Prothena Corp Public Ltd: William P. Scully filed an amended Schedule 13G/A reporting beneficial ownership of 5,378,846 Ordinary Shares, representing approximately 10.27% of the company's 52,353,237 shares outstanding as of April 30, 2026. The filing breaks ownership into positions with 793,000 shares of sole voting/dispositive power and 4,585,846 shares of shared voting/dispositive power.
Positive
None.
Negative
None.
Insights
Holder reports a significant ~10% position with mixed voting control.
The filing states the reporting person may be deemed beneficial owner of 5,378,846 Ordinary Shares, or 10.27% of outstanding shares as of April 30, 2026. Ownership aggregates direct IRA holdings, manager-controlled LLC interests, and trust-related positions.
Control features are mixed: 793,000 shares are held with sole voting/dispositive power while 4,585,846 are shared. Subsequent disclosures may clarify voting arrangements or transfers; current filings anchor the position to the cited share counts and ownership mechanisms.
Schedule 13G/A updates beneficial ownership and cites specific trust/IRA holdings.
The filing itemizes constituent holdings including a manager-controlled LLC, multiple IRAs, and grantor retained annuity trusts, and notes shared powers arising from retained rights to substitute assets. The filing is signed by an attorney-in-fact on 05/11/2026.
Regulatory readers should note the filing format (amendment) and the explicit outstanding-share anchor: 52,353,237 shares as of April 30, 2026. No transaction timing or changes in percentage ownership beyond the amendment language are provided.
Key Figures
Beneficial ownership:5,378,846 sharesPercent of class:10.27%Shares outstanding:52,353,237 shares+3 more
6 metrics
Beneficial ownership5,378,846 sharesAggregate holding reported in Schedule 13G/A
Percent of class10.27%Calculated using shares outstanding as of <date>April 30, 2026</date>
Shares outstanding52,353,237 sharesIssuer's Form 10-Q for quarter ended <date>March 31, 2026</date> (as of April 30, 2026)
Sole voting power793,000 sharesShares with sole voting/dispositive power reported by the filer
Shared voting power4,585,846 sharesShares with shared voting/dispositive power reported by the filer
Manatee Equity Fund LLC80,000 sharesOwned by Manatee Equity Fund LLC, managed by the reporting person
"The Reporting Person may be deemed to be the beneficial owner of 5,378,846 Ordinary Shares."
A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.
grantor retained annuity trustsfinancial
"4,470,846 Ordinary Shares owned in the aggregate by various grantor retained annuity trusts"
A grantor retained annuity trust (GRAT) is an estate-planning tool where an owner transfers assets into a trust and receives fixed payments back for a set number of years; any remaining assets after that period pass to designated beneficiaries. For investors it matters because it can move future investment growth to heirs while potentially reducing gift and estate taxes — like putting a rising asset in a timed box that pays you first and gives the remaining upside to others.
dispositive powerregulatory
"Sole Dispositive Power 793,000.00 Shared Dispositive Power 4,585,846.00"
Dispositive power is the authority to decide the final outcome of an asset, legal claim, contract, or corporate action — in effect the power to dispose of or resolve something. For investors it matters because whoever holds that authority can determine who gets paid, who controls an asset or vote, and how risks and returns are allocated; think of it like holding the key that lets you lock in the winner or loser in a deal.
