Prothena (NASDAQ: PRTA) 10% owner adds 100,000 ordinary shares

Rhea-AI Filing Summary

PROTHENA CORP PUBLIC LTD CO major shareholder William P. Scully reported an open-market purchase of 100,000 ordinary shares of PRTA at a weighted average price of $9.813 per share. After this transaction, he directly held 836,000 ordinary shares.

The filing also lists indirect holdings of 52,000 shares held by his spouse and 80,000 shares held by Manatee Equity Fund LLC. A footnote states that he disclaims beneficial ownership of certain securities except to the extent of his pecuniary interest.

Insights

Insider trading analyst

Large shareholder makes substantial open-market PRTA share purchase.

Major shareholder William P. Scully, identified as a ten percent owner, executed an open-market purchase of 100,000 Prothena ordinary shares at a weighted average price of $9.813 per share. This is a direct, discretionary buy rather than an option exercise or tax-related event.

Following the trade, his directly held position increased to 836,000 ordinary shares, with additional indirect holdings reported through his spouse and Manatee Equity Fund LLC. A footnote notes he disclaims beneficial ownership of certain securities except for his pecuniary interest, which is a common legal clarification for indirect holdings.

The filing shows a net-buy of 100,000 shares with no reported sales or derivative exercises in this report. There is no reference to a Rule 10b5-1 trading plan in the provided text, so the transaction appears as a straightforward open-market purchase based on the available information.

Insider Trade Summary

Net Buyer: 100,000 shares

Net Buy 3 txns

Insider SCULLY WILLIAM P

Role 10% Owner

Bought 100,000 shs ($981K)

Type	Security	Shares	Price	Value
Purchase	Ordinary Shares, par value $0.01 per share	100,000	$9.813	$981K
holding	Ordinary Shares, par value $0.01 per share	--	--	--
holding	Ordinary Shares, par value $0.01 per share	--	--	--

Holdings After Transaction: Ordinary Shares, par value $0.01 per share — 836,000 shares (Direct); Ordinary Shares, par value $0.01 per share — 80,000 shares (Indirect, By Manatee Equity Fund LLC); Ordinary Shares, par value $0.01 per share — 52,000 shares (Indirect, By Spouse)

Footnotes (2)

1. F1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.5499 to $9.9750, inclusive. The reporting person undertakes to provide to Prothena Corp Public Ltd Co, any security holder of Prothena Corp Public Ltd Co, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (1) to this Form 4.
2. F2. The reporting person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.

Key Figures

Shares purchased: 100,000 shares Weighted average purchase price: $9.813 per share Direct holdings after transaction: 836,000 shares +3 more

6 metrics

Shares purchased 100,000 shares Open-market purchase on 2026-05-22

Weighted average purchase price $9.813 per share Ordinary shares, par value $0.01

Direct holdings after transaction 836,000 shares Ordinary shares held directly after buy

Spouse indirect holdings 52,000 shares Ordinary shares held indirectly by spouse

Manatee Equity Fund LLC holdings 80,000 shares Ordinary shares held indirectly via LLC

Price range of trades $9.5499–$9.9750 Multiple transactions underlying weighted average

Key Terms

open-market purchase, beneficial ownership, pecuniary interest, ten percent owner

4 terms

open-market purchase financial

"transaction_action is described as an open-market purchase"

An open-market purchase is when an investor or a company buys shares on a public stock exchange at the going market price, rather than through a private deal. It matters to investors because these purchases change how many shares are available, can push the stock price up or signal confidence from large buyers, and often affect per-share metrics like earnings—think of it like someone buying lots of apples off a grocery shelf, reducing supply and potentially raising the price.

beneficial ownership financial

"The reporting person disclaims beneficial ownership of these securities"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

pecuniary interest financial

"disclaims beneficial ownership ... except to the extent of his pecuniary interest"

ten percent owner financial

"reporting person is indicated as a ten percent owner"

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

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Form 4 Insider Transactions: What Each Field Means →

Accepted by SEC EDGAR 05/26/2026 - 02:51 PM Learn about SEC filing dates

FAQ

What did Prothena (PRTA) insider William P. Scully report in this Form 4?

He reported buying 100,000 Prothena ordinary shares in an open-market transaction at a weighted average price of $9.813 per share. After the purchase, his directly held stake increased to 836,000 ordinary shares, plus additional indirect holdings reported in the filing.

How many Prothena (PRTA) shares does William P. Scully hold after the reported transaction?

After the reported transaction, he directly holds 836,000 ordinary shares of Prothena. The filing also lists 52,000 shares held indirectly by his spouse and 80,000 shares held indirectly by Manatee Equity Fund LLC, in which he notes limited beneficial ownership.

At what price did the Prothena (PRTA) insider purchase shares in this filing?

The weighted average purchase price was $9.813 per Prothena ordinary share. A footnote explains these shares were bought in multiple trades at prices ranging from $9.5499 to $9.9750, and detailed trade breakdowns are available on request from the reporting person.

Does the Prothena (PRTA) Form 4 show insider buying or selling?

The Form 4 shows insider buying, with a net purchase of 100,000 ordinary shares coded as an open-market transaction. The transaction summary indicates one buy transaction, no sales, and no derivative exercises or tax-related dispositions in this particular report.

What indirect Prothena (PRTA) holdings are disclosed for William P. Scully?

The filing lists 52,000 Prothena ordinary shares held indirectly through his spouse and 80,000 shares held indirectly via Manatee Equity Fund LLC. A footnote states he disclaims beneficial ownership of certain securities except to the extent of his pecuniary interest.

SEC Form 4

FORM 4

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

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

SCULLY WILLIAM P

(Last) (First) (Middle)

771 MANATEE COVE

(Street)

VERO BEACH FLORIDA 32963

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
PROTHENA CORP PUBLIC LTD CO [ PRTA ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/22/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Ordinary Shares, par value $0.01 per share	05/22/2026		P		100,000	A	$9.813(1)	836,000	D
Ordinary Shares, par value $0.01 per share								80,000	I	By Manatee Equity Fund LLC(2)
Ordinary Shares, par value $0.01 per share								52,000	I	By Spouse

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.5499 to $9.9750, inclusive. The reporting person undertakes to provide to Prothena Corp Public Ltd Co, any security holder of Prothena Corp Public Ltd Co, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (1) to this Form 4.

2. The reporting person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.

	Reid E. Buchanan by POA from William P. Scully	05/26/2026
	** Signature of Reporting Person	Date
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.
* Form 4: SEC 1474 (03-26)