BlackRock (PRTA holder) discloses 6.9% beneficial stake in Prothena common stock

Rhea-AI Filing Summary

BlackRock, Inc. reports beneficial ownership of common stock of Prothena Corporation plc on an amended Schedule 13G. BlackRock reports beneficial ownership of 3,587,480 shares of Prothena common stock, representing 6.9% of the outstanding class.

BlackRock has sole voting power over 3,533,090 shares and sole dispositive power over 3,587,480 shares, with no shared voting or dispositive power. Various underlying clients have rights to dividends or sale proceeds, but no single client holds more than five percent of Prothena’s outstanding common shares.

Key Figures

Beneficial ownership: 3,587,480 shares Percent of class: 6.9% Sole voting power: 3,533,090 shares +4 more

7 metrics

Beneficial ownership 3,587,480 shares Shares of Prothena common stock beneficially owned by BlackRock

Percent of class 6.9% Percentage of Prothena common stock class beneficially owned

Sole voting power 3,533,090 shares Shares over which BlackRock has sole power to vote

Shared voting power 0 shares Shares over which BlackRock has shared power to vote

Sole dispositive power 3,587,480 shares Shares over which BlackRock has sole power to dispose

Shared dispositive power 0 shares Shares over which BlackRock has shared power to dispose

Filing date 07/29/2026 Date the amended Schedule 13G was signed by BlackRock

Key Terms

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

5 terms

beneficially owned financial

"this reflects the securities beneficially owned, or deemed to be beneficially owned"

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 voting power financial

"Sole Voting Power 3,533,090.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"Sole Dispositive Power 3,587,480.00"

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.

Schedule 13G regulatory

"In accordance with SEC Release No. 34-39538 this reflects the securities"

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.

percent of class financial

"Percent of class: 6.9 %"

Percent of class is the portion of a specific category of securities—such as a company’s common shares, preferred shares, or a bond series—that takes part in or approves a corporate action (vote, consent, tender, etc.). Investors watch this number because it reveals how much support or opposition exists within that particular shareholder group; like counting how many members of a club back a proposal, it can determine whether a plan passes or how influence is distributed.

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

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Available on EDGAR 07/29/2026 - 03:21 PM Accepted by SEC EDGAR 07/29/2026 - 03:19 PM Learn about SEC filing dates

FAQ

What percentage of Prothena (PRTA) does BlackRock currently report owning?

BlackRock reports beneficial ownership of 6.9% of Prothena’s common stock. This corresponds to 3,587,480 shares as disclosed in the amended Schedule 13G filing.

How many Prothena (PRTA) shares does BlackRock have sole voting power over?

BlackRock has sole voting power over 3,533,090 shares of Prothena common stock. It reports no shared voting power in the Schedule 13G/A.

What is the total number of Prothena (PRTA) shares BlackRock beneficially owns?

BlackRock beneficially owns 3,587,480 shares of Prothena common stock. This total aligns with the shares over which it has sole dispositive power in the filing.

Does any single BlackRock client own more than 5% of Prothena (PRTA)?

No single underlying client associated with BlackRock has an interest of more than 5% of Prothena’s outstanding common shares. Rights to dividends and sale proceeds are spread across various persons.

What type of filing did BlackRock submit for its Prothena (PRTA) holdings?

BlackRock submitted an amended Schedule 13G (Schedule 13G/A) reporting its beneficial ownership in Prothena common stock, including voting and dispositive power details.

Who signed the BlackRock ownership report for Prothena (PRTA) and when?

The report was signed by Spencer Fleming, Managing Director at BlackRock, on 07/29/2026. The signature confirms the disclosed ownership information.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 11)

PROTHENA CORPORATION PUBLIC LIMITED COMPANY

(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

BlackRock, Inc.

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 3,533,090.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 3,587,480.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

3,587,480.00

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)

6.9 %

12

Type of Reporting Person (See Instructions)

HC

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 Ireland D02 VK60
Item 2.
(a)	Name of person filing: BlackRock, Inc. In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by certain business units (collectively, the "Reporting Business Units") of BlackRock, Inc. and its subsidiaries and affiliates. It does not include securities, if any, beneficially owned by other business units whose beneficial ownership of securities are disaggregated from that of the Reporting Business Units in accordance with such release.
(b)	Address or principal business office or, if none, residence: BlackRock, Inc., 50 Hudson Yards New York, NY 10001
(c)	Citizenship: See Item 4 of Cover Page
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: G72800108
Item 4.	Ownership
(a)	Amount beneficially owned: 3587480
(b)	Percent of class: 6.9 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 3533090
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 3587480
	(iv) Shared power to dispose or to direct the disposition of: 0
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. Various persons 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 CORPORATION PUBLIC LIMITED COMPANY. No one person's interest in the common stock of PROTHENA CORPORATION PUBLIC LIMITED COMPANY is more than five percent of the total outstanding common shares.
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 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.

BlackRock, Inc.

Signature:	Spencer Fleming
Name/Title:	Managing Director
Date:	07/29/2026

Exhibit Information

Exhibit 24: Power of Attorney Exhibit 99: Item 7