6HBE:
reference: A three-domain copper-nitrite reductase with a unique sensing loop., Opperman DJ, Murgida DH, Dalosto SD, Brondino CD, Ferroni FM, IUCrJ. 2019 Feb 9;6(Pt 2):248-258. doi: 10.1107/S2052252519000241. eCollection, 2019 Mar 1. PMID: 30867922

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