Rubric Capital (PRTA) discloses 6.83% Prothena stake via 3.68M shares

Rhea-AI Filing Summary

Rubric Capital Management LP and David Rosen disclosed beneficial ownership of Prothena Corporation plc’s ordinary shares. They report holding 3,677,331 ordinary shares, representing 6.83% of the outstanding class.

The percentage is calculated based on 53,829,982 ordinary shares outstanding as of October 31, 2025, as reported by Prothena. Rubric Capital Master Fund LP has the right to receive dividends or sale proceeds on more than 5% of the shares. The investors state that the shares are held in the ordinary course of business and not for the purpose of changing or influencing control of Prothena.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

PROTHENA CORPORATION PUBLIC LIMITED COMPANY

(Name of Issuer)

Ordinary Shares, par value $0.01 per share

(Title of Class of Securities)

G72800108

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. G72800108

1

Names of Reporting Persons

Rubric Capital Management LP

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 0.00
6	Shared Voting Power 3,677,331.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 3,677,331.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,677,331.00

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)

6.83 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP No. G72800108

1

Names of Reporting Persons

David Rosen

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 3,677,331.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 3,677,331.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,677,331.00

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)

6.83 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: PROTHENA CORPORATION PUBLIC LIMITED COMPANY
(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: This statement is filed by: (i) Rubric Capital Management LP ("Rubric Capital"), the investment adviser to certain investment funds and/or accounts (collectively, the "Rubric Funds") that hold the Ordinary Shares, par value $0.01 per share (the "Ordinary Shares") of Prothena Corporation plc, an Irish public limited company (the "Issuer") reported herein; and (ii) David Rosen ("Mr. Rosen"), Managing Member of Rubric Capital Management GP LLC, the general partner of Rubric Capital. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." The filing of this statement should not be construed as an admission that any of the forgoing persons or any Reporting Person is, for the purposes of Section 13 of the Act, the beneficial owner of the Shares reported herein.
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is 155 East 44th St, Suite 1630, New York, NY 10017.
(c)	Citizenship: Rubric Capital is a Delaware limited partnership. Mr. Rosen is a citizen of the United States of America.
(d)	Title of class of securities: Ordinary Shares, par value $0.01 per share
(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: The information required by Items 4(a) - (c) is set forth in Rows 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentage set forth in Row (11) of the cover page for each of the Reporting Persons and in Item 4(b) is based on the 53,829,982 Ordinary Shares outstanding as of October 31, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2025 filed with the Securities and Exchange Commission on November 6, 2025.
(b)	Percent of class: 6.83 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(ii) Shared power to vote or to direct the vote: The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iii) Sole power to dispose or to direct the disposition of: The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iv) Shared power to dispose or to direct the disposition of: The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
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. See Item 2(a). Rubric Capital Master Fund LP, a Rubric Fund, has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, more than 5% of the Ordinary Shares.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
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.

Rubric Capital Management LP

Signature:	/s/ Michael Nachmani
Name/Title:	Michael Nachmani / Chief Operating Officer
Date:	02/13/2026

David Rosen

Signature:	/s/ David Rosen
Name/Title:	David Rosen / Individually
Date:	02/13/2026

Exhibit Information

Exhibit 99.1: Joint Filing Agreement

FAQ

What stake in Prothena (PRTA) did Rubric Capital report?

Rubric Capital reported beneficial ownership of 3,677,331 Prothena ordinary shares, representing 6.83% of the class. This percentage is based on 53,829,982 shares outstanding as of October 31, 2025, as disclosed in Prothena’s quarterly report.

Who are the reporting persons in this Prothena (PRTA) Schedule 13G?

The reporting persons are Rubric Capital Management LP and David Rosen. Rubric Capital acts as investment adviser to certain funds holding Prothena shares, and Rosen is the Managing Member of Rubric Capital’s general partner, giving them shared voting and dispositive power over the reported shares.

How much of Prothena’s (PRTA) stock can Rubric Capital vote or dispose of?

Rubric Capital and David Rosen report 0 shares with sole voting or dispositive power and 3,677,331 shares with shared voting and dispositive power. This means decisions over these shares are made jointly, not by either reporting person alone.

What is the ownership percentage basis used in this Prothena (PRTA) disclosure?

The stated 6.83% ownership is calculated using 53,829,982 Prothena ordinary shares outstanding as of October 31, 2025. That outstanding share figure comes from Prothena’s Form 10-Q for the quarter ended September 30, 2025.

Is Rubric Capital seeking control of Prothena (PRTA) with this stake?

The investors state the securities were acquired and are held in the ordinary course of business. They certify the shares were not acquired, and are not held, for the purpose of changing or influencing control of Prothena, except for limited nomination-related activities cited.

Which Rubric fund holds more than 5% of Prothena (PRTA) shares?

The disclosure notes that Rubric Capital Master Fund LP, one of the Rubric Funds, has the right to receive or direct dividends or sale proceeds from more than 5% of Prothena’s ordinary shares, reflecting a significant economic interest managed by Rubric Capital.