Prothena holder buys 100K shares at $8.43

For PROTHENA CORP PUBLIC LTD CO (PRTA), ten percent owner William P. Scully purchased 100,000 ordinary shares on September 18, 2026 at a weighted average price of $8.4346 per share, with individual purchase prices ranging from $8.3350 to $8.4829.

Rhea-AI Filing Summary

For PROTHENA CORP PUBLIC LTD CO (PRTA), ten percent owner William P. Scully purchased 100,000 ordinary shares on September 18, 2026 at a weighted average price of $8.4346 per share, with individual purchase prices ranging from $8.3350 to $8.4829. After this open-market purchase, he directly holds 927,000 shares, and also reports indirect holdings of 83,500 shares by Manatee Equity Fund LLC and 52,000 shares held by his spouse, with beneficial ownership of the Manatee Equity Fund LLC position disclaimed except to the extent of his pecuniary interest. No Rule 10b5-1 trading plan is reported for these transactions.

Insider Trade Summary

Net Buyer: 100,000 shares

Net Buy 3 txns

Insider SCULLY WILLIAM P

Role 10% Owner

Bought 100,000 shs ($843K)

Type	Security	Shares	Price	Value
Purchase	Ordinary Shares, par value $0.01 per share F1	100,000	$8.4346	$843K
holding	Ordinary Shares, par value $0.01 per share F2	--	--	--
holding	Ordinary Shares, par value $0.01 per share	--	--	--

Holdings After Transaction: Ordinary Shares, par value $0.01 per share — 927,000 shares (Direct); Ordinary Shares, par value $0.01 per share — 83,500 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 $8.3350 to $8.4829, 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: $8.4346 per share Price range of purchases: $8.3350 to $8.4829 per share +3 more

6 metrics

Shares purchased 100,000 shares Ordinary shares bought on September 18, 2026

Weighted average purchase price $8.4346 per share Open-market purchase on September 18, 2026

Price range of purchases $8.3350 to $8.4829 per share Individual trade prices within the reported transaction

Direct holdings after transaction 927,000 shares Direct ownership following the September 18, 2026 purchase

Indirect holdings via Manatee Equity Fund LLC 83,500 shares Reported indirect ownership with beneficial ownership disclaimed except for pecuniary interest

Indirect holdings by spouse 52,000 shares Shares reported as held indirectly by spouse

Key Terms

weighted average price, beneficial ownership, pecuniary interest

3 terms

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

beneficial ownership regulatory

"The reporting person disclaims beneficial ownership of these securities except"

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

"except to the extent of his pecuniary interest therein."

FAQ

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

What insider transaction did PRTA’s William P. Scully report?

William P. Scully reported purchasing 100,000 Prothena (PRTA) ordinary shares on September 18, 2026 in an open-market transaction at a weighted average price of $8.4346 per share, with individual prices between $8.3350 and $8.4829.

What are William P. Scully’s total reported PRTA share holdings after this Form 4?

After the reported transaction, William P. Scully directly owns 927,000 PRTA ordinary shares and reports indirect ownership of 83,500 shares through Manatee Equity Fund LLC and 52,000 shares held by his spouse.

At what prices did William P. Scully buy PRTA shares on September 18, 2026?

The Form 4 states a weighted average purchase price of $8.4346 per PRTA share, with the individual trades executed at prices ranging from $8.3350 to $8.4829, inclusive.

Does the PRTA Form 4 indicate trades under a Rule 10b5-1 trading plan?

No. The Form 4 for Prothena (PRTA) indicates no Rule 10b5-1 trading plan for the reported transactions; the document-level checkbox for such a plan is not marked as affirmative.

How are PRTA shares held through Manatee Equity Fund LLC treated in this Form 4?

The Form 4 reports 83,500 PRTA shares held indirectly through Manatee Equity Fund LLC, and includes a statement that the reporting person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest.

Are any PRTA shares in this Form 4 held by William P. Scully’s spouse?

Yes. The filing lists 52,000 PRTA ordinary shares as held indirectly by his spouse, reported as an indirect ownership line separate from his direct holdings and the Manatee Equity Fund LLC position.

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

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Available on EDGAR 09/21/2026 - 04:25 PM Accepted by SEC EDGAR 09/21/2026 - 04:23 PM Learn about SEC filing dates

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)
09/18/2026

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	09/18/2026		P		100,000	A	$8.4346(1)	927,000	D
Ordinary Shares, par value $0.01 per share								83,500	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 $8.3350 to $8.4829, 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	09/21/2026
	** 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)