Document:

<PAGE>
                                                                     Exhibit 4.2

                                                                  EXECUTION COPY

                           ALTUS PHARMACEUTICALS INC.

               AMENDED AND RESTATED STOCKHOLDERS' VOTING AGREEMENT

This Amended and Restated Stockholders' Voting Agreement (this "Agreement")
dated as of May 21, 2004 is entered into by and among Altus Pharmaceuticals
Inc., a Delaware corporation (the "Company") (f/k/a "Altus Biologics Inc."),
Nomura International plc ("Nomura"), U.S. Venture Partners VIII, L.P. ("USVP"),
USVP VIII Affiliates Fund, L.P., USVP Entrepreneur Partners Fund VIII-A, L.P.,
USVP Entrepreneur Partners Fund VIII-B, L.P. (collectively, the "USVP
Affiliates"), and the other persons and entities listed on Exhibit A hereto
(each individually, a "Purchaser" and collectively, the "Purchasers"), and
Vertex Pharmaceuticals Incorporated, a Massachusetts corporation ("Vertex"), and
amends and restates that certain Stockholders' Voting Agreement among the
Company and the parties thereto, dated as of September 26, 2001, as amended as
of December 7, 2001 (the "Prior Agreement"). Each of Nomura, USVP and the USVP
Affiliates is one of the entities listed on Exhibit A and is therefore included
within the definition of "Purchaser" and "Purchasers." The Purchasers and Vertex
are sometimes referred to in this Agreement collectively as the "Stockholders."

                                    Recitals:

     1. Vertex owns certain outstanding shares of common stock, $.01 par value
per share, of the Company (the "Common Stock"), warrants to purchase shares of
Common Stock, shares of Series A Convertible Preferred Stock, $.01 par value per
share, of the Company (the "Series A Preferred Stock"), and shares of Redeemable
Preferred Stock, $.01 par value per share, of the Company;

     2. Certain of the Purchasers are purchasing, concurrently herewith, shares
of Series C Convertible Preferred Stock, $.01 par value per share, of the
Company (the "Series C Preferred Stock") and warrants to purchase shares of
Series C Preferred Stock pursuant to the Series C Convertible Preferred Stock
and Warrant Purchase Agreement of even date herewith by and among the Company
and such Purchasers (the "Purchase Agreement");

     3. The Company, Vertex and certain of the Purchasers are parties to the
Prior Agreement;

     4. The undersigned parties represent the necessary voting power in order to
amend the Prior Agreement as set forth in Section 7(e) thereof; and

     5. The Purchasers and Vertex wish to provide for their continuing
representation on the Board of Directors of the Company (the "Board") in the
manner set forth below.

     In consideration of the mutual covenants contained herein and the
consummation of the sale and purchase of shares of capital stock of the Company
pursuant to the Purchase Agreement, and for other valuable consideration,
receipt of which is hereby acknowledged, the parties hereto agree as follows:
<PAGE>
     1. Voting of Shares.

               (a) In any and all elections of directors of the Company (whether
     at a meeting or by written consent in lieu of a meeting), each Stockholder
     shall vote or cause to be voted all Shares (as defined in Section 2 below)
     owned by him, her or it, or over which he, she or it has voting control,
     and otherwise use his, her or its respective best efforts, so as to fix the
     number of directors of the Company at nine (9) and to elect to the Board as
     directors (i) one (1) member designated by Nomura, (ii) one (1) member
     designated by USVP, (iii) one (1) member designated by Vertex, (iv) two (2)
     members designated by the holders of a majority of the outstanding shares
     of Series C Preferred Stock, (v) the Company's Chief Executive Officer and
     (vi) three (3) members, who shall not be employed by the Company,
     designated by not less than 3 of the Series B Directors and Series C
     Directors (as defined below) (the "Outside Directors"). The directors
     designated by the holders of a majority of the outstanding shares of Series
     C Preferred Stock shall be the Series C Directors (as defined in the
     Company's Third Amended and Restated Certificate of Incorporation, as
     amended (the "Charter")), the directors designated by Nomura and USVP shall
     be the Series B Directors (as defined in the Charter) and the director
     designated by Vertex shall be the Series A Director (as defined in the
     Charter). As of the date hereof, the directors designated by the holders of
     a majority of the outstanding shares of Series C Preferred Stock shall be
     Stewart Hen and Jonathan Leff, the director designated by Nomura shall be
     John Richard, the director designated by USVP shall be Jonathan Root, the
     director designated by Vertex shall be Lynne Brum, the Company's Chief
     Executive Officer is Peter Lanciano, and the three (3) Outside Directors
     shall be Manuel Navia, Richard Aldrich and Michael Wyzga.

               (b) In the event that any director designated in the manner set
     forth in Section 1(a) above is unable to serve, or once having commenced to
     serve, is removed or withdraws from the Board (a "Withdrawing Director"),
     such Withdrawing Director's replacement (the "Substitute Director") will be
     designated by the Stockholder or Stockholders or members of the Board, as
     the case may be, with the right to designate the Withdrawing Director or
     Directors being replaced; provided, however, in the case of the Company's
     Chief Executive Officer, the Substitute Director shall be the successor to
     the Company's Chief Executive Officer. Each Stockholder agrees to take all
     action within its respective power, including, but not limited to, the
     voting of all Shares owned by him, her or it, (i) to cause the election of
     such Substitute Director promptly following his or her nomination pursuant
     to this Section 1(b), and (ii) upon the written request of the Stockholder
     or Stockholders or members of the Board, as the case may be, with the right
     to designate a director or directors pursuant to Section 1(a) above, to
     remove, with or without cause, the respective director or directors
     designated by such Stockholder or Stockholders or members of the Board, as
     the case may be.

