Prothena Corporation plc
Feb 3, 2014

Prothena Announces Closing of Underwritten Public Offering of Ordinary Shares and Full Exercise of Underwriters' Option to Purchase Additional Ordinary Shares From Perrigo

DUBLIN, Ireland, Feb. 3, 2014 (GLOBE NEWSWIRE) -- Prothena Corporation plc (Nasdaq:PRTA), a clinical stage biotechnology company focused on the discovery, development and commercialization of novel antibodies for the potential treatment of diseases that involve protein misfolding and cell adhesion, announced today the closing of a previously announced underwritten public offering of its ordinary shares owned by Elan Science One Limited (the "Selling Shareholder"), an indirect wholly owned subsidiary of Perrigo Company plc ("Perrigo"). The offering of 3,182,253 ordinary shares of Prothena included 415,076 ordinary shares that were sold pursuant to the underwriters' option to purchase additional shares, which was exercised in full prior to closing. The ordinary shares were sold at a price to the public of $26.00 per ordinary share, before the underwriting discount. As a result of the full exercise of the underwriters' option, the Selling Shareholder and Perrigo no longer own any ordinary shares of Prothena.

All of the ordinary shares in the offering, including the shares subject to the underwriters' option, were sold by the Selling Shareholder. Prothena did not receive any of the proceeds from the offering, and the total number of Prothena ordinary shares outstanding did not change as a result of the offering.

BofA Merrill Lynch and Citigroup acted as joint book-running managers for the offering.

A registration statement on Form S-3 relating to the ordinary shares was filed with the Securities and Exchange Commission and declared effective. The offering of these securities was made only by means of a written prospectus supplement and base prospectus forming part of the effective registration statement relating to the ordinary shares. Copies of the prospectus for this offering may be obtained by contacting BofA Merrill Lynch, 222 Broadway, New York, NY 10038, Attn: Prospectus Department, email: dg.prospectus_requests@baml.com, or Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, via telephone at 1-800-831-9146 or email at batprospectusdept@citi.com.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state or other jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or other jurisdiction.

CONTACT: Investors: Tran Nguyen, CFO

         650-837-8535, IR@prothena.com

         Media: Anita Kawatra

         646-256-5116, anita.kawatra@prothena.com