Prothena
Develops investigational protein-dysregulation therapies with a partner-heavy clinical pipeline.
$9.33
After-hours close0.00 (0.00%)
At close$9.33(+2.64%)
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Breakdown13F · Form 4
Institutions 90.96%47.62M sharesInsiders 0.80%417.3K sharesOther 8.24%4.31M shares
Shares outstanding 52.35M · Float 46.55M · 88.9% free float
Institutions13F, as of Jun 30, 2026
197 holders · 47.62M shares · 31 new positions · 90 increased · 57 reduced · 24 closed
| Holder | Shares | % outstanding | Chg q/q | Filed |
|---|---|---|---|---|
| FMR LLC | 7.20M | 13.75% | −352.0K | Aug 13, 2026 |
| Rubric Capital Management LP | 5.00M | 9.55% | 0 | Aug 14, 2026 |
| BlackRock, Inc. | 4.87M | 9.30% | +223.8K | Aug 7, 2026 |
| State Street Corp | 2.39M | 4.57% | +454.9K | Aug 7, 2026 |
| Acadian Asset Management LLC | 2.01M | 3.84% | +463.1K | Aug 13, 2026 |
| Vanguard Portfolio Management LLC | 1.65M | 3.15% | +205.3K | Aug 13, 2026 |
| D. E. Shaw & Co., Inc. | 1.61M | 3.08% | −151.9K | Aug 14, 2026 |
| Adar1 Capital Management, LLC | 1.55M | 2.97% | −26.9K | Aug 14, 2026 |
Beneficial owners13D/G · 5% or more, as filed
| Holder | % of class | Shares | Form | Filed |
|---|---|---|---|---|
| Scully William P | 10.30% | 5.38M | 13G | May 11, 2026 ↗ |
| Rubric Capital Management LP | 9.29% | 5.00M | 13G | May 15, 2026 ↗ |
| Fennell Todd W. | 8.40% | 4.50M | 13G | Nov 12, 2025 ↗ |
| BlackRock, Inc. | 5.70% | 3.09M | 13G | Oct 17, 2025 ↗ |
InsidersForm 4
| Insider | Role | Shares | % outstanding | Filed |
|---|---|---|---|---|
| EcoR1 Capital, LLC | 10 percent owner | 5.30M | 10.13% | May 6, 2025 |
| Scully William P | 10 percent owner | 883.5K | 1.69% | Aug 21, 2026 |
| Michael J. Malecek | officer: Chief Legal Officer | 80.0K | 0.15% | Jul 30, 2025 |
| Gene G. Kinney | director, officer: President and CEO | 68.8K | 0.13% | Jul 30, 2026 |
| Anne Evans Kingston | officer: Chief Strategy Officer | 55.8K | 0.11% | Jul 30, 2026 |
| Brandon S. Smith | officer: Chief Operating Officer | 52.0K | 0.10% | Jul 30, 2026 |
| Chad J. Swanson | officer: Chief Development Officer | 40.7K | 0.08% | Jul 30, 2026 |
| Tran Nguyen | officer: Chief Strategy Officer and CFO | 40.2K | 0.08% | Jul 30, 2026 |
| Michael John Isaacs | officer: General Counsel & Company Sec. | 35.7K | 0.07% | Jul 30, 2026 |
| Wagner M. Zago | officer: Chief Scientific Officer | 34.0K | 0.06% | Jul 30, 2026 |
3 ten-percent owners hold 9.37M shares by Form 4 — the 13D/G table above shows those stakes, the figure above counts officers and directors only · 6 people have not refiled in the last 18 months (9.43M shares), so they are not in the figure above
Latest trades
| Date | Insider | Type | Shares | Avg price | Owned after |
|---|---|---|---|---|---|
| Aug 20, 2026 | William P. Scully10 percent owner | Purchase | 50,000 | $8.79 | 800,000 |
| Aug 7, 2026 | William P. Scully10 percent owner | Purchase · 2 lots | 37,500 | $8.62 | 873,500 |
| Jul 29, 2026 | Michael John Isaacsofficer: General Counsel & Company Sec. | Sale | 8,386 | $8.47 | 35,745 |
| Jul 29, 2026 | Anne Evans Kingstonofficer: Chief Strategy Officer | Sale | 7,662 | $8.47 | 55,782 |
| Jun 16, 2026 | William P. Scully10 percent owner | Purchase | 20,000 | $7.90 | 756,000 |
| Jun 11, 2026 | William P. Scully10 percent owner | Purchase | 125,000 | $8.17 | 1,061,000 |
| Jun 4, 2026 | William P. Scully10 percent owner | Purchase | 50,000 | $9.31 | 936,000 |
| Jun 2, 2026 | William P. Scully10 percent owner | Purchase | 50,000 | $9.43 | 886,000 |
| May 22, 2026 | William P. Scully10 percent owner | Purchase | 100,000 | $9.81 | 836,000 |
CongressHouse and Senate disclosures
Not reported.