Prothena Corporation plc (PRTA) Ownership
PRTA ownership summary
as of October 18, 2026- Institutions
- 93.2% of shares outstanding
- Insiders
- 22.56% of shares outstanding
- Shares outstanding
- 51.3M
- Float
- 34.1M shares available to trade
- Short interest
- 18.79% 8.0M shares short
- Days to cover
- 17.58 short interest down 6.2% vs prior month
- Institutions 93.21%
- Insiders 22.56%
PRTA top institutional holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | FMR Inc | 14.02% | 7.2M | $60.1M | −352,000 (−4.7%) | June 30, 2026 |
| 2 | Rubric Capital Management LP | 9.74% | 5.0M | $41.8M | — | June 30, 2026 |
| 3 | BlackRock Inc | 9.48% | 4.9M | $40.6M | +223,795 (+4.8%) | June 30, 2026 |
| 4 | State Street Corp | 4.66% | 2.4M | $20.0M | +454,926 (+23.5%) | June 30, 2026 |
| 5 | Acadian Asset Management LLC | 3.92% | 2.0M | $16.8M | +463,052 (+29.9%) | June 30, 2026 |
| 6 | Vanguard Portfolio Management, LLC | 3.22% | 1.7M | $13.8M | +205,314 (+14.2%) | June 30, 2026 |
| 7 | D. E. Shaw & Co LP | 3.14% | 1.6M | $13.5M | −151,890 (−8.6%) | June 30, 2026 |
| 8 | ADAR1 Capital Management LLC | 3.03% | 1.6M | $13.0M | −26,908 (−1.7%) | June 30, 2026 |
| 9 | Two Sigma Investments LLC | 2.46% | 1.3M | $10.6M | +59,009 (+4.9%) | June 30, 2026 |
| 10 | Palo Alto Investors, LLC | 2.23% | 1.1M | $9.5M | −65,413 (−5.4%) | June 30, 2026 |
| 11 | Geode Capital Management, LLC | 2.19% | 1.1M | $9.4M | +27,711 (+2.5%) | June 30, 2026 |
| 12 | Federated Hermes Inc | 2.11% | 1.1M | $9.1M | +24,552 (+2.3%) | June 30, 2026 |
| 13 | Morgan Stanley - Brokerage Accounts | 1.94% | 995K | $8.3M | −235,100 (−19.1%) | June 30, 2026 |
| 14 | The Goldman Sachs Group Inc | 1.91% | 980K | $8.2M | +160,845 (+19.6%) | June 30, 2026 |
| 15 | Jacobs Levy Equity Management, Inc. | 1.88% | 966K | $8.1M | −6,029 (−0.6%) | June 30, 2026 |
| 16 | Dimensional Fund Advisors, Inc. | 1.76% | 906K | $7.6M | +123,048 (+15.7%) | June 30, 2026 |
| 17 | Qube Research & Technologies | 1.54% | 791K | $6.6M | +176,566 (+28.7%) | June 30, 2026 |
| 18 | Renaissance Technologies Corp | 1.36% | 698K | $5.8M | +90,100 (+14.8%) | June 30, 2026 |
| 19 | Man Group PLC | 1.32% | 678K | $5.7M | +296,542 (+77.7%) | June 30, 2026 |
| 20 | Mariner Wealth Advisors LLC | 1.22% | 625K | $5.2M | +62,013 (+11.0%) | June 30, 2026 |
Value at the latest close. Change = shares bought or sold in the latest quarterly filing (13F). In the top 20, 13 holders added 2.4M shares and 6 cut 837K.
PRTA top mutual fund and ETF holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | Fidelity Growth Company Fund | 4.26% | 2.2M | $18.2M | −43,300 (−1.9%) | August 31, 2026 |
| 2 | iShares Russell 2000 ETF | 2.18% | 1.1M | $9.4M | −12,928 (−1.1%) | September 30, 2026 |
| 3 | State Street® SPDR® S&P® Biotech ETF | 1.77% | 910K | $7.6M | −17,400 (−1.9%) | September 30, 2026 |
| 4 | Vanguard Explorer Inv | 1.48% | 757K | $6.3M | +139,978 (+22.7%) | June 30, 2026 |
| 5 | Fidelity Series Growth Company | 1.41% | 724K | $6.0M | −14,300 (−1.9%) | August 31, 2026 |
| 6 | Fidelity Small Cap Index | 0.95% | 486K | $4.1M | +4,598 (+1.0%) | July 31, 2026 |
| 7 | Fidelity Select Biotechnology | 0.92% | 473K | $3.9M | −9,300 (−1.9%) | August 31, 2026 |
| 8 | Fidelity Growth Company K6 | 0.79% | 407K | $3.4M | −8,100 (−2.0%) | August 31, 2026 |
| 9 | Federated Hermes MDT Small Cap Core IS | 0.77% | 394K | $3.3M | — | June 30, 2026 |
| 10 | iShares Biotechnology ETF | 0.68% | 350K | $2.9M | −2,648 (−0.8%) | September 30, 2026 |
| 11 | Vanguard Strategic Small-Cap Equity Inv | 0.65% | 333K | $2.8M | — | June 30, 2026 |
| 12 | BlackRock Advantage Small Cap Core Instl | 0.58% | 300K | $2.5M | +5,779 (+2.0%) | August 31, 2026 |
| 13 | Vanguard Russell 2000 ETF | 0.49% | 252K | $2.1M | −3,600 (−1.4%) | September 30, 2026 |
| 14 | DFA US Small Cap I | 0.47% | 242K | $2.0M | — | August 31, 2026 |
| 15 | iShares Russell 2000 Growth ETF | 0.46% | 237K | $2.0M | −300 (−0.1%) | September 30, 2026 |
| 16 | Bridge Builder Small/Mid Cap Value | 0.43% | 218K | $1.8M | +199,549 (+1,057.5%) | September 30, 2026 |
| 17 | Schwab US Small-Cap ETF™ | 0.42% | 214K | $1.8M | +144 (+0.1%) | September 30, 2026 |
| 18 | Federated Hermes MDT Small Cap Core ETF | 0.40% | 204K | $1.7M | −1,701 (−0.8%) | September 30, 2026 |
| 19 | Fidelity Extended Market Index | 0.39% | 200K | $1.7M | +52,907 (+35.8%) | August 31, 2026 |
| 20 | Canada Life US Small-Mid Cap Growth F | 0.34% | 175K | $1.5M | — | July 31, 2026 |
Funds report holdings monthly or quarterly; dates differ by fund.
