# EDGAR Filing Document

**Accession Number:** 0002127815
**File Stem:** 0000905148-26-002932
**Filing Date:** 2026-6
**Character Count:** 12158
**Document Hash:** 1d3c3b2bd02340b0a74834eabf0d67e5
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000905148-26-002932.hdr.sgml**: 20260612

**ACCESSION NUMBER**: 0000905148-26-002932

**CONFORMED SUBMISSION TYPE**: 3

**PUBLIC DOCUMENT COUNT**: 2

**CONFORMED PERIOD OF REPORT**: 20260608

**FILED AS OF DATE**: 20260612

**DATE AS OF CHANGE**: 20260612

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Isaacs Michael John
- **CENTRAL INDEX KEY:** 0002127815

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 3
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-35676
- **FILM NUMBER:** 261086982

**MAIL ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY
- **STREET 2:** C/O PROTHENA BIOSCIENCES INC
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** PROTHENA CORP PUBLIC LTD CO
- **CENTRAL INDEX KEY:** 0001559053
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** L2
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 77 SIR JOHN ROGERSON'S QUAY, BLOCK C
- **STREET 2:** GRAND CANAL DOCKLANDS
- **CITY:** DUBLIN 2
- **STATE:** L2
- **ZIP:** D02 VK60
- **BUSINESS PHONE:** 011-353-1-236-2500

**MAIL ADDRESS:**
- **STREET 1:** 77 SIR JOHN ROGERSON'S QUAY, BLOCK C
- **STREET 2:** GRAND CANAL DOCKLANDS
- **CITY:** DUBLIN 2
- **STATE:** L2
- **ZIP:** D02 VK60

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Prothena Corp plc
- **DATE OF NAME CHANGE:** 20121102

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Neotope Corp Ltd
- **DATE OF NAME CHANGE:** 20120926

## Ex-24

**POWER OF ATTORNEY**

**KNOW ALL BY THESE PRESENTS**, that the undersigned hereby constitutes and appoints Michael J. Malecek, Karin L. Walker and Kevin J. Hickey, and their respective successors, and each of them the undersigned's true and lawful attorneys-in-fact and agents with full power of substitution, signing singly, for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to:

&nbsp;&nbsp;&nbsp;&nbsp;

1. prepare, execute in the undersigned's name and on the undersigned's behalf, and submit to the U.S. Securities and Exchange Commission (the "SEC") a Form ID, including amendments thereto, and any other documents necessary or appropriate to obtain codes and passwords enabling the undersigned to make electronic filings with the SEC of reports required by Section 16(a) of the Securities Exchange Act of 1934 (as amended, the "Exchange Act") or any rule or regulation of the SEC;

&nbsp;&nbsp;&nbsp;&nbsp;

2. complete, execute and timely file for and on behalf of the undersigned, in the undersigned's capacity as an officer and/or director of Prothena Corporation plc (the "Company"), Forms 3, 4 and 5, any other forms, and any amendments thereto in accordance with Section 16(a) of the Exchange Act and the rules and regulations thereunder; and

&nbsp;&nbsp;&nbsp;&nbsp;

3. take any other action of any type whatsoever in connection with the foregoing which, in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by, the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-fact's discretion.

The undersigned hereby grants to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact's substitute or substitutes, shall lawfully do or cause to be done by virtue of this power of attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming, nor is the Company assuming, any of the undersigned's responsibilities to comply with Section 16 of the Exchange Act.

The undersigned agrees that each such attorney-in-fact herein may rely entirely on information furnished orally or in writing by the undersigned to such attorney-in-fact. The undersigned also agrees to indemnify and hold harmless the Company and each such attorney-in-fact against any losses, claims, damages or liabilities (or actions in these respects) that arise out of or are based upon any untrue statements or omission of necessary facts in the information provided by the undersigned to such attorney-in fact for purposes of executing, acknowledging, delivering or filing Forms 3, 4 or 5, Form ID or any other form (including amendments thereto) and agrees to reimburse the Company and such attorney-in-fact for any legal or other expenses reasonably incurred in connection with investigating or defending against any such loss, claim, damage, liability or action.

This Power of Attorney supersedes any power of attorney previously executed by the undersigned regarding the purposes outlined in the first paragraph hereof ("Prior Powers of Attorney"), and the authority of the attorneys-in-fact named in any Prior Powers of Attorney is hereby revoked.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5 with respect to the undersigned's holdings of and transactions in securities issued by the Company, unless earlier (a) revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact or (b) superseded by a new power of attorney regarding the purposes outlined in the first paragraph hereof dated as of a later date.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 3rd day of April, 2026.

Signature:

/s/ Michael John Isaacs

Name:

Michael John Isaacs

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 3

### INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>Isaacs Michael John<br><sub>(Last) (First) (Middle)</sub><br>C/O PROTHENA BIOSCIENCES INC.<br>1800 SIERRA POINT PARKWAY<br><sub>(Street)</sub><br>BRISBANE, CA 94005<br><sub>(City) (State) (Zip)</sub> | **3. Issuer Name and Ticker or Trading Symbol**<br>PROTHENA CORP PUBLIC LTD CO [ PRTA ] | **5. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  |
| **2. Date of Event Requiring Statement (Month/Day/Year)**<br>2026-06-08 | **4. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[ ] Director   [ ] 10% Owner<br>[X] Officer (give title below)   [ ] Other (specify below)<br>_General Counsel & Company Sec._ | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities Beneficially Owned

---

|  |  |  |  |
| --- | --- | --- | --- |
| 1. Title of Security | 2. Amount of Securities Beneficially Owned | 3. Ownership Form | 4. Nature of Indirect Beneficial Ownership |
| Ordinary Shares, par value $0.01 per share | 48825 | D |  |

---

## Table II - Derivative Securities Beneficially Owned

---

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 3. Title and Amount of Underlying Securities | 3. Title and Amount of Underlying Securities | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| Stock Option (Right to Buy) | <sup>(1)</sup> | 2030-04-01 | Ordinary Shares | 17500 | $10.99 | D |  |
| Stock Option (Right to Buy) | <sup>(1)</sup> | 2031-02-25 | Ordinary Shares | 10000 | $22.60 | D |  |
| Stock Option (Right to Buy) | <sup>(1)</sup> | 2032-02-23 | Ordinary Shares | 8250 | $32.45 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2033-03-02 | Ordinary Shares | 8800 | $52.97 | D |  |
| Stock Option (Right to Buy) | <sup>(3)</sup> | 2034-02-27 | Ordinary Shares | 12000 | $30.30 | D |  |
| Stock Option (Right to Buy) | <sup>(4)</sup> | 2035-03-05 | Ordinary Shares | 8612 | $14.95 | D |  |
| Stock Option (Right to Buy) | <sup>(5)</sup> | 2036-03-03 | Ordinary Shares | 37500 | $9.36 | D |  |
| Stock Option (Right to Buy) | <sup>(6)</sup> | 2036-04-10 | Ordinary Shares | 50000 | $10.50 | D |  |

---

### Footnotes:

(1) The option is fully vested.

(2) The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 2, 2024, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.

(3) The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on February 27, 2025, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.

(4) The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 5, 2026, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.

(5) The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on March 3, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.

(6) The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on April 10, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.

**Remarks:**
Exhibit List: Exhibit 24 - Power of Attorney

**Signature:** /s/ Michael J. Isaacs  
**Date:** 2026-06-12

### Remarks:

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

**Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.**