Prothena

PRTA · NASDAQ

$8.50+$0.02 (+0.24%)TodayMarket closed · Oct 20, 7:30 PM ET

Prev close $8.48

Who owns PRTA

Largest institutional holders, from their latest 13F filings

The 10 largest institutions hold 67.9% of PRTA’s shares.

Fidelity Management & Research Company LLC13.8%
Scully (William P)10.4%
Fennell (Todd W.)9.6%
Rubric Capital Management LP9.6%
Next 6 largest institutions24.7%
All other shareholders32.1%

Top institutional holders of PRTA
Holder	Shares	% of shares	Change, last filing	Filed
Fidelity Management & Research Company LLC	7.20M	13.75%	−352.00K	Jun 30, 2026
Scully (William P)	5.44M	10.40%	+44.00K	Aug 20, 2026
Fennell (Todd W.)	5.01M	9.57%	+515.00K	Jun 30, 2026
Rubric Capital Management LP	5.00M	9.55%	+0	Jun 30, 2026
BlackRock Institutional Trust Company, N.A.	3.68M	7.04%	+135.10K	Jun 30, 2026
State Street Investment Management (US)	2.39M	4.57%	+454.93K	Jun 30, 2026
Acadian Asset Management LLC	2.01M	3.84%	+463.05K	Jun 30, 2026
Vanguard Portfolio Management, LLC	1.65M	3.15%	+205.31K	Jun 30, 2026
D. E. Shaw & Co., L.P.	1.61M	3.08%	−151.89K	Jun 30, 2026
Adar1 Capital Management LLC	1.55M	2.97%	−26.91K	Jun 30, 2026

Largest mutual fund holders

Top mutual fund holders of PRTA
Holder	Shares	% of shares	Change, last filing	Filed
Fidelity Growth Company Fund	2.23M	4.26%	+0	Jul 31, 2026
State Street SPDR S&P Biotech ETF	1.53M	2.93%	+102.91K	Aug 31, 2026
iShares Russell 2000 ETF	1.16M	2.21%	−5.06K	Jul 31, 2026
Vanguard Explorer Fund	757.20K	1.45%	+139.98K	Jun 30, 2026
Fidelity Series Growth Company Fund	738.00K	1.41%	+0	Jul 31, 2026

Insider trades

Form 4 filings by officers, directors and large holders

Over the last 6 months, insiders bought $9.45M (16 trades) and sold $135.97K (2 trades) of PRTA on the open market.

Latest PRTA insider transactions
Insider	Date	Type	Shares	Price	Value
SCULLY WILLIAM P	Oct 14, 2026	Buy	10.00K	$8.46	$84.57K
SCULLY WILLIAM P	Oct 13, 2026	Buy	100.00K	$8.35	$835.48K
SCULLY WILLIAM P	Oct 8, 2026	Buy	90.00K	$8.57	$770.90K
SCULLY WILLIAM P	Oct 7, 2026	Buy	125.00K	$8.40	$1.05M
SCULLY WILLIAM P	Oct 2, 2026	Buy	100.00K	$8.57	$857.24K
SCULLY WILLIAM P	Sep 28, 2026	Buy	103.50K	$8.60	$889.87K
SCULLY WILLIAM P	Sep 18, 2026	Buy	100.00K	$8.43	$843.46K
SCULLY WILLIAM P	Sep 2, 2026	Buy	27.00K	$9.47	$255.74K
SCULLY WILLIAM P	Aug 20, 2026	Buy	50.00K	$8.79	$439.43K
SCULLY WILLIAM P	Aug 18, 2026	Gift	627.55K	—	—

Short interest

Settled Sep 30, 2026

Shares short: 8.01M
Days to cover: 13.79
% of shares outstanding: 15.30%
Average daily volume: 580.88K
Change since last report: −6.2%

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