               (c) The Stockholders shall not vote to remove any director
     designated pursuant to Section 1(a)(i)-(iv) above without the consent of
     the Stockholder or Stockholders with the right to designate such director,
     except in the case of removal for bad faith or willful misconduct. No
     Stockholders shall vote to remove (i) the Company's Chief Executive Officer
     as director so long as such person holds such position with the Company or
     (ii) any Outside Director without the consent of not less than three (3) of
     the

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     Series B Directors and Series C Directors, excluding the director or
     directors subject to removal, except, in both instances, in the case of
     removal for bad faith or willful misconduct.

               (d) The Company shall provide a written notice (a "Designating
     Party Notice") to the Stockholders at least 30 days prior to sending a
     notice to stockholders for a meeting at which directors are to be elected
     (an "Election Notice"). A Designating Party Notice shall state the date
     (the "Mailing Date") upon which the respective Election Notice is to be
     mailed to stockholders. The Mailing Date shall be a date that is at least
     15 days after the date the Designation Party Notice is delivered to the
     Stockholders. The holders of a majority of the outstanding shares of Series
     C Preferred Stock, Nomura, USVP, Vertex and the Board shall each give
     written notice to all other parties to this Agreement, no later than five
     (5) days prior to the Mailing Date, of the persons designated pursuant to
     Section 1(a) as nominees for election as directors; provided, however, so
     long as a Stockholder, initially to be Warburg Pincus Private Equity VIII,
     L.P. ("Warburg Pincus") (together with its affiliates), holds a majority of
     the outstanding shares of Series C Preferred Stock, such Stockholder shall
     provide all such notices on behalf of the holders of a majority of the
     outstanding Series C Preferred Stock as may be required by this Section
     1(d). The Company agrees to nominate and recommend for election as
     directors only those individuals designated, or to be designated, pursuant
     to Section 1(a) above. If Nomura, USVP, Vertex or the holders of a majority
     of the outstanding shares of Series C Preferred Stock shall fail to give
     notice to the Company as provided above, the designees of such Stockholders
     who failed to give such notice then serving as directors shall be deemed
     the designees for reelection.

               (e) In the event that the member designated by Nomura is unable
     to attend any duly noticed meeting of the Board, the Company shall allow an
     observer designated by Nomura to attend such meeting.

               (f) For so long as he serves as an officer of the Company, Alexey
     Margolin shall have the right to receive due notice of all meetings of the
     Board and to attend all such meetings as an observer.

     2. Shares. "Shares" shall mean and include any and all shares of Common
Stock and/or shares of capital stock of the Company, by whatever name called,
which carry voting rights (including voting rights which arise by reason of
default or by receipt of a proxy from another shareholder of the Company) and
shall include any such shares now owned or subsequently acquired by a
Stockholder, however acquired, including without limitation stock splits and
stock dividends.

     3. Termination.

               (a) All rights and obligations of Nomura under this Agreement
     shall terminate on the date on which Nomura no longer holds at least thirty
     percent (30%) of the shares of the Company's Series B Convertible Preferred
     Stock, $.01 par value per share (the "Series B Preferred Stock"), purchased
     by Nomura in accordance with the Series B Convertible Preferred Stock and
     Warrant Purchase Agreement dated September

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     26, 2001, by and among the Company and certain Purchasers, as amended (the
     "Series B Purchase Agreement") (subject to appropriate adjustment for stock
     splits, stock dividends, recapitalizations and other similar events).

               (b) All rights and obligations of USVP under this Agreement shall
     terminate on the date on which USVP and the USVP Affiliates, in the
     aggregate, no longer hold at least thirty percent (30%) of the shares of
     the Series B Preferred Stock purchased by USVP and the USVP Affiliates in
     accordance with the terms of the Series B Purchase Agreement (subject to
     appropriate adjustment for stock splits, stock dividends, recapitalizations
     and other similar events).

               (c) All rights and obligations of Vertex under this Agreement
     shall terminate on the date on which Vertex no longer holds at least thirty
     percent (30%) of the shares of Series A Preferred Stock held by Vertex on
     the date of this Agreement (subject to appropriate adjustment for stock
     splits, stock dividends, recapitalizations and other similar events).

               (d) All rights and obligations of the holders of a majority of
     the outstanding shares of Series C Preferred Stock under this Agreement
     shall terminate on the date on which less than thirty-five percent (35%) of
     the total number of shares of Series C Preferred Stock purchased pursuant
     to the Purchase Agreement remains outstanding (subject to appropriate
     adjustment for stock splits, stock dividends, recapitalizations and other
     similar events).

               (e) This Agreement shall terminate in its entirety on the
     earliest of (i) the closing of the Company's initial firm commitment
     underwritten public offering of shares of Common Stock pursuant to an
     effective registration statement under the Securities Act of 1933, as
     amended (the "Act"), resulting in at least $50 million of net proceeds to
     the Company at a minimum price to the public of $6.4721037 per share
     (subject to appropriate adjustment for stock splits, stock dividends,
     recapitalizations and other similar events) (a "Qualified Public
     Offering"), or (ii) the sale of all or substantially all of the assets or
     business of the Company, by merger, sale of assets or otherwise.

     4. No Revocation. The voting agreements contained herein are coupled with
an interest and may not be revoked, except by an amendment, modification or
termination effected in accordance with Section 3 or 7(f) hereof. Nothing in
this Section 4 shall be construed as limiting the provisions of Section 3 or
7(f) hereof.

     5. Restrictive Legend. All certificates representing Shares owned or
hereafter acquired by the Stockholders or any transferee of the Stockholders
bound by this Agreement shall have affixed thereto a legend substantially in the
following form:

          "The shares of stock represented by this certificate are subject to
          certain voting agreements as set forth in an Amended and Restated
          Stockholders' Voting Agreement, as amended from time to time, by and
          among the registered owner of this certificate, the Company and
          certain other stockholders of the Company, a copy of which is

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<PAGE>
          available for inspection at the offices of the Secretary of the
          Company."

