6B9Y:
reference: Template-Catalyzed, Disulfide Conjugation of Monoclonal Antibodies Using a Natural Amino Acid Tag., King JD, Ma Y, Kuo YC, Bzymek KP, Goodstein LH, Meyer K, Moore RE, Crow D, Colcher DM, Singh G, Horne DA, Williams JC, Bioconjug Chem. 2018 Jun 20;29(6):2074-2081. doi:, 10.1021/acs.bioconjchem.8b00284. Epub 2018 May 25. PMID: 29763554

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).