X0206 3 2016-02-10 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001565579 Elan Science One Ltd TREASURY BUILDING, LOWER GRAND CANAL STREET DUBLIN L2 2 IRELAND 0 0 1 0 Series A Convertible Redeemable Preferred Stock Common Stock 2416612 D Series B Convertible Redeemable Preferred Stock Common Stock 366455 D The Series A Convertible Redeemable Preferred Stock (the "Series A Shares") are convertible on a 10.8102-to-1 basis into the Issuer's Common Stock at any time at the election of the Reporting Person and will automatically convert, together with the accrued but unpaid dividends, upon the closing of the Issuer's initial public offering into the number of shares of the Issuer's Common Stock shown in column 3. The Series A Shares do not have an expiration date. lan Science One Ltd. ("Elan") is the direct owner of these securities. Elan is an indirect, wholly-owned subsidiary of Perrigo Company plc and Elan Corporation Limited (formerly Elan Corporation, plc). The Series B Convertible Redeemable Preferred Stock (the "Series B Shares") are convertible on a 10.8102-to-1 basis into the number of shares of the Issuer's Common Stock as shown in column 3 at any time at the election of the Reporting Person and will automatically convert upon the closing of the Issuer's initial public offering. The Series B Shares do not have an expiration date. Exhibit List - Exhibit 24.1 - Power of Attorney /s/ Janet L. Smart, Attorney-in-Fact 2016-02-10