     6. Transfers of Rights. Any transferee to whom Shares are transferred by a
Stockholder, whether voluntarily or by operation of law, shall be bound by the
voting obligations imposed upon the transferor under this Agreement, to the same
extent as if such transferee were a Stockholder hereunder and no Stockholder
shall transfer any Shares unless the transferee agrees in writing to be bound by
this Agreement.

     7. General.

               (a) Severability. The invalidity or unenforceability of any
     provision of this Agreement shall not affect the validity or enforceability
     of any other provision of this Agreement.

               (b) Rights of Purchasers. Each Purchaser shall have the absolute
     right to exercise or refrain from exercising any right or rights that such
     Purchaser may have by reason of this Agreement including without
     limitation, the right to consent to the waiver of any obligation of the
     Company and to enter into an agreement with the Company for the purpose of
     modifying this Agreement. Each such Purchaser shall not incur any liability
     to any other Purchaser with respect to exercising or refraining from
     exercising any such right or rights that such Purchaser may have by reason
     of this Agreement.

               (c) Specific Performance. In addition to any and all other
     remedies that may be available at law in the event of any breach of this
     Agreement, each Purchaser shall be entitled to specific performance of the
     agreements and obligations of the Stockholders hereunder and to such other
     injunctive or other equitable relief as may be granted by a court of
     competent jurisdiction.

               (d) Governing Law. This Agreement shall be governed by and
     construed in accordance with the internal laws of the State of Delaware
     (without reference to the conflicts of law provisions thereof).

               (e) Notices. All notices, requests, consents, and other
     communications under this Agreement shall be in writing and shall be deemed
     delivered (i) two (2) business days after being sent by registered or
     certified mail, return receipt requested, postage prepaid or (ii) one (1)
     business day after being sent via a reputable nationwide overnight courier
     service guaranteeing next business day delivery, in each case to the
     intended recipient as set forth below:

     If to the Company, at 125 Sidney Street, Cambridge, Massachusetts 02139,
Attention: President, or at such other address or addresses as may have been
furnished in writing by the Company to the Purchasers and Vertex, with a copy to
Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., One Financial Center,
Boston, Massachusetts 02111, Attention: Jonathan L. Kravetz, Esq.; or

     If to a Purchaser, at the address set forth on Exhibit A for such
Purchaser, or at such other address or addresses as may have been furnished to
the Company and Vertex in writing by such

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<PAGE>
Purchaser. If the Purchaser is a holder of Series B Preferred Stock, a copy of
such notice shall be delivered to Tomlinson Zisko LLP, 200 Page Mill Road,
Second Floor, Palo Alto, California 94306, Attention: Jill E. Fishbein, Esq.,
and if the Purchaser is a holder of Series C Preferred Stock, a copy of such
notice shall be delivered to Willkie Farr & Gallagher LLP, 787 Seventh Avenue,
New York, New York 10019, Attention: Steven J. Gartner, Esq.; or

     If to Vertex, at 130 Waverly Street, Cambridge, Massachusetts 02139,
Attention: General Counsel, or at such other address or addresses as may have
been furnished in writing by Vertex to the Company and the Purchasers.

     Any party may give any notice, request, consent or other communication
under this Agreement using any other means (including, without limitation,
personal delivery, messenger service, telecopy, first class mail or electronic
mail), but no such notice, request, consent or other communication shall be
deemed to have been duly given unless and until it is actually received by the
party for whom it is intended. Any party may change the address to which
notices, requests, consents or other communications hereunder are to be
delivered by giving the other parties notice in the manner set forth in this
Section.

               (f) Complete Agreement; Amendments. This Agreement constitutes
     the entire agreement and understanding of the parties hereto with respect
     to the subject matter hereof, and supersedes all prior agreements and
     understandings relating to such subject matter. No amendment or termination
     of, or waiver under, any provision of this Agreement shall be valid unless
     in writing and signed by Stockholders holding at least fifty-five percent
     (55%) of the voting power of the Shares (on an as converted basis) then
     held by all Stockholders and the Company, and any such amendment,
     termination or waiver shall be binding on all parties hereto even if they
     do not execute such consent; provided, however, if any such amendment would
     affect the rights of a Stockholder or Stockholders or their respective
     directors to designate a director pursuant to Section 1 hereof, then in
     addition to the aforementioned consent described above, the written consent
     of such affected Stockholder or Stockholders shall also be required to
     enforce such amendment against such Stockholder or it or his designated
     director; provided further, that if any such amendment would otherwise
     affect the rights of the holders of any class or series of the Company's
     capital stock in a fashion different from the holders of any other class or
     series of the Company's capital stock, then, in addition to the
     aforementioned consent of fifty-five percent (55%) of the voting power of
     the Shares (on an as converted basis), the written consent of the holders
     of a majority of the voting power (on an as converted basis) of such class
     or series of the Company's capital stock held by such affected Stockholder
     or Stockholders shall also be required to enforce such amendment against
     such Stockholder. The Company shall give prompt written notice of any
     amendment or termination hereof or waiver hereunder to any party hereto
     that did not consent in writing to such amendment, termination or waiver.
     Solely for the purposes of this Section 7(f), Shares shall not include
     Common Stock issuable pursuant to either Article FOURTH, Section E.1.(c) or
     Section F.1.(c) of the Company's Certificate of Incorporation, as amended
     from time to time.

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               (g) Pronouns. Whenever the context may require, any pronouns used
     in this Agreement shall include the corresponding masculine, feminine or
     neuter forms, and the singular form of nouns and pronouns shall include the
     plural, and vice versa.

               (h) Counterparts; Facsimile Signatures. This Agreement may be
     executed in any number of counterparts, each of which shall be deemed to be
     an original, and all of which together shall constitute one and the same
     document. This Agreement may be executed by facsimile signatures.

