SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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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. Date of Event Requiring Statement (Month/Day/Year) 02/10/2016	3. Issuer Name and Ticker or Trading Symbol PROTEOSTASIS THERAPEUTICS, INC. [ PTI ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director X 10% Owner Officer (give title below) Other (specify below)	5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A Convertible Redeemable Preferred Stock	(1)	(1)	Common Stock	1,559,707(1)	(1)	I	See Footnote(2)
Series A Convertible Redeemable Pref. Warrant (Right to Buy)	07/08/2008	07/08/2018	Series A Convertible Redeemable Preferred Stock	160,000(3)	$1(3)	I	See Footnote(2)
Series B Convertible Redeemable Preferred Stock	(4)	(4)	Common Stock	214,588(4)	(4)	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. The Series A Convertible Redeemable Preferred Stock (the "Series A Shares") are convertible on a 10.8102-to-1 basis into the Issuer's Common Stock at any time at the election of the Reporting Person and will automatically convert, together with the accrued but unpaid dividends, upon the closing of the Issuer's initial public offering into the number of shares of the Issuer's Common Stock shown in column 3. The Series A Shares do not have an expiration date.

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 are exercisable for Series A Shares at such exercise price per share as listed in columns 3 and 4. Upon the closing of the Issuer's initial public offering, the Warrant will automatically become exercisable for 14,800 shares of Common Stock at an exercise price of $10.8102 per share.

4. The Series B Convertible Redeemable Preferred Stock (the "Series B Shares") are convertible on a 10.8102-to-1 basis into the number of shares of the Issuer's Common Stock as shown in column 3 at any time at the election of the Reporting Person and will automatically convert upon the closing of the Issuer's initial public offering. The Series B Shares do not have an expiration date.

Remarks:

	Jeffrey B. Steinberg, Attorney-in-Fact for Christopher Mirabelli	02/10/2016
	Jeffrey B. Steinberg, Administrative Partner of HealthCare Ventures VII, L.P.	02/10/2016
	Jeffrey B. Steinberg, Attorney-in-Fact for James H. Cavanaugh	02/10/2016
	Jeffrey B. Steinberg, Administrative Officer of HealthCare Partners VIII LLC	02/10/2016
	Jeffrey B. Steinberg, Administrative Partner of HealthCare Partners VIII, L.P.	02/10/2016
	Jeffrey B. Steinberg, Attorney-in-Fact for Augustine Lawlor	02/10/2016
	Jeffrey B. Steinberg, Attorney-in-Fact for John Littlechild	02/10/2016
	Jeffrey B. Steinberg, Attorney-in-Fact for Harold Werner	02/10/2016
	** 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 5 (b)(v).
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