X0306 4 2016-02-17 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001273885 BERGER FRANKLIN M 200 TECHNOLOGY SQUARE, 4TH FLOOR CAMBRIDGE MA 02139 1 0 0 0 Common Stock 2016-02-17 4 C 0 71932 A 71932 D Common Stock 2016-02-17 4 P 0 25000 8.00 A 96932 D Series B Convertible Redeemable Preferred Stock 2016-02-17 4 C 0 777604 D Common Stock 71932 0 D This transaction represents the total number of shares of Issuer Common Stock received upon the conversion of the Issuer's Series B Convertible Redeemable Preferred Stock (the "Series B Shares"). These securities were purchased in the initial public offering of the Issuer. The Series B Shares automatically converted into Issuer Common Stock on a 10.8102-to-1 basis upon the closing of the initial public offering of the Issuer without payment or further consideration. The Series B Shares were convertible at any time at the election of the Reporting Person and had no expiration date. /s/ Janet L. Smart, Attorney-in-Fact 2016-02-17