               (i) Section Headings. The section headings are for the
     convenience of the parties and in no way alter, modify, amend, limit or
     restrict the contractual obligations of the parties.

               (j) Attorney's Fees. If any action at law or in equity (including
     arbitration) is instituted to enforce or interpret the terms of this
     Agreement, the prevailing party shall be entitled to reasonable attorney's
     fees, costs and necessary disbursements in addition to any other relief to
     which such party may be entitled.

                  [Remainder of Page Intentionally Left Blank]

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<PAGE>
Executed as of the date first written above.

                                       COMPANY:

                                       ALTUS PHARMACEUTICALS INC.

                                       By: /s/ Peter L. Lanciano
                                           -------------------------------------
                                       Name: Peter L. Lanciano
                                       Title: President and CEO

                                       VERTEX PHARMACEUTICALS INCORPORATED

                                       By: /s/ Kenneth S. Boger
                                           -------------------------------------
                                       Name: Kenneth S. Boger
                                             -----------------------------------
                                       Title: Sr. Vice President and General
                                              Counsel
                                              ----------------------------------

                                       NOMURA INTERNATIONAL PLC

                                       By: /s/ Denise Pollard-Knight
                                           -------------------------------------
                                       Name: Denise Pollard-Knight
                                             -----------------------------------
                                       Title: Head of Nomura Phase 4 Ventures
                                              ----------------------------------

                                       U.S. VENTURE PARTNERS VIII, L.P.
                                       USVP VIII AFFILIATES FUND, L.P.
                                       USVP ENTREPRENEUR PARTNERS VIII-A, L.P.
                                       USVP ENTREPRENEUR PARTNERS VIII-B, L.P.

                                       By Presidio Management Group VIII, L.L.C.
                                       The General Partner of Each

                                       By: /s/ Michael P. Maher
                                           -------------------------------------
                                       Name: Michael P. Maher
                                       Title: Attorney In-Fact

                                       CMEA VENTURES LIFE SCIENCES 2000, L.P

                                       By: /s/ Thomas R. Baruch
                                           -------------------------------------
                                       Name: Thomas R. Baruch
                                       Title: General Partner

              [Amended and Restated Stockholders Voting Agreement]
<PAGE>
                                       CMEA VENTURES LIFE SCIENCES 2000,
                                       CIVIL LAW PARTNERSHIP

                                       By: /s/ Thomas R. Baruch
                                           -------------------------------------
                                       Name: Thomas R. Baruch
                                       Title: General Partner

              [Amended and Restated Stockholders Voting Agreement]
<PAGE>
                                       P/S BI BIOMEDICINSK VENTURE III

                                       By:        /s/ Jesper Zeuthen
                                           -------------------------------------
                                       Name:          Jesper Zeuthen
                                             -----------------------------------
                                       Title: Managing Director

                                       CLARIDEN BANK

                                       By:        /s/ Eric Bernhardt
                                           -------------------------------------
                                       Name: Eric Bernhardt
                                       Title: Senior Vice President

              [Amended and Restated Stockholders Voting Agreement]
<PAGE>
                                    EXHIBIT A

                                   Purchasers

WARBURG PINCUS PRIVATE EQUITY VIII, L.P.
466 Lexington Avenue
New York, NY 10017
Attention: Stewart Hen

U.S. VENTURE PARTNERS VIII, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

USVP VIII AFFILIATES FUND, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

USVP ENTREPRENEUR PARTNERS VIII-A, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

USVP ENTREPRENEUR PARTNERS VIII-B, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

NOMURA PHASE4 VENTURES LP
c/o Nomura International plc
Nomura House
1 St. Martin's-le-Grand
London EC1A 4NP
United Kingdom
Attention: Charles Sermon

P/S BI BIOMEDICINSK VENTURE III
Sundkrogsgade 7
P.O. Box 2672
DK-2100 Copenhagen
Denmark
Attention: Jens W. Kindtler
<PAGE>
CLARIDEN BANK
Claridenstrasse 26
CH-8022 Zurich
Switzerland
Attention: Eric Bernhardt

CMEA VENTURES LIFE SCIENCES 2000, L.P.
One Embarcadero Center, Suite 3250
San Francisco, CA 94111
415.352.1520 ext. 200 (voice)
415.352.1524 (fax)
Attention: David Collier and Meryl Schreibstein

CMEA VENTURES LIFE SCIENCES 2000, CIVIL LAW PARTNERSHIP
One Embarcadero Center, Suite 3250
San Francisco, CA 94111
415.352.1520 ext. 200 (voice)
415.352.1524 (fax)
Attention: David Collier and Meryl Schreibstein

KIM FENNEBRESQUE
c/o SG Cowen & Co.
1221 Avenue of the Americas, 10th Floor
New York, NY 10020
(212) 278-4000 (office)
(212) 278-1641 (fax)

DAVID M. MALCOLM
460 Long Ridge
Bedford, NY 10530
(212) 278-4000 (office)
(212) 278-5599 (fax)

STELIOS PAPADOPOULOS
3 Summerset Drive South
Great Neck, NY 11020
(516) 487-5654 (home)
(516) 487-0245 (fax)

PETER REIKES
200 East 64th Street, #23A
New York, NY 10021
(212) 278-4000 (office)
(212) 278-4289 (fax)
<PAGE>
SENGAL M. SELASSIE
187 Gates Avenue
Montclair, NJ 01042
(973) 744-7525 (home)
(973) 744-7569 (fax)
(212) 278-4000 (office)
(212) 278-5454 (fax)

CHRISTOPHER A. WHITE
247 West 87th Street, #18F
New York, NY 10024
(212) 278-4000 (office)
(212) 278-5454 (fax)

NOMURA INTERNATIONAL PLC
Nomura House
1 St. Martin's-le-Grand
London EC1A 4NP
United Kingdom
Attention: Charles Sermon

