6B3U:
reference: Tilted, Uninterrupted, Monomeric HIV-1 gp41 Transmembrane Helix from Residual Dipolar Couplings., Chiliveri SC, Louis JM, Ghirlando R, Baber JL, Bax A, J Am Chem Soc. 2018 Jan 10;140(1):34-37. doi: 10.1021/jacs.7b10245. Epub 2017 Dec, 27. PMID: 29277995

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