Form 4: William P. Scully Increases Stake in Prothena Corp

10% owner William P. Scully acquired 50,000 shares of Prothena Corp at a weighted average price of $9.3059.

Summary

• Reporting person William P. Scully purchased 50,000 ordinary shares of Prothena Corp (PRTA) on June 4, 2026.
• The shares were acquired at a weighted average price of $9.3059 per share, with individual transaction prices ranging from $9.1000 to $9.4097.
• Following this transaction, Mr. Scully directly owns 936,000 shares.
• Mr. Scully maintains indirect ownership of an additional 80,000 shares via Manatee Equity Fund LLC and 52,000 shares held by his spouse.

Sentiment

Score: 7

Explanation: StockSavvy.ai views this as a moderately positive signal, as significant open-market buying by a major shareholder typically indicates confidence in the company's future.

Positives

• Insider confidence is demonstrated by a significant open-market purchase of 50,000 shares by a 10% owner.
• The purchase price reflects a range of $9.10 to $9.41, suggesting the insider views the current valuation as attractive.

Negatives

• NA

Risks

• NA

Future Outlook

NA

Industry Context

StockSavvy.ai notes that insider buying in the biotechnology sector is often interpreted by the market as a positive signal regarding the company's clinical pipeline or long-term valuation prospects.

Comparison to Industry Standards

• Insider buying by 10% owners is generally viewed as a stronger signal of conviction than standard executive stock option exercises.

Legal Proceedings

• NA

Related Party Transactions

• The reporting person discloses indirect ownership through Manatee Equity Fund LLC and shares held by his spouse.

Stakeholder Impact

• Shareholders may view the increased stake by a 10% owner as a vote of confidence in the company's strategic direction.

Next Steps

• NA

Key Dates

Keywords

Prothena, PRTA, Insider Trading, William P. Scully, Biotech, SEC Form 4