SG COWEN VENTURES I, L.P.
1221 Avenue of the Americas
New York, NY 10020

PAUL J. LEACH
1134 Federal Avenue East
Seattle, WA 98102

ML INVESTMENTS LLC
One Financial Center
Boston, MA 02111

CHINA DEVELOPMENT INDUSTRIAL BANK INCORPORATED
125, Nanking East Road, Section 5
Taipei 105
Taiwan, R.O.C.
Attn: James Yen

PALLADIN OPPORTUNITY FUND LLC
195 Maplewood Avenue
Maplewood, NJ 07040
Attn: Ira Leiderman
<PAGE>
CDIB BIOTECH USA INVESTMENT, CO.
21 North Skokie Highway, Suite 104
Lake Bluff, IL 60044
Attn:Geoffrey Bonn

BAOTUNG VENTURE CAPITAL CORPORATION
10F, 261, Sung-Chiang Road
Taipei
Taiwan, R.O.C.
Attn: Joyce Lee, Ph. D.

WANTUNG VENTURE CAPITAL CORPORATION
10F, 261, Sung-Chiang Road
Taipei
Taiwan, R.O.C.
Attn: Joyce Lee, Ph. D.

CHUNG-SHAN VENTURE CAPITAL CORPORATION
10F, 261, Sung-Chiang Road
Taipei
Taiwan, R.O.C.
Attn: Joyce Lee, Ph. D.

CHUNG-SHAN II VENTURE CAPITAL CORPORATION
10F, 261, Sung-Chiang Road
Taipei
Taiwan, R.O.C.
Attn: Joyce Lee, Ph. D.
<PAGE>

                               FIRST AMENDMENT TO
               AMENDED AND RESTATED STOCKHOLDERS' VOTING AGREEMENT

         This Amendment to the AMENDED AND RESTATED STOCKHOLDERS' VOTING
AGREEMENT dated as of May 21, 2004 (the "Stockholders Agreement") is entered
into as of May 9, 2005, by and among Altus Pharmaceuticals Inc., a Delaware
corporation (the "Company"), and the persons and entitites listed on Exhibit A
hereto (each referred to in this Amendment as a "Stockholder" as defined in the
Stockholders Agreement, and collectively referred to herein as "Stockholders").

                                  WITNESSETH

         WHEREAS, the Company and the Stockholders entered into the Stockholders
Agreement in order to provide for continuity of the Board of Directors of the
Company; and

         WHEREAS, in order to accommodate certain management changes, the
Company and the Stockholders wish to amend the Stockholders Agreement as set
forth below; and

         WHEREAS, the undersigned parties represent the necessary voting power
required to amend the Stockholders Agreement as set forth in Section 7(f)
thereof.

         NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Amendment, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, agree as follows:

         1. Amendment to subsection (a) of Section 1 of the Stockholders
Agreement. The Stockholders Agreement shall be amended by deleting subsection
(a) of Section 1 and replacing such sentence in its entirety with the following:

         "In any and all elections of directors of the Company (whether at a
         meeting or by written consent in lieu of a meeting), each Stockholder
         shall vote or cause to be voted all Shares (as defined in Section 2
         below) owned by him, her or it, or over which he, she or it has voting
         control, and otherwise use his, her or its respective best efforts, so
         as to fix the number of directors of the Company at ten (10) and to
         elect to the Board as directors (i) one (1) member designated by
         Nomura, (ii) one (1) member designated by USVP, (iii) one (1) member
         designated by Vertex, (iv) two (2) members designated by the holders of
         a majority of the outstanding shares of Series C Preferred Stock, (v)
         the Company's Chief Executive Officer and (vi) four (4) members, who
         shall not be employed by the Company, designated by not less than three
         (3) of the Series B Directors and Series C Directors
<PAGE>
         (as defined below) (the "Outside Directors"). The directors designated
         by the holders of a majority of the outstanding shares of Series C
         Preferred Stock shall be the Series C Directors (as defined in the
         Company's Third Amended and Restated Certificate of Incorporation, as
         amended (the "Charter")), the directors designated by Nomura and USVP
         shall be the Series B Directors (as defined in the Charter) and the
         director designated by Vertex shall be the Series A Director (as
         defined in the Charter). As of the date hereof, the directors
         designated by the holders of a majority of the outstanding shares of
         Series C Preferred Stock shall be Stewart Hen and Jonathan Leff, the
         director designated by Nomura shall be John Richard, the director
         designated by USVP shall be Jonathan Root, the director designated by
         Vertex shall be Lynne Brum, and the four (4) Outside Directors shall be
         Manuel Navia, Richard Aldrich, Michael Wyzga and Peter Lanciano."

         2. Prior Agreements. By execution of this Amendment, the parties
hereto, holding in the aggregate a sufficient number of shares of stock to amend
the Stockholders Agreement in accordance with Section 7(f) thereof, hereby
agree, for and on behalf of all parties to the Stockholders Agreement, that the
aforementioned section be amended. Any signatory to the Stockholders Agreement
who does not sign this Amendment shall be bound by the terms and conditions of
this Amendment, pursuant to the provisions of Section 7(f) of the Stockholders
Agreement, as if the signatory to the Stockholders Agreement had signed this
Amendment. All other provisions of the Stockholders Agreement not amended hereby
shall remain unchanged and continue in full force and effect.

         3. Counterparts. This Amendment may be executed by the parties in
separate counterparts, each of which when so executed and delivered will be an
original, but all of which together will constitute one and the same agreement.
In pleading or proving this Amendment, it will not be necessary to produce or
account for more than one such counterpart.

         4. Captions. The captions of sections or subsections of this Amendment
are for reference only and will not affect the interpretation or construction of
this Amendment.

