X0206 3 2018-09-26 0 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 No securities beneficially held 0 D Series B Preferred Stock Common Stock 10201769 D Series C Preferred Stock Common Stock 12387324 D Series D Preferred Stock Common Stock 9449318 D Series E Preferred Stock Common Stock 18698578 D Series C Preferred Stock Warrant (right to buy) 0.4797 Series C Preferred Stock 671997 D Each share of the issuer's Series B Preferred Stock will automatically convert into 0.0578 share of the issuer's Common Stock immediately upon the closing of the issuer's initial public offering ("IPO") and has 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 will automatically convert into 0.0370 share of the issuer's Common Stock immediately upon the closing of the issuer's IPO and has no expiration date. Each share of the issuer's Series D Preferred Stock will automatically convert into 0.0405 share of the issuer's Common Stock immediately upon the closing of the issuer's IPO and has no expiration date. Each share of the issuer's Series E Preferred Stock will automatically convert into 0.0275 share of the issuer's Common Stock immediately upon the closing of the issuer's IPO and has no expiration date. The warrant is exercisable at any time at the holder's election on a one-for one basis and automatically terminates on the completion of the issuer's initial public offering if not earlier exercised. The warrant has a net exercise provision under which the holder, in lieu of paying the exercise price in cash, can surrender the warrant and receive a net number of shares of preferred stock based on the fair market value of such stock at the time of exercise, after deducting the aggregate exercise price. /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC, the general partner of Alta Partners VIII, L.P. 2018-09-26 /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC 2018-09-26 /s/ Farah Champsi 2018-09-26 /s/ Daniel Janney 2018-09-26 /s/ Guy Nohra 2018-09-26