X0306 4 2018-10-01 1 0001382101 SUTRO BIOPHARMA INC STRO 0001399763 Alta Partners VIII, L.P. ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO CA 94111 0 0 1 0 0001399894 Alta Partners Management VIII, LLC ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO CA 94111 0 0 1 0 0001198321 CHAMPSI FARAH ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO CA 94111 0 0 1 0 0001198325 JANNEY DANIEL ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO CA 94111 1 0 1 0 0001198330 NOHRA GUY P ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO CA 94111 0 0 1 0 Common Stock 2018-10-01 4 C 0 589661 A 589661 D Common Stock 2018-10-01 4 C 0 458331 A 1047992 D Common Stock 2018-10-01 4 C 0 382698 A 1430690 D Common Stock 2018-10-01 4 C 0 514211 A 1944901 D Series B Preferred Stock 2018-10-01 4 C 0 10201769 0.00 D Common Stock 589661 0 D Series C Preferred Stock 2018-10-01 4 C 0 12387324 0.00 D Common Stock 458331 0 D Series D Preferred Stock 2018-10-01 4 C 0 9449318 0.00 D Common Stock 382698 0 D Series E Preferred Stock 2018-10-01 4 C 0 18698578 0.00 D Common Stock 514211 0 D Each share of the issuer's Series B Preferred Stock automatically converted into 0.0578 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its firm commitment initial public offering (the "IPO") pursuant to a registration statement on Form S-1 (File No. 333-227103) under the Securities Act of 1933, as amended (the "Registration Statement"), and had no expiration date. The shares directly held by Alta Partners VIII, L.P. ("Alta VIII") are indirectly held by Alta Partners Management VIII, LLC ("Alta Management VIII"), which is the general partner of Alta VIII. The individual managing directors of Alta Management VIII are Farah Champsi, Guy Nohra and Daniel Janney. The managing directors of Alta Management VIII exercise sole voting and investment control with respect to the shares held by Alta VIII. The individual managing directors of Alta Management VIII disclaim beneficial ownership of all shares held by Alta VIII, except to the extent of their pecuniary interests therein. Each share of the issuer's Series C Preferred Stock automatically converted into 0.0370 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. Each share of the issuer's Series D Preferred Stock automatically converted into 0.0405 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. Each share of the issuer's Series E Preferred Stock automatically converted into 0.0275 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC, the general partner of Alta Partners VIII, L.P. 2018-10-01 /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC 2018-10-01 /s/ Farah Champsi 2018-10-01 /s/ Daniel Janney 2018-10-01 /s/ Guy Nohra 2018-10-01