FORM 4
[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

1. Name and Address of Reporting Person *

FMR LLC 		2. Issuer Name and Ticker or Trading Symbol

PROTEOSTASIS THERAPEUTICS, INC. [ PTI ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                      __ X __ 10% Owner
_____ Officer (give title below)      __ X __ Other (specify below)
See Remark 1
(Last)          (First)          (Middle)

245 SUMMER STREET 		3. Date of Earliest Transaction (MM/DD/YYYY)

3/10/2017
(Street)

BOSTON, MA 02210
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
6. Individual or Joint/Group Filing (Check Applicable Line)

_ X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8) 		4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4) 		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock   3/10/2017     S    25000   D $12.04   (2) 268508   I   See footnote   (1)

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3) 		2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8) 		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4) 		8. Price of Derivative Security
(Instr. 5) 		9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Explanation of Responses:
( 1)  By Impresa Fund III Limited Partnership (263,685 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.
( 2)  The price reported for this transaction is the weighted average price of multiple trades at prices ranging from $11.83 to $12.36. 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.

Remarks:
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.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
FMR LLC
245 SUMMER STREET
BOSTON, MA 02210
X
See Remark 1

Signatures
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 3/13/2017
** Signature of Reporting Person Date


Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.
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