X0206 3 2016-02-10 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0001262326 Mirabelli Christopher C/O HEALTHCARE VENTURES LLC, 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 1 0 1 0 0001358990 HealthCare Ventures VIII, L.P. C/O HEALTHCARE VENTURES LLC, 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001013473 CAVANAUGH JAMES H C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001358992 HealthCare Partners VIII, LLC C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001358991 HealthCare Partners VIII, L.P. C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001262327 LAWLOR AUGUSTINE C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001013469 LITTLECHILD JOHN W C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 0001013603 WERNER HAROLD R C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 CAMBRIDGE MA 02141 0 0 1 0 Series A Convertible Redeemable Preferred Stock Common Stock 1559707 I See Footnote Series A Convertible Redeemable Pref. Warrant (Right to Buy) 1.00 2008-07-08 2018-07-08 Series A Convertible Redeemable Preferred Stock 160000 I See Footnote Series B Convertible Redeemable Preferred Stock Common Stock 214588 I See Footnote 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. The securities are held of record by HealthCare Ventures VIII, L.P. ("HCVVIII"). HealthCare Partners VIII, L.P. ("HCPVIII") is the General Partner of HCVVIII and HealthCare Partners VIII, LLC (the "LLC") is the General Partner of HCPVIII. Each of James Cavanaugh, Harold Werner, John Littlechild, Christopher Mirabelli and Augustine Lawlor are the managing directors of the LLC and exercise shared voting and investment power with respect to the shares owned by HCVVIII. Each of the reporting persons disclaims beneficial ownership of such securities, except to the extent of his, her or its proportionate pecuniary interest therein. Dr. Mirabelli is also a director of the issuer. These securities are exercisable for Series A Shares at such exercise price per share as listed in columns 3 and 4. Upon the closing of the Issuer's initial public offering, the Warrant will automatically become exercisable for 14,800 shares of Common Stock at an exercise price of $10.8102 per share. 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. Jeffrey B. Steinberg, Attorney-in-Fact for Christopher Mirabelli 2016-02-10 Jeffrey B. Steinberg, Administrative Partner of HealthCare Ventures VII, L.P. 2016-02-10 Jeffrey B. Steinberg, Attorney-in-Fact for James H. Cavanaugh 2016-02-10 Jeffrey B. Steinberg, Administrative Officer of HealthCare Partners VIII LLC 2016-02-10 Jeffrey B. Steinberg, Administrative Partner of HealthCare Partners VIII, L.P. 2016-02-10 Jeffrey B. Steinberg, Attorney-in-Fact for Augustine Lawlor 2016-02-10 Jeffrey B. Steinberg, Attorney-in-Fact for John Littlechild 2016-02-10 Jeffrey B. Steinberg, Attorney-in-Fact for Harold Werner 2016-02-10