Ten percent owner of Prothena (NASDAQ: PRTA) acquires 125,000 shares in open-market buy

Rhea-AI Filing Summary

Prothena Corp Public Ltd Co insider William P. Scully, a ten percent owner, bought 125,000 ordinary shares in an open-market purchase at a weighted average price of $8.1698 per share. The trade on June 11, 2026 increased his direct holdings to 1,061,000 ordinary shares.

The filing notes the shares were purchased in multiple transactions at prices ranging from $7.84 to $8.43 per share. It also reports additional indirect holdings of 52,000 shares held by his spouse and 80,000 shares held by Manatee Equity Fund LLC. Scully disclaims beneficial ownership of certain reported securities except to the extent of his pecuniary interest in them.

Insights

Equity analyst

Ten percent owner makes sizable open-market share purchase, signaling increased direct exposure.

William P. Scully, identified as a ten percent owner of Prothena, completed an open-market purchase of 125,000 ordinary shares at a weighted average price of $8.1698 on June 11, 2026. Following the trade, his directly held position rose to 1,061,000 shares.

The transaction is a straightforward open-market buy, a strong-signal insider action compared with grants or tax-related dispositions. The filing also lists 52,000 shares held indirectly by his spouse and 80,000 shares held by Manatee Equity Fund LLC, with a disclaimer of beneficial ownership except for his pecuniary interest.

Because there are no derivatives exercised and no sales, the net effect is an increase in equity exposure. While insider purchases are often viewed as a constructive sign, this single transaction does not, by itself, redefine Prothena’s broader investment thesis and is best interpreted alongside future company disclosures.

Insider Trade Summary

Net Buyer: 125,000 shares ($1,021,225)

Net Buy 3 txns

Insider SCULLY WILLIAM P

Role null

Bought 125,000 shs ($1.02M)

Type	Security	Shares	Price	Value
Purchase	Ordinary Shares, par value $0.01 per share	125,000	$8.1698	$1.02M
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 — 1,061,000 shares (Direct, null); Ordinary Shares, par value $0.01 per share — 80,000 shares (Indirect, By Manatee Equity Fund LLC)

Footnotes (1)

1. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $7.8400 to $8.4300, 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. The reporting person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.

Key Figures

Shares purchased: 125,000 shares Purchase price: $8.1698 per share Price range: $7.84–$8.43 per share +3 more

6 metrics

Shares purchased 125,000 shares Open-market purchase on June 11, 2026

Purchase price $8.1698 per share Weighted average price for 125,000 shares

Price range $7.84–$8.43 per share Range of individual trade prices in the purchase

Direct holdings after transaction 1,061,000 shares Ordinary shares directly owned by insider after purchase

Indirect holdings by spouse 52,000 shares Ordinary shares held indirectly through spouse

Indirect holdings by Manatee Equity Fund LLC 80,000 shares Ordinary shares held indirectly through Manatee Equity Fund LLC

Key Terms

weighted average price, open-market purchase, beneficial ownership, ten percent owner

4 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.

open-market purchase financial

"transaction_action: 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 regulatory

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

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.

ten percent owner regulatory

"reporting person is marked as a ten percent owner."

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Form 4 Insider Transactions: What Each Field Means →

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)
06/11/2026

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	06/11/2026		P		125,000	A	$8.1698(1)	1,061,000	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 $7.8400 to $8.4300, 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	06/12/2026
	** 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)

FAQ

What insider transaction did PRTA ten percent owner William P. Scully report?

William P. Scully reported buying 125,000 Prothena (PRTA) ordinary shares in an open-market transaction. The weighted average purchase price was $8.1698 per share, executed on June 11, 2026, increasing his directly owned stake to 1,061,000 shares.

At what prices did the PRTA insider purchase his 125,000 shares?

The 125,000 Prothena (PRTA) shares were bought at a weighted average price of $8.1698. According to the filing, individual trades occurred in a range between $7.84 and $8.43 per share, reflecting multiple executions within that band.

How many Prothena (PRTA) shares does the insider own after this Form 4 transaction?

After the reported transaction, William P. Scully directly owns 1,061,000 Prothena (PRTA) ordinary shares. The filing also notes 52,000 shares held indirectly by his spouse and 80,000 shares held indirectly by Manatee Equity Fund LLC.

Were there any Prothena (PRTA) insider share sales reported in this Form 4?

No share sales were reported. The Form 4 shows an open-market purchase of 125,000 Prothena (PRTA) shares, plus two entries that update indirect holdings. The transaction summary indicates net-buy activity, with no selling transactions disclosed.

What indirect Prothena (PRTA) holdings related to the insider are disclosed?

The filing discloses 52,000 Prothena (PRTA) shares held indirectly through the insider’s spouse and 80,000 shares held indirectly through Manatee Equity Fund LLC. It states that the reporting person disclaims beneficial ownership of certain securities except to the extent of his pecuniary interest.

Does the PRTA insider filing mention a Rule 10b5-1 trading plan?

The disclosed text does not reference any Rule 10b5-1 trading plan. The Form 4 characterizes the 125,000-share transaction as an open-market purchase with a weighted average price and specified price range, without indicating it was executed under a pre-arranged plan.