6CJC:
reference: Antigen-Induced Allosteric Changes in a Human IgG1 Fc Increase Low-Affinity Fcgamma Receptor Binding., Orlandi C, Deredge D, Ray K, Gohain N, Tolbert W, DeVico AL, Wintrode P, Pazgier M, Lewis GK, Structure. 2020 May 5;28(5):516-527.e5. doi: 10.1016/j.str.2020.03.001. Epub 2020, Mar 24. PMID: 32209433

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