Exhibit 1

JOINT FILING AGREEMENT

This Joint Filing Agreement, dated as of February 26, 2016, is by and among Cormorant Global Healthcare Master Fund, LP, Cormorant Global Healthcare GP, LLC, Cormorant Asset Management, LLC and Bihua Chen (collectively, the “Filers”).

Each of the Filers may be required to file with the United States Securities and Exchange Commission a statement on Schedule 13D and/or 13G with respect to shares of Common Stock of Proteostasis Therapeutics, Inc. beneficially owned by them from time to time.

Pursuant to and in accordance with Rule 13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to file a single statement on Schedule 13D and/or 13G (and any amendments thereto) on behalf of each of the Filers, and hereby further agree to file this Joint Filing Agreement as an exhibit to such statement, as required by such rule.

This Joint Filing Agreement may be terminated by any of the Filers upon written notice or such lesser period of notice as the Filers may mutually agree.

Executed and delivered as of the date first above written.

CORMORANT GLOBAL HEALTHCARE MASTER FUND, LP

By: Cormorant Global Healthcare GP, LLC

its General Partner

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT GLOBAL HEALTHCARE GP, LLC

By: /s/ Bihua Chen

Bihua Chen, Managing Member

CORMORANT ASSET MANAGEMENT, LLC

By: /s/ Bihua Chen

Bihua Chen, Managing Member

/s/ Bihua Chen

Bihua Chen