Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock^F1,F3	Feb 17, 2016	C	2,416,612	—	A	2,416,612	I	See footnote
Common Stock^F2,F3	Feb 17, 2016	C	366,455	—	A	2,783,067	I	See footnote
Common Strock^F4,F3	Feb 17, 2016	P	125,000	$8.00	A	2,908,067	I	See footnote

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	Owned after	D/I
Series A Convertible Redeemable Preferred Stock^F3,F1	—	Feb 17, 2016	C	20,000,000	D	—	—	Common Stock	2,416,612	0	I
Series B Convertible Redeemable Preferred Stock^F3,F2	—	Feb 17, 2016	C	3,961,459	D	—	—	Common Stock	366,455	0	I
Stock Option (Right to Buy)^F6,F5	$8.00	Feb 10, 2016	A	45,760	A	—	Feb 10, 2016	Common Stock	45,760	45,760	I

Explanation of responses

F1The Series A Convertible Redeemable Preferred Stock (the "Series A Shares") automatically converted on a 10.8102-to-1 basis into the Issuer's Common Stock, together with the accrued but unpaid dividends, upon closing of the Issuer's initial public offering into 2,416,612 shares of the Issuer's Common Stock. The Series A Shares did not have an expiration date.
F2The Series B Convertible Redeemable Preferred Stock (the "Series B Shares") automatically converted on a 10.8102-to-1 basis into the Issuer's Common Stock upon closing of the Issuer's initial public offering into 366,455 shares of the Issuer's Common Stock. The Series B Shares did not have an expiration date.
F3Perrigo Science One Ltd. ("Science") (formerly Elan Science One Ltd.) is the direct owner of these securities. Science is a direct or indirect, wholly-owned subsidiary of each of the other reporting persons.
F4These securities were purchased in connection with the initial public offering of the Issuer.
F5These securities shall vest and become exercisable in equal quarterly installments starting on February 10, 2016 until the option is fully vested and exercisable on February 10, 2019, subject to continued service.
F6Perrigo Company plc ("Perrigo") and the other reporting persons named herein may be deemed to beneficially own the 45,760 options granted to Mr. Walshe in his capacity as a director of Proteostasis Therapeutics, Inc. (the "Company"). Mr. Walshe has an understanding with Perrigo pursuant to which he holds such securities for the benefit of Perrigo.