PRTA insider transactions
latest 20| Date | Name | Transaction | Price | Shares | Value |
|---|---|---|---|---|---|
| 2025-01-14 | William P Scully | Buy | $12.79 | 100,000 | $1.3M |
| 2024-12-31 | William P Scully | Buy | $13.01 | 32,000 | $416,320 |
| 2024-12-20 | William P Scully | Buy | $15.91 | 2,000 | $31,820 |
| 2024-12-18 | William P Scully | Buy | $13.93 | 73,436 | $1.0M |
| 2024-01-24 | Karin L. Walker | Sell | $34.00 | 5,000 | $170,000 |
| 2023-12-20 | Karin L. Walker | Sell | $37.19 | 5,000 | $185,950 |
| 2023-11-30 | Karin L. Walker | Sell | $34.00 | 5,000 | $170,000 |
| 2023-10-25 | Karin L. Walker | Sell | $41.04 | 5,000 | $205,200 |
| 2023-10-11 | Brandon S. Smith | Sell | $46.75 | 4,000 | $187,000 |
| 2023-10-04 | Carol D. Karp | Sell | $46.62 | 5,000 | $233,100 |
| 2023-09-27 | Michael J. Malecek | Sell | $47.38 | 5,000 | $236,900 |
| 2023-09-19 | Karin L. Walker | Sell | $52.36 | 5,000 | $261,800 |
| 2023-09-13 | Brandon S. Smith | Sell | $55.49 | 4,000 | $221,960 |
| 2023-09-13 | Hideki Garren | Sell | $55.48 | 2,000 | $110,960 |
| 2023-09-06 | Carol D. Karp | Sell | $54.76 | 5,000 | $273,800 |
| 2023-08-30 | Michael J. Malecek | Sell | $55.01 | 5,000 | $275,050 |
| 2023-08-18 | Karin L. Walker | Sell | $57.18 | 5,000 | $285,900 |
| 2023-08-16 | Hideki Garren | Sell | $58.74 | 2,000 | $117,480 |
| 2023-08-16 | Brandon S. Smith | Sell | $58.71 | 4,000 | $234,840 |
| 2023-08-02 | Wagner M. Zago | Sell | $67.05 | 4,000 | $268,200 |
Reported trades by company officers, directors and other filers (including disclosures by members of Congress where EODHD lists them). "—" where the filing gives no share count.
PRTA shares outstanding
Year-end shares outstanding, adjusted for splits.
Who owns PRTA
Institutional investors own 93.2% of Prothena's shares and insiders 22.56%. The largest holder is FMR Inc with 14.02% of the shares (7.2M), as of June 30, 2026. Among the top 20 institutions, 13 added shares and 6 reduced their stake in the latest filings. Short interest is 18.79% of the float, or 17.58 days of average trading volume. The share count rose 96.6% since 2014.
Related: PRTA analyst forecast, PRTA key metrics. See the PRTA stock overview for the latest quote and news.
PRTA ownership FAQ
Who owns the most Prothena stock?
The largest shareholders of Prothena are FMR Inc (14.02%), Rubric Capital Management LP (9.74%), BlackRock Inc (9.48%), State Street Corp (4.66%), Acadian Asset Management LLC (3.92%).
What percentage of Prothena is owned by institutions?
Institutions hold 93.2% of Prothena's shares outstanding; insiders hold 22.56%.
Which funds own Prothena?
The largest fund holders of Prothena are Fidelity Growth Company Fund (4.26%), iShares Russell 2000 ETF (2.18%), State Street® SPDR® S&P® Biotech ETF (1.77%), Vanguard Explorer Inv (1.48%), Fidelity Series Growth Company (1.41%).
What is Prothena's short interest?
8.0M shares of Prothena were sold short, 18.79% of the float; at the average daily volume it would take 17.58 days to cover.
Are insiders buying or selling Prothena?
Of the latest 20 reported insider transactions in Prothena (since August 2, 2023), 4 were purchases and 16 were sales.
How many shares of Prothena are outstanding?
Prothena has 51.3M shares outstanding, of which 34.1M are in the public float.