X0306 4 2016-02-17 1 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001297709 Novartis Bioventures Ltd 131 FRONT STREET HAMILTON D0 HM12 BERMUDA 0 0 1 0 0001114448 NOVARTIS AG LICHTSTRASSE 35 BASEL V8 4056 SWITZERLAND 0 0 1 0 Common Stock 2016-02-17 4 C 0 1498791 A 1498791 D Common Stock 2016-02-17 4 P 0 375000 8.00 A 1873791 D Series A Convertible Redeemable Preferred Stock 2016-02-17 4 C 0 10000000 0.00 D Common Stock 1318932 0 D Series B Convertible Redeemable Preferred Stock 2016-02-17 4 C 0 1944315 0.00 D Common Stock 179859 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 (the "Series B Shares", collectively, the "Preferred Shares"). These securities are held directly by Novartis Bioventures Ltd. ("Novartis Bioventures"). Novartis Bioventures is a corporation organized under the laws of Bermuda and is an indirect wholly-owned subsidiary of Novartis AG. Novartis AG is a corporation organized under the laws of Switzerland and is the publicly owned parent of Novartis Bioventures Ltd. These securities were purchased in connection with 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. NOVARTIS BIOVENTURES LTD., /s/ Simon Zivi, Chairman 2016-02-17 NOVARTIS BIOVENTURES LTD., /s/ Laurieann Chaikowsky, Authorized Signatory 2016-02-17 NOVARTIS AG, /s/ Simon Zivi, Authorized Signatory 2016-02-17 NOVARTIS AG, /s/ Laurieann Chaikowsky, Authorized Signatory 2016-02-17