4BX7:
reference: Plug-and-Play Pairing via Defined Divalent Streptavidins., Fairhead M, Krndija D, Lowe ED, Howarth M, J Mol Biol. 2013 Sep 19. pii: S0022-2836(13)00600-1. doi:, 10.1016/j.jmb.2013.09.016. PMID: 24056174

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