X0306 4 2016-02-10 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001661335 Lee Po Shun 200 TECHNOLOGY SQUARE, 4TH FLOOR CAMBRIDGE MA 02139 0 1 0 0 See Remarks Employee Stock Option (Right to Buy) 8.00 2016-02-10 4 A 0 99926 0.00 A 2026-02-10 Common Stock 99926 99926 D These securities shall vest and become exercisable in a series of installments, with the first installment to become exercisable for 25% of the underlying common stock on February 10, 2017, and thereafter vesting and becoming exercisable in quarterly installments as nearly equal as practicable (as determined by the Issuer in its reasonable discretion), until such stock option becomes fully exercisable on February 10, 2020, provided that the Reporting Person remains an employee of Issuer at all times during the applicable vesting period of such securities. Executive Vice President and Chief Medical Officer /s/ Janet L. Smart, Attorney-in-Fact 2016-02-12