X0306 4 2017-02-28 0 0001445283 PROTEOSTASIS THERAPEUTICS, INC. PTI 0000315066 FMR LLC 245 SUMMER STREET BOSTON MA 02210 0 0 1 1 See Remark 1 Common Stock 2017-02-28 4 S 0 15000 14.47 D 457808 I See footnote Common Stock 2017-03-01 4 S 0 30000 14.7 D 427808 I See footnote By Impresa Fund III Limited Partnership (422,985 shares of Common Stock) and F-Prime Inc. (4,823 shares of Common Stock). Impresa Fund III Limited Partnership is solely managed by Impresa Management LLC, its general partner and investment manager. Impresa Management LLC is owned, directly or indirectly, by various shareholders and employees of FMR LLC, including certain members of the Johnson family. F-Prime Inc. is a wholly-owned subsidiary of FMR LLC. The price reported for this transaction is the weighted average price of multiple trades at prices ranging from $14.20 to $14.80. FMR LLC hereby undertakes to provide upon request by the Commission staff, the issuer, or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. The price reported for this transaction is the weighted average price of multiple trades at prices ranging from $14.32 to $14.81. FMR LLC hereby undertakes to provide upon request by the Commission staff, the issuer, or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. Remark 1: Abigail P. Johnson is a Director, the Chairman and the Chief Executive Officer of FMR LLC. Members of the Johnson family, including Abigail P. Johnson, are the predominant owners, directly or through trusts, of Series B voting common shares of FMR LLC, representing 49% of the voting power of FMR LLC. The Johnson family group and all other Series B shareholders have entered into a shareholders' voting agreement under which all Series B voting common shares will be voted in accordance with the majority vote of Series B voting common shares. Accordingly, through their ownership of voting common shares and the execution of the shareholders' voting agreement, members of the Johnson family may be deemed, under the Investment Company Act of 1940, to form a controlling group with respect to FMR LLC. The address of Abigail P. Johnson is c/o FMR LLC, 245 Summer Street, Boston, MA 02110. Remark 2: In addition to the securities shown in Table I, FMR Co., Inc., an indirect wholly-owned subsidiary of FMR LLC and an investment adviser registered under the Investment Advisers Act of 1940, is the beneficial owner of Common Stock of Proteostasis Therapeutics, Inc., as a result of acting as investment adviser to various investment companies registered under the Investment Company Act of 1940. FMR LLC and Abigail P. Johnson have no pecuniary interest in the shares of Common Stock beneficially owned by FMR Co., Inc. Remark 3: The filing of this statement shall not be deemed to be an admission that, for purposes of Section 16 of the Securities Exchange Act of 1934 or otherwise, the undersigned are the beneficial owners of any securities reported herein. Marc R. Bryant, Duly authorized under Powers of Attorney, by and on behalf of FMR LLC and its direct and indirect subsidiaries, and Abigail P. Johnson 2017-03-02