X0306 4 2018-06-21 0 0001559053 Prothena Corp plc PRTA 0001457013 Nguyen Tran C/O PROTHENA BIOSCIENCES INC 331 OYSTER POINT BOULEVARD SOUTH SAN FRANCISCO CA 94080 0 1 0 0 COO and CFO Ordinary Shares, par value $0.01 per share 3200 D Stock Option (right to buy) 15.04 2018-06-21 4 A 0 250000 0.00 A 2028-06-21 Ordinary Shares 250000 250000 D The shares subject to the option will vest and become exercisable as to 25% of the total number of shares subject to the option on June 21, 2019 and with respect to 1/48th of the total number of shares subject to the option in successive, equal monthly installments on each monthly anniversary thereafter, subject to the Reporting Person's continued employment with the Issuer on each such vesting date. /s/ A.W. Homan, as Attorney-in-Fact for Tran B. Nguyen 2018-06-25