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Table of Contents 冈 ☐ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission File No. 001-37852 to PROTAGONIST THERAPEUTICS , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 7707 Gateway Boulevard , Suite 140 Newark , California 94560 ( Address , including zip code , of registrant's principal executive offices ) 98-0505495 ( I.R.S. Employer Identification No. ) ( 510 ) 474-0170 ( Telephone number , including area code , of registrant's principal executive offices ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock , $ 0.00001 par value Trading Symbol PTGX Securities registered pursuant to Section 12 ( g ) of the Act : None Name of each exchange on which registered The Nasdaq Global Market No □ Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes ☑ Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes □ No ☑ Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes ☑No □ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( $ 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No □ Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of “ large accelerated filer , ” “ accelerated filer , " " smaller reporting company , ” and “ emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer Non - accelerated filer ☐ 図 Accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Yes + No ☐ ☐ ☑ Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . ☐ Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act of 1934 ) . Yes ☐ No ☑ The aggregate market value of the voting stock held by non - affiliates of the registrant was approximately $ 640.7 million as of June 30 , 2020 , based upon the closing sale price on The Nasdaq Global Market reported on June 30 , 2020. Excludes an aggregate of 522,160 shares of the registrant's common stock held by officers , directors and affiliated stockholders . For purposes of determining whether a stockholder was an affiliate of the registrant at June 30 , 2020 , the registrant assumed that a stockholder was an affiliate of the registrant at June 30 , 2020 if such stockholder ( i ) beneficially owned 10 % or more of the registrant's common stock , as determined based on public filings and / or ( ii ) was an executive officer or director or was affiliated with an executive officer or director of the registrant at June 30 , 2020. Exclusion of such shares should not be construed to indicate that any such person possesses the power , direct or indirect , to direct or cause the direction of the management or policies of the registrant or that such person is controlled by or under common control with the registrant . There were 43,808,308 shares of registrant's Common Stock , par value $ 0.00001 per share , outstanding as of February 26 , 2021 . DOCUMENTS INCORPORATED BY REFERENCE : Portions of the registrant's definitive Proxy Statement for the registrant's 2021 Annual Meeting of Stockholders , to be filed subsequent to the date hereof with the Securities and Exchange Commission ( " SEC " ) , are incorporated by reference into Part III of this report . Such proxy statement will be filed with the SEC not later than 120 days after the end of the registrant's fiscal year ended December 31 , 2020 .