6BHQ:
reference: Mouse IgG2c Fc loop residues promote greater receptor-binding affinity than mouse IgG2b or human IgG1., Falconer DJ, Barb AW, PLoS One. 2018 Feb 6;13(2):e0192123. doi: 10.1371/journal.pone.0192123., eCollection 2018. PMID: 29408873

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