         5. Severability. In the event that any one or more of the provisions
contained in this Amendment or in any other instrument referred to herein shall,
for any reason, be held to be invalid, illegal or unenforceable, such
illegality, invalidity or unenforceability shall not affect any other provisions
of this Agreement.

         6. Governing Law. This Amendment shall be governed by, and construed in
accordance with, the laws of the State of Delaware.

              [The rest of this page is intentionally left blank.]
<PAGE>
         IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the date set forth above.

COMPANY:                        ALTUS PHARMACEUTICALS INC.

                                By
                                     ---------------------------------------
                                     Name:
                                     Its:

STOCKHOLDERS:                   CMEA VENTURES LIFE SCIENCES 2000, L.P

                                By:      /s/ David Collier
                                         -----------------------------------
                                Name: David Collier
                                      --------------------------------------
                                Title:   General Partner
                                         -----------------------------------

                                CMEA VENTURES LIFE SCIENCES 2000,
                                CIVIL LAW PARTNERSHIP

                                By:      /s/ David Collier
                                         -----------------------------------
                                Name: David Collier
                                      --------------------------------------
                                Title:   General Partner
                                          ----------------------------------

                                NOMURA INTERNATIONAL PLC

                                By:      /s/ Denise Pollard-Knight
                                         -----------------------------------
                                Name: Denise Pollard-Knight
                                      --------------------------------------
                                Title:   Head of Phase4 Ventures
                                         -----------------------------------

                                NOMURA PHASE4 VENTURES LP

                                By:      /s/ Denise Pollard-Knight
                                         -----------------------------------
                                Name: Denise Pollard-Knight
                                      --------------------------------------
                                Title:   Head of Phase4 Ventures
                                         -----------------------------------

              Signature Page to Amendment to Stockholders Agreement
<PAGE>
                                U.S. VENTURE PARTNERS VIII, L.P.
                                USVP VIII AFFILIATES FUND, L.P.
                                USVP ENTREPRENEUR PARTNERS VIII-A, L.P.
                                USVP ENTREPRENEUR PARTNERS VIII-B, L.P.

                                By Presidio Management Group VIII, L.L.C.
                                The General Partner of Each

                                By:      /s/ Michael P. Maher
                                         -----------------------------------
                                Name: Michael P. Maher
                                      --------------------------------------
                                Title:   Attorney In-Fact
                                         -----------------------------------

                                WARBURG PINCUS PRIVATE EQUITY
                                VIII, L.P.

                                By:  WARBURG PINCUS & CO.
                                Its: General Partner

                                By:  /s/ Stewrt J. Hen
                                     ---------------------------------------
                                Name: Stewart J. Hen
                                      --------------------------------------
                                Title:   Partner
                                         -----------------------------------

              Signature Page to Amendment to Stockholders Agreement
<PAGE>
                                    EXHIBIT A

                                  Stockholders

CMEA Ventures Life Sciences 2000, L.P.
One Embarcadero Center, Suite 3250
San Francisco, CA 94111
415.352.1520 ext. 200 (voice)
415.352.1524 (fax)
Attention: David Collier and Meryl Schreibstein

CMEA Ventures Life Sciences 2000, Civil Law Partnership
One Embarcadero Center, Suite 3250
San Francisco, CA 94111
415.352.1520 ext. 200 (voice)
415.352.1524 (fax)
Attention: David Collier and Meryl Schreibstein

Nomura International plc
Nomura House
1 St. Martin's-le-Grand
London EC1A 4NP
United Kingdom
Attention:

Nomura Phase4 Ventures LP
c/o Nomura International plc
Nomura House
1 St. Martin's-le-Grand
London EC1A 4NP
United Kingdom
Attention:

U.S. Venture Partners VIII, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

USVP VIII Affiliates Fund, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher
<PAGE>
USVP Entrepreneur Partners VIII-A, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

USVP Entrepreneur Partners VIII-B, L.P.
2735 Sand Hill Road
Menlo Park, CA 94025
Attention: Michael Maher

Warburg Pincus Private Equity VIII, L.P.
466 Lexington Avenue
New York, NY 10017
Attention: Stewart Hen<PAGE>

                                                                    EXHIBIT 10.7

                            INDEMNIFICATION AGREEMENT

         THIS AGREEMENT is made and entered into this ___ day of
_______________, 20__ by and between ALTUS PHARMACEUTICALS INC., a Delaware
corporation (the "Corporation"), and _______________ ("Agent").

                                    RECITALS

         WHEREAS, Agent performs a valuable service to the Corporation in his
capacity as [a director/an officer] of the Corporation;

         WHEREAS, the Corporation has adopted provisions in its Certificate of
Incorporation (the "Charter") and bylaws (the "Bylaws") providing for the
indemnification of the directors, officers, employees and other agents of the
Corporation, including persons serving at the request of the Corporation in such
capacities with other corporations or enterprises, as authorized by the Delaware
General Corporation Law, as amended (the "Code");

         WHEREAS, the Charter, the Bylaws and the Code, by their non-exclusive
nature, permit contracts between the Corporation and its agents, officers,
employees and other agents with respect to indemnification of such persons; and

         WHEREAS, in order to induce Agent to serve as [a director/an officer]
of the Corporation, the Corporation has determined and agreed to enter into this
Agreement with Agent.

         NOW, THEREFORE, in consideration of Agent's service as [a director/an
officer] of the Corporation after the date hereof, the parties hereto agree as
follows:

                                    AGREEMENT

         1. Services to the Corporation. Agent will serve, at the will of the
Corporation or under separate contract, if any such contract exists, as [a
director/an officer] of the Corporation or as a director, officer or other
fiduciary of an affiliate of the Corporation (including any employee benefit
plan of the Corporation) faithfully and to the best of his ability so long as he
[is duly elected and qualified in accordance with the provisions of the Bylaws
or other applicable charter documents/is a duly appointed officer] of the
Corporation or such affiliate; provided, however, that Agent may at any time and
for any reason resign from such position (subject to any contractual obligation
that Agent may have assumed apart from this Agreement) and that the Corporation
or any affiliate shall have no obligation under this Agreement to continue Agent
in any such position.

