X0306 4 2016-02-10 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001661484 Walshe Conor M 200 TECHNOLOGY SQUARE, 4TH FLOOR CAMBRIDGE MA 02139 1 0 0 0 Stock Option (Right to Buy) 8.00 2016-02-10 4 A 0 45760 0.00 A 2026-02-10 Common Stock 45760 45760 D These securities shall vest and become exercisable in equal quarterly installments starting on February 10, 2016 until the option is fully vested and exercisable on February 10, 2019, subject to continued service. The Reporting Person is an employee of an affiliate of Perrigo Company plc ("Perrigo"), the indirect parent of Elan Science One Ltd. Perrigo may be deemed to beneficially own the 45,760 options granted to Mr. Walshe in his capacity as a director of the Company. Mr. Walshe has an understanding with Perrigo pursuant to which he holds such securities for the benefit of Perrigo. The Reporting Person disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that the Reporting Person is the beneficial owner of, or has any pecuniary interest in, such securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose. /s/ Janet L. Smart, Attorney-in-Fact 2016-02-12