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  4. [Form 4] PROTHENA CORP PUBLIC LTD CO Insider Trading Activity

Prothena Corp (PRTA) counsel trades shares in Rule 10b5-1 planned sale

Filing Impact
(Moderate)
Filing Sentiment
(Negative)
Form Type
4

Rhea-AI Filing Summary

PROTHENA CORP PUBLIC LTD CO General Counsel & Company Secretary Michael John Isaacs reported two transactions in ordinary shares. On July 29, 2026, he sold 8,386 shares in open-market or private trades at a weighted average of $8.4731 per share under a Rule 10b5-1 trading plan adopted on April 3, 2026. The trades were executed in multiple transactions at prices ranging from $8.40 to $8.65. On July 28, 2026, 4,694 shares were disposed of at $8.56 per share to satisfy exercise-price or tax-liability obligations by delivering or withholding shares. All transactions involved direct holdings.

Positive

  • None.

Negative

  • None.
Insider Isaacs Michael John
Role General Counsel & Company Sec.
Sold 8,386 shs ($71K)
Type Security Shares Price Value
Sale Ordinary Shares, par value $0.01 per share F1, F2 8,386 $8.4731 $71K
Exercise Price or Tax Liability Ordinary Shares, par value $0.01 per share 4,694 $8.56 $40K
Holdings After Transaction: Ordinary Shares, par value $0.01 per share — 35,745 shares (Direct)
Footnotes (2)
  1. F1. The transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on April 3, 2026.
  2. F2. The transaction was executed in multiple trades in prices ranging from $8.40 to $8.65, inclusive. The price reported in Column 4 above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide to the Securities and Exchange Commission staff, the Issuer, or a security holder of the Issuer, upon request, full information regarding the number of shares sold at each respective price within the range set forth in this footnote.
Shares sold 8,386 shares Ordinary shares sold on July 29, 2026 in open-market or private transactions
Weighted average sale price $8.4731 per share Average price for 8,386 shares sold on July 29, 2026
Shares disposed for tax or exercise obligations 4,694 shares Shares delivered or withheld on July 28, 2026 to satisfy obligations
Disposition price for tax or exercise obligations $8.56 per share Price for 4,694 shares disposed on July 28, 2026
Net buy/sell shares -8,386 shares Net effect of buy/sell transactions excluding tax-liability disposition
Rule 10b5-1 plan adoption date April 3, 2026 Plan governing the July 29, 2026 sale transaction
Rule 10b5-1 trading plan regulatory
"The transaction was effected pursuant to a Rule 10b5-1 trading plan"
A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.
weighted average sale price financial
"The price reported in Column 4 above reflects the weighted average sale price"
exercise price or tax liability financial
"Payment of exercise price or tax liability by delivering or withholding securities"
Ordinary Shares financial
"Ordinary Shares, par value $0.01 per share"
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.

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

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FAQ

What insider sale did Prothena (PRTA) report on July 29, 2026?
Prothena reported that General Counsel Michael John Isaacs sold 8,386 ordinary shares on July 29, 2026, in open-market or private transactions at a weighted average price of $8.4731 per share, executed across multiple trades between $8.40 and $8.65.

Was the recent Prothena (PRTA) insider sale made under a Rule 10b5-1 plan?
Yes. The July 29, 2026 sale of 8,386 ordinary shares by Michael John Isaacs was effected under a Rule 10b5-1 trading plan adopted on April 3, 2026, indicating the transactions were pre-arranged rather than discretionary at the time of execution.

What was the second transaction reported by Prothena (PRTA) on July 28, 2026?
On July 28, 2026, Michael John Isaacs had 4,694 ordinary shares disposed of at $8.56 per share to satisfy exercise-price or tax-liability obligations by delivering or withholding shares, rather than through an open-market sale. These shares were held directly.

How many Prothena (PRTA) shares did the insider sell versus tax-withheld?
Michael John Isaacs sold 8,386 shares in open-market or private transactions and had an additional 4,694 shares disposed of to cover exercise-price or tax-liability obligations, according to the Form 4 summary of his non-derivative ordinary share transactions.

Who is the Prothena (PRTA) insider involved in these Form 4 transactions?
The Form 4 lists Michael John Isaacs, General Counsel & Company Secretary of Prothena, as the reporting person. He reported one open-market or private sale of 8,386 shares and one tax- or exercise-related share disposition of 4,694 shares, both from direct holdings.
SEC Form 4
FORM 4UNITED 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).
X
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*
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. Issuer Name and Ticker or Trading Symbol
PROTHENA CORP PUBLIC LTD CO [ PRTA ] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
Director10% Owner
XOfficer (give title below)Other (specify below)
General Counsel & Company Sec.
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
07/28/2026		6. Individual or Joint/Group Filing (Check Applicable Line)
XForm 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)
CodeVAmount(A) or (D)Price
Ordinary Shares, par value $0.01 per share07/28/2026F4,694D$8.5644,131D
Ordinary Shares, par value $0.01 per share07/29/2026S(1)8,386D$8.4731(2)35,745D
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)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Explanation of Responses:
1. The transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on April 3, 2026.
2. The transaction was executed in multiple trades in prices ranging from $8.40 to $8.65, inclusive. The price reported in Column 4 above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide to the Securities and Exchange Commission staff, the Issuer, or a security holder of the Issuer, upon request, full information regarding the number of shares sold at each respective price within the range set forth in this footnote.
/s/ Michael J. Isaacs07/30/2026
** 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 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)

Source: View Original Filing on SEC EDGAR