Form DEFA14A Protagonist Therapeutics

Your Vote Counts! PROTAGONIST THERAPEUTICS, INC. 2023 Annual Meeting Vote by May 24, 2023 11:59 PM ET You invested in PROTAGONIST THERAPEUTICS, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the stockholder meeting to be held on May 25, 2023. Vote Virtually at the Meeting* May 25, 2023 10:00 AM PDT *Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number For complete information and to vote, visit www.ProxyVote.com Control # V09872-P91323 Get informed before you vote View the Notice and Proxy Statement and Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 11, 2023. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to [email protected]. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. PROTAGONIST THERAPEUTICS, INC. 7707 GATEWAY BLVD. SUITE 140 NEWARK, CA 94560 Vote Virtually at the Meeting: To vote during the Meeting go to www.virtualshareholdermeeting.com/PTGX2023. Have the control number that is printed in the box available and follow the instructions. Vote Before the Meeting by Internet: To vote now by internet, go to www.proxyvote.com. Have the control number that is printed in the box available and follow the instructions. Vote Before the Meeting by Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card. V1.2

THIS IS NOT A VOTABLE BALLOT This is an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials at www.proxyvote.com or easily request a paper copy. We encourage you to access and review all of the important information contained in the proxy materials before voting. Please follow the instructions on the reverse side to vote these important matters. Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”. Voting Items Board Recommends V09873-P91323 01) Dinesh V. Patel, Ph.D. 1. To elect the Class I director nominee named below to serve until the 2026 Annual Meeting of Stockholders and until his successor has been duly elected and qualified. Nominee: 2. To approve, on an advisory basis, the compensation of our named executive officers. 3. To ratify the selection by the Audit Committee of the Board of Ernst & Young LLP as Protagonist Therapeutics’ independent registered public accounting firm for the fiscal year ending December 31, 2023. NOTE: The Board of Directors knows of no other matters that will be presented for consideration at the 2023 Annual Meeting of Stockholders. If any other matters are properly brought before the 2023 Annual Meeting of Stockholders or any postponement or adjournment thereof, it is the intention of the proxies named in the proxy card to vote on such matters in accordance with their best judgment. For For For