investment management agreementfinancial
"23,000 Ordinary Shares owned by an IRA subject to an investment management agreement"
An investment management agreement is a written contract that hires a professional to make buying, selling and strategy decisions for an investment account or fund, and sets out their duties, fees, risk limits, performance measures and reporting requirements. It matters to investors because the agreement determines who controls the money, how much the service costs, what risks are allowed, and how success or failure is measured—think of it as the service contract that defines expectations and remedies for a hired portfolio manager.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 6)
PROTHENA CORP PUBLIC LTD CO
(Name of Issuer)
Ordinary Shares, $0.01 par value
(Title of Class of Securities)
G72800108
(CUSIP Number)
05/07/2026
(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
SCULLY WILLIAM P
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
FLORIDA
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
793,000.00
6
Shared Voting Power
4,585,846.00
7
Sole Dispositive Power
793,000.00
8
Shared Dispositive Power
4,585,846.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,378,846.00
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)
10.3 %
12
Type of Reporting Person (See Instructions)
IN
Comment for Type of Reporting Person: *See Item 4
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
PROTHENA CORP PUBLIC LTD CO
(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:
William P Scully
(b)
Address or principal business office or, if none, residence:
771 Manatee Cove, Vero Beach, Florida 32963
(c)
Citizenship:
Florida
(d)
Title of class of securities:
Ordinary Shares, $0.01 par value
(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 Reporting Person may be deemed to be the beneficial owner of 5,378,846 Ordinary Shares. This amount consists of (i) 80,000 Ordinary Shares owned by Manatee Equity Fund LLC, of which the Reporting Person is the sole manager with sole voting and dispositive power, (ii) 713,000 Ordinary Shares owned by the Reporting Persons IRA, over which he has sole voting and dispositive power, (iii) 42,000 Ordinary Shares owned by the Reporting Persons spouses IRA, over which he may be deemed to have shared voting and dispositive power, (iv) 10,000 Ordinary Shares owned by the Reporting Persons spouse, over which he may be deemed to have shared voting and dispositive power (v) 23,000 Ordinary Shares owned by an IRA subject to an investment management agreement over which the Reporting Person may be deemed to have shared voting and dispositive power by reason of his right to terminate such agreement, (vii) 4,470,846 Ordinary Shares owned in the aggregate by various grantor retained annuity trusts, which have an independent trustee, but over which the Reporting Person may be deemed to have shared voting and dispositive power by reason of his retained right to substitute assets in such trusts, and (viii) 40,000 Ordinary Shares owned by another trust, which has an independent trustee, but over which the Reporting Person may be deemed to have shared voting and dispositive power by reason of his retained right to substitute assets in such trust
(b)
Percent of class:
According to the Issuers most recent Quarterly Report on Form 10-Q for the quarter ended March 31, 2026, as filed with the Securities and Exchange Commission on May 7, 2026, the number of shares outstanding as of April 30, 2026 was 52,353,237. The Ordinary Shares which the Reporting Person may be deemed to beneficially own constitute approximately 10.27% of such total number of shares
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
793,000
(ii) Shared power to vote or to direct the vote:
4,585,846
(iii) Sole power to dispose or to direct the disposition of:
793,000
(iv) Shared power to dispose or to direct the disposition of:
4,585,846
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.
Not Applicable
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 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.
What stake does William P. Scully report in PROTHENA (PRTA)?
William P. Scully reports beneficial ownership of 5,378,846 Ordinary Shares, equal to approximately 10.27% of PROTHENA's outstanding shares as of April 30, 2026. The amount is aggregated across LLC, IRA, and trust holdings.
How many Prothena shares were outstanding for the ownership calculation?
The filing cites 52,353,237 shares outstanding as of April 30, 2026. The reported ownership percentage of 10.27% is calculated using this outstanding-share figure disclosed in the issuer's Form 10-Q.
What voting and dispositive powers does the filing show for Scully?
The filing shows 793,000 shares with sole voting and dispositive power and 4,585,846 shares with shared voting and dispositive power. These categories reflect direct management, IRA control, and certain retained rights in trust arrangements.
Which account types and entities contribute to the reported holdings?
Reported holdings include Manatee Equity Fund LLC (80,000), the reporting person’s IRA (713,000), spouse IRA and spouse holdings, an IRA under an investment management agreement (23,000), and multiple trusts totaling 4,510,846 shares.
Who signed the amended Schedule 13G/A for this filing?
The amendment was signed by /s/ Diana L. Hayes, acting as attorney-in-fact, with the signature date shown as 05/11/2026, per the filing's signature block.
