock awarded hereunder shall be issued and held by the Company’s transfer agent in book entry
form, and the Grantee’s name shall be entered as the stockholder of record on the books of the Company. Thereupon, the Grantee shall have all the rights of a stockholder with respect to such shares, including voting and dividend rights,
subject, however, to the restrictions and conditions specified in Paragraph 2 below. The Grantee shall (i) sign and deliver to the Company a copy of this Award Agreement and (ii) deliver to the Company a stock power endorsed in blank.

 2. Restrictions and Conditions. 

(a) Any book entries for the shares of Restricted Stock granted herein shall bear an appropriate legend, as determined by the Administrator in
its sole discretion, to the effect that such shares are subject to restrictions as set forth herein and in the Plan. 
 (b) Shares of
Restricted Stock granted herein may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of by the Grantee prior to vesting. 

(c) If the Grantee’s employment with the Company and its Subsidiaries is voluntarily or involuntarily terminated for any reason
(including death) prior to vesting of shares of Restricted Stock granted herein, all shares of Restricted Stock shall immediately and automatically be forfeited and returned to the Company. 

3. Vesting of Restricted Stock. The restrictions and conditions in Paragraph 2 of this Agreement shall lapse on the Vesting Date or
Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series 

 
of Vesting Dates is specified, then the restrictions and conditions in Paragraph 2 shall lapse only with respect to the number of shares of Restricted Stock specified as vested on such date. 

 

			
	 Incremental Number

of Shares Vested
	  	Vesting Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

 Subsequent to such Vesting Date or Dates, the shares of Stock on which all restrictions and conditions have
lapsed shall no longer be deemed Restricted Stock. The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 3. 

4. Dividends. Dividends on shares of Restricted Stock shall be paid currently to the Grantee. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Award shall be subject to and governed by all the terms
and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein. 

6. Transferability. This Agreement is personal to the Grantee, is non-assignable and is not transferable in any manner, by operation of
law or otherwise, other than by will or the laws of descent and distribution. 
 7. Tax Withholding. The Grantee shall, not later
than the date as of which the receipt of this Award becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law
to be withheld on account of such taxable event. Except in the case where an election is made pursuant to Paragraph 8 below, the Company shall have the authority to cause the required minimum tax withholding obligation to be satisfied, in whole or
in part, by withholding from shares of Stock to be issued or released by the transfer agent a number of shares of Stock with an aggregate Fair Market Value that would satisfy the minimum withholding amount due. 

8. Election Under Section 83(b). The Grantee and the Company hereby agree that the Grantee may, within 30 days following the Grant
Date of this Award, file with the Internal Revenue Service and the Company an election under Section 83(b) of the Internal Revenue Code. In the event the Grantee makes such an election, he or she agrees to provide a copy of the election to the
Company. The Grantee acknowledges that he or she is responsible for obtaining the advice of his or her tax advisors with regard to the Section 83(b) election and that he or she is relying solely on such advisors and not on any statements or
representations of the Company or any of its agents with regard to such election. 

  
 2 

 9. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is
obligated by or as a result of the Plan or this Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the
Grantee at any time. 
 10. Integration. This Agreement constitutes the entire agreement between the parties with respect to this
Award and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 11. Data Privacy
Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may
process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the
administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all
Relevant Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes
the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in
accordance with applicable law. 

  
 3 

 12. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                     	 		 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 4 

 RESTRICTED STOCK UNIT AWARD AGREEMENT 

FOR COMPANY EMPLOYEES 

UNDER PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

					
	Name of Grantee:	 	  
	 	
			
	No. of Restricted Stock Units:	 	  
	 	
			
	Grant Date:	 	  
	 	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants an award of the number of Restricted Stock Units listed above (an “Award”) to the Grantee named above. Each
Restricted Stock Unit shall relate to one share of Common Stock, par value $0.001 per share (the “Stock”) of the Company. 

1. Restrictions on Transfer of Award. This Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of
by the Grantee, and any shares of Stock issuable with respect to the Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of until (i) the Restricted Stock Units have vested as provided in Paragraph 2 of
this Agreement and (ii) shares of Stock have been issued to the Grantee in accordance with the terms of the Plan and this Agreement. 

2. Vesting of Restricted Stock Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting
Date or Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall
lapse only with respect to the number of Restricted Stock Units specified as vested on such date. 
  

			
	 Incremental Number of

Restricted Stock Units Vested
	  	Vesting Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

 The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2. 

3. Termination of Employment. If the Grantee’s employment with the Company and its Subsidiaries terminates for any reason
(including death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Stock Units that have not vested as of such date shall automatically and without notice terminate and be forfeited,
and neither the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Stock Units. 

