Exhibit 32.1

Certification Pursuant to

18 U.S.C. Section 1350

as Adopted Pursuant to

Section 906 of the Sarbanes-Oxley Act of 2002

In connection with the Annual Report on Form 10-K of Proteostasis Therapeutics, Inc. (the “Company”) for the year ended December 31, 2018, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned officer hereby certifies, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, that to the best of my knowledge:  

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: March 8, 2019	/s/ Meenu Chhabra
	Meenu Chhabra
	President and Chief Executive Officer (Principal Executive Officer)

In connection with the Annual Report on Form 10-K of Proteostasis Therapeutics, Inc. (the “Company”) for the year ended December 31, 2018, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned officer hereby certifies, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, that to the best of my knowledge:  

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: March 8, 2019	/s/ Sandra Zimmerman
	Sandra Zimmerman
	Interim Vice President of Finance (Principal Financial and Accounting Officer)