Leerink Partners LLC and RBC Capital Markets, LLC are acting as joint book-running managers for the offering. H.C. Wainwright & Co., LLC is acting as lead manager for the offering. The securities described above are being offered by Proteostasis pursuant to a shelf registration statement (File No. 333-218545), which was declared effective by the Securities and Exchange Commission (SEC) on July 3, 2017. The securities may be offered only by means of a prospectus.