4PCB:
reference: A high security double lock and key mechanism in HUH relaxases controls oriT-processing for plasmid conjugation., Carballeira JD, Gonzalez-Perez B, Moncalian G, la Cruz Fd, Nucleic Acids Res. 2014 Dec 1;42(16):10632-43. doi: 10.1093/nar/gku741. Epub 2014, Aug 14. PMID: 25123661

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