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Prothena (NASDAQ: PRTA) counsel details ordinary share and option stakes

Filing Impact
(Neutral)
Filing Sentiment
(Neutral)
Form Type
3

Rhea-AI Filing Summary

Prothena Corp Public Ltd Co General Counsel & Company Secretary Michael John Isaacs has reported his initial holdings. He directly owns 48,825 ordinary shares. He also holds several stock options over ordinary shares at exercise prices ranging from $10.99 to $52.97, with expiration dates between 2030 and 2036.

Certain options are already fully vested, while others vest 25% on specific dates and then in equal monthly installments, in each case subject to his continued employment with the company.

Positive

  • None.

Negative

  • None.
Insider Isaacs Michael John
Role General Counsel & Company Sec.
Type Security Shares Price Value
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Stock Option (Right to Buy) -- -- --
holding Ordinary Shares, par value $0.01 per share -- -- --
Holdings After Transaction: Stock Option (Right to Buy) — 17,500 shares (Direct, null); Ordinary Shares, par value $0.01 per share — 48,825 shares (Direct, null)
Footnotes (1)
  1. The option is fully vested. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 2, 2024, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on February 27, 2025, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 5, 2026, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date. The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on March 3, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date. The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on April 10, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
Direct ordinary shares 48,825 shares Directly owned ordinary shares reported on Form 3
Option grant 1 50,000 shares at $10.50 Stock option over ordinary shares, expires 2036-04-10
Option grant 2 37,500 shares at $9.36 Stock option over ordinary shares, expires 2036-03-03
Option grant 3 8,612 shares at $14.95 Stock option over ordinary shares, expires 2035-03-05
Option grant 4 12,000 shares at $30.30 Stock option over ordinary shares, expires 2034-02-27
Option grant 5 17,500 shares at $10.99 Stock option over ordinary shares, expires 2030-04-01
Stock Option (Right to Buy) financial
"security_title": "Stock Option (Right to Buy)""
Ordinary Shares financial
"underlying_security_title": "Ordinary Shares""
Ordinary shares are a type of ownership stake in a company, giving shareholders a right to participate in the company’s profits and decision-making through voting. They are similar to owning a piece of a business, and their value can rise or fall based on the company's performance. Investors buy ordinary shares to potentially earn dividends and benefit from the company's growth over time.
exercise price financial
"conversion_or_exercise_price": "10.5000""
The exercise price is the fixed amount at which you can buy or sell an asset, like a stock, when using an options contract. It matters because it helps determine whether exercising the option will be profitable or not, depending on the current market price. Think of it as the set price you agree on today to buy or sell later.
expiration date financial
"expiration_date": "2036-04-10T00:00:00.000Z""
The expiration date is the deadline after which a financial contract, such as an option or a futures agreement, is no longer valid or can be exercised. It matters to investors because it determines the timeframe during which they can take action or benefit from the contract, similar to how a coupon or a food item has a limited period of usefulness. Once the expiration date passes, the contract loses its value or ability to be used.
vest and become exercisable financial
"The shares subject to the option vested and became exercisable as to 25%"
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SEC Form 3
FORM 3UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

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:3235-0104
Estimated average burden
hours per response:0.5
1. Name and Address of Reporting Person*
Isaacs Michael John

(Last)(First)(Middle)
C/O PROTHENA BIOSCIENCES INC.
1800 SIERRA POINT PARKWAY

(Street)
BRISBANE CALIFORNIA 94005

(City)(State)(Zip)

UNITED STATES

(Country)
2. Date of Event Requiring Statement (Month/Day/Year)
06/08/2026
3. Issuer Name and Ticker or Trading Symbol
PROTHENA CORP PUBLIC LTD CO [ PRTA ]
3a. Foreign Trading Symbol
5. If Amendment, Date of Original Filed (Month/Day/Year)
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
Director10% Owner
XOfficer (give title below)Other (specify below)
General Counsel & Company Sec.
6. Individual or Joint/Group Filing (Check Applicable Line)
XForm filed by One Reporting Person
Form filed by More than One Reporting Person
Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5)
Ordinary Shares, par value $0.01 per share48,825D
Table II - Derivative Securities Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4) 2. Date Exercisable and Expiration Date (Month/Day/Year)3. Title and Amount of Securities Underlying Derivative Security (Instr. 4) 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 6. Nature of Indirect Beneficial Ownership (Instr. 5)
Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock Option (Right to Buy) (1)04/01/2030Ordinary Shares17,500$10.99D
Stock Option (Right to Buy) (1)02/25/2031Ordinary Shares10,000$22.6D
Stock Option (Right to Buy) (1)02/23/2032Ordinary Shares8,250$32.45D
Stock Option (Right to Buy) (2)03/02/2033Ordinary Shares8,800$52.97D
Stock Option (Right to Buy) (3)02/27/2034Ordinary Shares12,000$30.3D
Stock Option (Right to Buy) (4)03/05/2035Ordinary Shares8,612$14.95D
Stock Option (Right to Buy) (5)03/03/2036Ordinary Shares37,500$9.36D
Stock Option (Right to Buy) (6)04/10/2036Ordinary Shares50,000$10.5D
Explanation of Responses:
1. The option is fully vested.
2. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 2, 2024, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
3. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on February 27, 2025, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
4. The shares subject to the option vested and became exercisable as to 25% of the total number of shares subject to the option on March 5, 2026, and vest and become exercisable with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
5. The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on March 3, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
6. The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on April 10, 2027, and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date.
Remarks:
Exhibit List: Exhibit 24 - Power of Attorney
/s/ Michael J. Isaacs06/12/2026
** Signature of Reporting PersonDate
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 5 (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 3: SEC 1473 (03-26)

FAQ

What does Prothena (PRTA) General Counsel Michael John Isaacs report on this Form 3?

He reports his initial ownership in Prothena, including 48,825 directly held ordinary shares and multiple stock option awards. These options give him the right to buy additional ordinary shares at preset prices before their respective expiration dates.

How many Prothena (PRTA) ordinary shares does Michael John Isaacs directly own?

He directly owns 48,825 ordinary shares of Prothena. This figure represents his reported direct equity stake in the company’s ordinary shares as of the Form 3 reporting date, separate from any additional shares underlying his stock options.

What are the key stock option positions held by Prothena (PRTA) General Counsel Isaacs?

He holds several stock options, including options over 50,000 ordinary shares at a $10.50 exercise price expiring in 2036, and 37,500 shares at $9.36 expiring in 2036, plus additional grants with higher exercise prices and earlier expiration dates.

How do Michael John Isaacs’s Prothena (PRTA) stock options vest over time?

Some options are fully vested, while others vest 25% on specific initial vesting dates and then in 1/48th monthly installments. Each vesting schedule is conditioned on his continued employment with Prothena on the relevant vesting dates.

Do the reported Prothena (PRTA) holdings reflect any recent share purchases or sales by Isaacs?

The filing characterizes the entries as holdings, with no buy or sell transactions identified. It lists his existing ordinary share ownership and outstanding stock options rather than reporting new open‑market purchases or sales.