4NCO:
reference: Crystal Structure of a Soluble Cleaved HIV-1 Envelope Trimer., Julien JP, Cupo A, Sok D, Stanfield RL, Lyumkis D, Deller MC, Klasse PJ, Burton DR, Sanders RW, Moore JP, Ward AB, Wilson IA, Science. 2013 Oct 31. PMID: 24179159

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