         2. Indemnity of Agent. The Corporation hereby agrees to hold harmless
and indemnify Agent to the fullest extent authorized or permitted by the
provisions of the Charter, the Bylaws and the Code, as the same may be amended
from time to time (but, only to the extent
<PAGE>
that such amendment permits the Corporation to provide broader indemnification
rights than the Charter, the Bylaws or the Code permitted prior to adoption of
such amendment).

         3. Additional Indemnity. In addition to and not in limitation of the
indemnification otherwise provided for herein, and subject only to the
exclusions set forth in Section 4 hereof, the Corporation hereby further agrees
to hold harmless and indemnify Agent:

                  (a) against any and all expenses (including attorneys' fees),
witness fees, damages, judgments, fines and amounts paid in settlement and any
other amounts that Agent becomes legally obligated to pay because of any claim
or claims made against or by him in connection with any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, arbitrational,
administrative or investigative (including an action by or in the right of the
Corporation) to which Agent is, was or at any time becomes a party or a witness,
or is threatened to be made a party or a witness, by reason of the fact that
Agent is, was or at any time becomes a director, officer, employee or other
agent of Corporation, or is or was serving or at any time serves at the request
of the Corporation as a director, officer, employee or other agent of another
corporation, partnership, joint venture, trust, employee benefit plan or other
enterprise; and

                  (b) otherwise to the fullest extent as may be provided to
Agent by the Corporation under the non-exclusivity provisions of the Code, the
Charter and the Bylaws.

         4. Limitations on Additional Indemnity. No indemnity pursuant to
Section 3 hereof shall be paid by the Corporation:

                  (a) on account of any claim against Agent for an accounting of
profits made from the purchase or sale by Agent of securities of the Corporation
pursuant to the provisions of Section 16(b) of the Securities Exchange Act of
1934 and amendments thereto or similar provisions of any federal, state or local
statutory law;

                  (b) on account of Agent's conduct that is established by a
final judgment as knowingly fraudulent or deliberately dishonest or that
constituted willful misconduct;

                  (c) on account of Agent's conduct that is established by a
final judgment as constituting a breach of Agent's duty of loyalty to the
Corporation or resulting in any personal profit or advantage to which Agent was
not legally entitled;

                  (d) for which payment is actually made to Agent under a valid
and collectible insurance policy or under a valid and enforceable indemnity
clause, bylaw or agreement, except in respect of any excess beyond payment under
such insurance, clause, bylaw or agreement;

                  (e) if indemnification is not lawful (and, in this respect,
both the Corporation and Agent have been advised that the Securities and
Exchange Commission believes that indemnification for liabilities arising under
the federal securities laws is against public policy and is, therefore,
unenforceable and that claims for indemnification should be submitted to
appropriate courts for adjudication); or

                                       2
<PAGE>
                  (f) in connection with any proceeding (or part thereof)
initiated by Agent, or any proceeding by Agent against the Corporation or its
directors, officers, employees or other agents, unless (i) such indemnification
is expressly required to be made by law, (ii) the proceeding was authorized by
the Board of Directors of the Corporation, (iii) such indemnification is
provided by the Corporation, in its sole discretion, pursuant to the powers
vested in the Corporation under the Code, or (iv) the proceeding is initiated
pursuant to Section 9 hereof.

         5. Continuation of Indemnity. All agreements and obligations of the
Corporation contained herein shall continue during the period Agent is a
director, officer, employee or other agent of the Corporation (or is or was
serving at the request of the Corporation as a director, officer, employee or
other agent of another corporation, partnership, joint venture, trust, employee
benefit plan or other enterprise) and shall continue thereafter so long as Agent
shall be subject to any possible claim or threatened, pending or completed
action, suit or proceeding, whether civil, criminal, arbitrational,
administrative or investigative, by reason of the fact that Agent was serving in
the capacity referred to herein.

         6. Partial Indemnification. Agent shall be entitled under this
Agreement to indemnification by the Corporation for a portion of the expenses
(including attorneys' fees), witness fees, damages, judgments, fines and amounts
paid in settlement and any other amounts that Agent becomes legally obligated to
pay in connection with any action, suit or proceeding referred to in Section 3
hereof even if not entitled hereunder to indemnification for the total amount
thereof, and the Corporation shall indemnify Agent for the portion thereof to
which Agent is entitled.

         7. Notification and Defense of Claim. Not later than thirty (30) days
after Agent becomes aware, by written or other overt communication, of any
pending or threatened litigation, claim or assessment, Agent will, if a claim in
respect thereof is to be made against the Corporation under this Agreement,
notify the Corporation of such pending or threatened litigation, claim or
assessment; but the omission so to notify the Corporation will not relieve it
from any liability which it may have to Agent otherwise than under this
Agreement. With respect to any such pending or threatened litigation, claim or
assessment as to which Agent notifies the Corporation of the commencement
thereof:

                  (a) the Corporation will be entitled to participate therein at
its own expense;

                  (b) except as otherwise provided below, the Corporation may,
at its option and jointly with any other indemnifying party similarly notified
and electing to assume such defense, assume the defense thereof, with counsel
reasonably satisfactory to Agent. After notice from the Corporation to Agent of
its election to assume the defense thereof, the Corporation will not be liable
to Agent under this Agreement for any legal or other expenses subsequently
incurred by Agent in connection with the defense thereof except for reasonable
costs of investigation or otherwise as provided below. Agent shall have the
right to employ separate counsel in such action, suit or proceeding but the fees
and expenses of such counsel incurred after notice from the Corporation of its
assumption of the defense thereof shall be at the expense of Agent unless (i)
the employment of counsel by Agent has been authorized by the Corporation, (ii)
Agent shall have reasonably concluded, and so notified the Corporation, that
there is an

