FMR LLC reports 13.8% stake in Prothena

FMR LLC reported beneficial ownership of common stock of Prothena Corporation plc.

Rhea-AI Filing Summary

FMR LLC reported beneficial ownership of common stock of Prothena Corporation plc. FMR LLC held 7,199,218 shares, representing 13.8% of the outstanding common stock as of June 30, 2026, with sole power to dispose of all such shares and no shared voting or dispositive power.

Abigail P. Johnson is reported with sole dispositive power over the same 7,199,218 shares, but no sole or shared voting power. The filing notes that one or more other persons have rights to receive dividends or sale proceeds, including Fidelity Growth Company Commingled Pool, whose interest amounted to 3,335,877 shares, or 6.4% of Prothena’s common stock as of June 30, 2026.

Key Figures

Beneficial ownership: 7,199,218 shares Percent of class: 13.8% Sole dispositive power (FMR LLC): 7,199,218 shares +4 more

7 metrics

Beneficial ownership 7,199,218 shares Shares of Prothena common stock beneficially owned by FMR LLC

Percent of class 13.8% Percentage of Prothena common stock class beneficially owned by FMR LLC

Sole dispositive power (FMR LLC) 7,199,218 shares Shares over which FMR LLC has sole power to dispose

Sole dispositive power (Abigail P. Johnson) 7,199,218 shares Shares over which Abigail P. Johnson has sole dispositive power

Fidelity Growth Company Commingled Pool holding 3,335,877 shares Interest in Prothena common stock held through the commingled pool

Commingled Pool percent of class 6.4% Percentage of total outstanding Prothena common stock at 06/30/2026

As-of date 06/30/2026 Date for ownership and percentage calculations in the filing

Key Terms

beneficially owned, sole dispositive power, shared voting power, Schedule 13G, +1 more

5 terms

beneficially owned financial

"Item 4. | Ownership (a) | Amount beneficially owned: 7199218.00"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole dispositive power financial

"Sole Dispositive Power 7,199,218.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

shared voting power financial

"Shared Voting Power 0.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

Schedule 13G regulatory

"Please see Exhibit 99 for 13d-1(k) (1) agreement."

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

commingled pool financial

"The interest of Fidelity Growth Company Commingled Pool, in the COMMON STOCK"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many Prothena (PRTA) shares does FMR LLC report owning?

FMR LLC reports beneficial ownership of 7,199,218 shares of Prothena common stock, representing 13.8% of the class as of June 30, 2026, with sole dispositive power over all such shares.

What percentage of Prothena (PRTA) does FMR LLC control?

FMR LLC reports holding 13.8% of Prothena’s common stock, based on 7,199,218 shares beneficially owned. This position gives FMR LLC sole dispositive power but no shared voting or dispositive authority.

What interest does Fidelity Growth Company Commingled Pool hold in Prothena (PRTA)?

Fidelity Growth Company Commingled Pool’s interest amounted to 3,335,877 shares of Prothena common stock, or 6.4% of total outstanding shares as of June 30, 2026, with rights to dividends or sale proceeds on those shares.

What is Abigail P. Johnson’s reported role in Prothena (PRTA) share ownership?

Abigail P. Johnson is reported with sole dispositive power over 7,199,218 shares of Prothena common stock, matching FMR LLC’s beneficial ownership, but with no sole or shared voting power reported for those shares.

Does any other party have rights to Prothena (PRTA) dividends or sale proceeds?

Yes. One or more other persons have rights to receive dividends or sale proceeds, including Fidelity Growth Company Commingled Pool, whose 3,335,877-share interest equals 6.4% of Prothena’s outstanding common stock as of June 30, 2026.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 08/06/2026 - 10:40 AM Accepted by SEC EDGAR 08/06/2026 - 10:38 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 4)

PROTHENA CORP PLC

(Name of Issuer)

COMMON STOCK

(Title of Class of Securities)

G72800108

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): G72800108

1

Names of Reporting Persons

FMR LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 7,199,218.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 7,199,218.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

7,199,218.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

13.8 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

CUSIP Number(s): G72800108

1

Names of Reporting Persons

Abigail P. Johnson

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 7,199,218.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

7,199,218.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

13.8 %

12

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: PROTHENA CORP PLC
(b)	Address of issuer's principal executive offices: 77 SIR JOHN ROGERSON'S QUAY,BLOCK C, GRAND CANAL DOCKLANDS,DUBLIN 2,L2,D02 VK60
Item 2.
(a)	Name of person filing: FMR LLC
(b)	Address or principal business office or, if none, residence: 245 Summer Street, Boston, Massachusetts 02210
(c)	Citizenship: Not applicable
(d)	Title of class of securities: COMMON STOCK
(e)	CUSIP No.: G72800108
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 7199218.00
(b)	Percent of class: 13.8 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Please see the responses to Items 5 and 6 on the cover page.
	(ii) Shared power to vote or to direct the vote: 0.00
	(iii) Sole power to dispose or to direct the disposition of: 7199218.00
	(iv) Shared power to dispose or to direct the disposition of: 0.00
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. One or more other persons are known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the COMMON STOCK of PROTHENA CORP PLC. The interest of Fidelity Growth Company Commingled Pool, in the COMMON STOCK of PROTHENA CORP PLC, amounted to 3335877.00 shares or 6.4% of the total outstanding COMMON STOCK at 06/30/2026.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. See attached Exhibit 99.
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

FMR LLC

Signature:	Stephanie J. Brown
Name/Title:	Duly authorized under Power of Attorney effective as of January 3, 2023, by and on behalf of FMR LLC and its direct and indirect subsidiaries*
Date:	08/05/2026

Abigail P. Johnson

Signature:	Stephanie J. Brown
Name/Title:	Duly authorized under Power of Attorney effective as of January 26, 2023, by and on behalf of Abigail P. Johnson**
Date:	08/05/2026

Comments accompanying signature: * This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 10, 2023, accession number: 0000315066-23-000003. ** This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 31, 2023, accession number: 0000315066-23-000038.

Exhibit Information

Please see Exhibit 99 for 13d-1(k) (1) agreement.