 4. Issuance of Shares of Stock. As soon as practicable following each Vesting Date (but in
no event later than two and one-half months after the end of the year in which the Vesting Date occurs), the Company shall issue to the Grantee the number of shares of Stock equal to the aggregate number of Restricted Stock Units that have vested
pursuant to Paragraph 2 of this Agreement on such date and the Grantee shall thereafter have all the rights of a stockholder of the Company with respect to such shares. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Agreement shall be subject to and governed by all the
terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

 6. Tax Withholding. The Grantee shall, not later than the date as of which the receipt of this Award becomes a taxable event for
Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the
authority to cause the required minimum tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Grantee a number of shares of Stock with an aggregate Fair Market Value that would
satisfy the withholding amount due. 
 7. Section 409A of the Code. This Agreement shall be interpreted in such a manner that
all provisions relating to the settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code. 

8. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this
Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Grantee at any time. 

9. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Award and supersedes all prior
agreements and discussions between the parties concerning such subject matter. 
 10. Data Privacy Consent. In order to administer
the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or
professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this
Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any
privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; 

  
 2 

 
and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to
change, the Relevant Information. Relevant Information will only be used in accordance with applicable law. 
 11. Notices. Notices
hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently
furnish to the other party in writing. 
  

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                    	 		 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 3 

 RESTRICTED STOCK UNIT AWARD AGREEMENT 

FOR NON-EMPLOYEE DIRECTORS 

UNDER PROTEOSTASIS THERAPEUTICS, INC. 

2016 STOCK OPTION AND INCENTIVE PLAN 
  

					
			
	Name of Grantee:	 	  
	 	
			
	No. of Restricted Stock Units:	 	  
	 	
			
	Grant Date:	 	  
	 	

 Pursuant to the Proteostasis Therapeutics, Inc. 2016 Stock Option and Incentive Plan (as amended from time to
time, the “Plan”), Proteostasis Therapeutics, Inc. (the “Company”) hereby grants an award of the number of Restricted Stock Units listed above (an “Award”) to the Grantee named above. Each
Restricted Stock Unit shall relate to one share of Common Stock, par value $0.001 per share (the “Stock”) of the Company. 

1. Restrictions on Transfer of Award. This Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of
by the Grantee, and any shares of Stock issuable with respect to the Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of until (i) the Restricted Stock Units have vested as provided in Paragraph 2 of
this Agreement and (ii) shares of Stock have been issued to the Grantee in accordance with the terms of the Plan and this Agreement. 

2. Vesting of Restricted Stock Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting
Date or Dates specified in the following schedule so long as the Grantee remains in service as a member of the Board on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall lapse only
with respect to the number of Restricted Stock Units specified as vested on such date. 
  

			
	 Incremental Number of

Restricted Stock Units Vested
	  	Vesting Date
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    
	                     
(    %)
	  	                    

 The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2. 

3. Termination of Service. If the Grantee’s service with the Company and its Subsidiaries terminates for any reason (including
death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Stock Units that have not vested as of such date shall automatically and without notice terminate and be forfeited, and neither
the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Stock Units. 

 4. Issuance of Shares of Stock. As soon as practicable following each Vesting Date (but in
no event later than two and one-half months after the end of the year in which the Vesting Date occurs), the Company shall issue to the Grantee the number of shares of Stock equal to the aggregate number of Restricted Stock Units that have vested
pursuant to Paragraph 2 of this Agreement on such date and the Grantee shall thereafter have all the rights of a stockholder of the Company with respect to such shares. 

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Agreement shall be subject to and governed by all the
terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

 6. Section 409A of the Code. This Agreement shall be interpreted in such a manner that all provisions relating to the
settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code. 

7. No Obligation to Continue as a Director. Neither the Plan nor this Award confers upon the Grantee any rights with respect to
continuance as a Director. 
 8. Integration. This Agreement constitutes the entire agreement between the parties with respect to
this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter. 
 9. Data Privacy
Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may
process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the
administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all
Relevant Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes
the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in
accordance with applicable law. 

  
 2 

 10. Notices. Notices hereunder shall be mailed or delivered to the Company at its
principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing. 

 

							
		 		 	PROTEOSTASIS THERAPEUTICS, INC.
				
		 		 	By:	 	  

		 		 	Title:	 	

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned.
Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable. 
  

							
	Dated:                     	 		 		 	  

		 		 		 	Grantee’s Signature
				
		 		 		 	Grantee’s name and address:
				
		 		 		 	  

		 		 		 	  

		 		 		 	  

  
 3

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