                                       3
<PAGE>
actual conflict of interest between the Corporation and Agent in the conduct of
the defense of such action or (iii) the Corporation shall not in fact have
employed counsel to assume the defense of such action, in each of which cases
the fees and expenses of Agent's separate counsel shall be at the expense of the
Corporation. The Corporation shall not be entitled to assume the defense of any
action, suit or proceeding brought by or on behalf of the Corporation or as to
which Agent shall have made the conclusion provided for in clause (ii) above;
and

                  (c) the Corporation shall not be liable to indemnify Agent
under this Agreement for any amounts paid in settlement of any action or claim
effected without its written consent, which shall not be unreasonably withheld.
The Corporation shall be permitted to settle any action or claim except that it
shall not settle any action or claim in any manner which would impose any
penalty or limitation on Agent without Agent's written consent, which may be
given or withheld in Agent's sole discretion.

         8. Expenses. The Corporation shall advance, prior to the final
disposition of any proceeding, promptly following request therefor, all expenses
incurred by Agent in connection with such proceeding upon receipt of an
undertaking by or on behalf of Agent to repay said amounts if it shall be
determined ultimately that Agent is not entitled to be indemnified under the
provisions of this Agreement, the Charter, the Bylaws, the Code or otherwise.

         9. Enforcement. Any right to indemnification or advances granted by
this Agreement to Agent shall be enforceable by or on behalf of Agent in any
court of competent jurisdiction if (i) the claim for indemnification or advances
is denied, in whole or in part, or (ii) no disposition of such claim is made
within ninety (90) days of request therefor. Agent, in such enforcement action,
if successful in whole or in part, shall be entitled to be paid also the expense
of prosecuting his claim. It shall be a defense to any action for which a claim
for indemnification is made under Section 3 hereof (other than an action brought
to enforce a claim for expenses pursuant to Section 8 hereof, provided that the
required undertaking has been tendered to the Corporation) that Agent is not
entitled to indemnification because of the limitations set forth in Section 4
hereof. Neither the failure of the Corporation (including its Board of Directors
or its stockholders) to have made a determination prior to the commencement of
such enforcement action that indemnification of Agent is proper in the
circumstances, nor an actual determination by the Corporation (including its
Board of Directors or its stockholders) that such indemnification is improper
shall be a defense to the action or create a presumption that Agent is not
entitled to indemnification under this Agreement or otherwise.

         10. Subrogation. In the event of payment under this Agreement, the
Corporation shall be subrogated to the extent of such payment to all of the
rights of recovery of Agent, who shall execute all documents required and shall
do all acts that may be necessary to secure such rights and to enable the
Corporation effectively to bring suit to enforce such rights.

         11. Non-Exclusivity of Rights. The rights conferred on Agent by this
Agreement shall not be exclusive of any other right which Agent may have or
hereafter acquire under any statute, provision of the Corporation's Certificate
of Incorporation or Bylaws, agreement, vote of stockholders or directors, or
otherwise, both as to action in his official capacity and as to action in
another capacity while holding office.

                                       4
<PAGE>
         12. Survival of Rights.

                  (a) The rights conferred on Agent by this Agreement shall
continue after Agent has ceased to be a director, officer, employee or other
agent of the Corporation or to serve at the request of the Corporation as a
director, officer, employee or other agent of another corporation, partnership,
joint venture, trust, employee benefit plan or other enterprise, and shall inure
to the benefit of Agent's heirs, executors and administrators.

                  (b) The Corporation shall require any successor (whether
direct or indirect, by purchase, merger, consolidation or otherwise) to all or
substantially all of the business or assets of the Corporation, expressly to
assume and agree to perform this Agreement in the same manner and to the same
extent that the Corporation would be required to perform if no such succession
had taken place.

         13. Separability. Each of the provisions of this Agreement is a
separate and distinct agreement and independent of the others, so that if any
provision hereof shall be held to be invalid or unenforceable for any reason,
such invalidity or unenforceability shall not affect the validity or
enforceability of the other provisions hereof. Furthermore, if this Agreement
shall be invalidated in its entirety on any ground, then the Corporation shall
nevertheless indemnify Agent to the fullest extent provided by the Charter, the
Bylaws, the Code or any other applicable law.

         14. Governing Law. This Agreement shall be interpreted and enforced in
accordance with the laws of the State of Delaware.

         15. Amendment and Termination. No amendment, modification, termination
or cancellation of this Agreement shall be effective unless in writing signed by
both parties hereto.

         16. Identical Counterparts. This Agreement may be executed in one or
more counterparts, each of which shall for all purposes be deemed to be an
original but all of which together shall constitute but one and the same
Agreement. Only one such counterpart need be produced to evidence the existence
of this Agreement.

         17. Headings. The headings of the sections of this Agreement are
inserted for convenience only and shall not be deemed to constitute part of this
Agreement or to affect the construction hereof.

         18. Notices. All notices, requests, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given (i)
upon delivery if delivered by hand to the party to whom such communication was
directed or (ii) upon the third business day after the date on which such
communication was mailed if mailed by certified or registered mail with postage
prepaid:

                  (a) If to Agent, at the address indicated on the signature
page hereof.

                  (b) If to the Corporation, to:

                           Altus Pharmaceuticals Inc.

                                       5
<PAGE>
                           125 Sidney Street
                           Cambridge, MA 02139
                           Attention: Chief Executive Officer

         or to such other address as may have been furnished to Agent by the
Corporation.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement on
and as of the day and year first above written.

                                           ALTUS PHARMACEUTICALS INC.

                                           By:________________________________
                                           Name:
                                           Title:

                                           AGENT

                                           ___________________________________
                                            [Name]

                                           Address:
                                           ___________________________________
                                           ___________________________________

                                       6

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