SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* Mirabelli Christopher (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC, 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol PROTEOSTASIS THERAPEUTICS, INC. [ PTI ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 02/17/2016
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X 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. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction 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	02/17/2016		C		1,774,295(1)	A	(1)	1,774,295	I	See Footnote(2)
Common Stock	02/17/2016		P		375,000(3)	A	$8	2,149,295	I	See Footnote(2)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction 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 (Month/Day/Year)		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: 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
Series A Convertible Redeemable Preferred Stock	(4)	02/17/2016		C			11,600,000	(4)	(4)	Common Stock	1,559,707(5)	$0.00	0	I	See Footnote(2)
Series B Convertible Redeemable Preferred Stock	(4)	02/17/2016		C			2,319,750	(4)	(4)	Common Stock	214,588	$0.00	0	I	See Footnote(2)
Series A Convertible Preferred Warrant (Right to Buy)	$1	02/17/2016		J(6)			160,000	07/08/2008	07/08/2018	Series A Preferred Stock	160,000	$0.00	0	I	See Footnote(2)
Common Stock Warrant (Right to Buy)	$10.8102	02/17/2016		J(6)		14,800		07/08/2008	07/08/2018	Common Stock	14,800	$0.00	14,800	I	See Footnote(2)

1. Name and Address of Reporting Person* Mirabelli Christopher (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC, 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer X Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* HealthCare Ventures VIII, L.P. (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC, 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* CAVANAUGH JAMES H (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* HealthCare Partners VIII, LLC (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* HealthCare Partners VIII, L.P. (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* LAWLOR AUGUSTINE (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* LITTLECHILD JOHN W (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* WERNER HAROLD R (Last) (First) (Middle) C/O HEALTHCARE VENTURES LLC 47 THORNDIKE STREET, SUITE B1-1 (Street) CAMBRIDGE MA 02141 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. This transaction represents the total number of shares of Common Stock of the Issuer (the "Issuer Common Stock") received upon the conversion of the Issuer's Series A Convertible Redeemable Preferred Stock (the "Series A Shares"), the payment of accrued dividends on the Series A Shares and the conversion of the Issuer's Series B Convertible Redeemable Preferred Stock ( collectively, the "Preferred Shares").

2. The securities are held of record by HealthCare Ventures VIII, L.P. ("HCVVIII"). HealthCare Partners VIII, L.P. ("HCPVIII") is the General Partner of HCVVIII and HealthCare Partners VIII, LLC (the "LLC") is the General Partner of HCPVIII. Each of James Cavanaugh, Harold Werner, John Littlechild, Christopher Mirabelli and Augustine Lawlor are the managing directors of the LLC and exercise shared voting and investment power with respect to the shares owned by HCVVIII. Each of the reporting persons disclaims beneficial ownership of such securities, except to the extent of his, her or its proportionate pecuniary interest therein. Dr. Mirabelli is also a director of the issuer.

3. These securities were purchased in the initial public offering of the Issuer.

4. The Preferred Shares automatically converted into Issuer Common Stock on a 10.8102-to-1 basis upon the closing of the initial public offering of the Issuer without payment or further consideration. The Preferred Shares were convertible at any time at the election of the Reporting Person and had no expiration date.

5. These securities include shares of Issuer Common Stock received as payment for accrued dividends on the Series A Shares.

6. This transaction represents a deemed disposition of warrants to purchase Series A Shares and a deemed acquisition of warrants to purchase shares of Issuer Common Stock on a 10.8102-to-1 basis, which occurred automatically upon the closing of the initial public offering of the Issuer without payment or further consideration. The transaction is listed solely for the purpose of reporting the change in the shares underlying the warrants.

Remarks:

	/s/ Jeffrey B. Steinberg, Attorney-in-Fact for Christopher Mirabelli	02/17/2016
	/s/ Jeffrey B. Steinberg, Administrative Partner of HealthCare Ventures VII, L.P.	02/17/2016
	/s/ Jeffrey B. Steinberg, Attorney-in-Fact for James H. Cavanaugh	02/17/2016
	/s/ Jeffrey B. Steinberg, Administrative Officer of HealthCare Partners VIII LLC	02/17/2016
	/s/ Jeffrey B. Steinberg, Administrative Partner of HealthCare Partners VIII, L.P.	02/17/2016
	/s/ Jeffrey B. Steinberg, Attorney-in-Fact for Augustine Lawlor	02/17/2016
	/s/ Jeffrey B. Steinberg, Attorney-in-Fact for John Littlechild	02/17/2016
	/s/ Jeffrey B. Steinberg, Attorney-in-Fact for Harold Werner	02/17/2016
	** Signature of Reporting Person	Date
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