X0306 4 2016-02-17 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001383391 New Enterprise Associates 12, Limited Partnership 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001383390 NEA Partners 12, Limited Partnership 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001383389 NEA 12 GP, LLC 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001005561 BARRIS PETER J 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001277631 BASKETT FOREST 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001235112 KERINS PATRICK J 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001270521 KOLLURI KRISHNA KITTU 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001237289 SANDELL SCOTT D 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 Common Stock 2016-02-17 4 C 0 2192748 A 2192748 D Common Stock 2016-02-17 4 P 0 900324 8.00 A 3093072 D Series A Convertible Redeemable Preferred Stock 2016-02-17 4 C 0 13848000 0.00 D Common Stock 1783531 0 D Series B Convertible Redeemable Preferred Stock 2016-02-17 4 C 0 4423723 0.00 D Common Stock 409217 0 D This transaction represents the total number of shares of Common Stock of the Issuer (the "Issuer Common Stock") received upon the conversion of the Issuer's Series A Convertible Redeemable Preferred Stock (the "Series A Shares"), the payment of accrued dividends on the Series A Shares and the conversion of the Issuer's Series B Convertible Redeemable Preferred Stock ( collectively, the "Preferred Shares"). The shares are directly held by New Enterprise Associates 12, Limited Partnership ("NEA 12") and indirectly held by NEA Partners 12, Limited Partnership ("NEA Partners 12"), the sole general partner of NEA 12, NEA 12 GP, LLC ("NEA 12 GP"), the sole general partner of NEA Partners 12, and the individual managers of NEA 12 GP (NEA Partners 12, NEA 12 GP and the individual managers of NEA 12 GP together, the "NEA 12 Indirect Reporting Persons"). The individual managers of NEA 12 GP are M. James Barrett, Peter J. Barris, Forest Baskett, Patrick J. Kerins, Krishna "Kittu" Kolluri, and Scott D. Sandell. The NEA 12 Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the NEA 12 shares in which the NEA 12 Indirect Reporting Persons have no pecuniary interest. These securities were purchased in the initial public offering of the Issuer. The Preferred 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 Preferred Shares were convertible at any time at the election of the Reporting Person and had no expiration date. These securities include shares of Issuer Common Stock received as payment for accrued dividends on the Series A Shares. /s/ Sasha Keough, attorney-in-fact 2016-02-17