4C2F:
reference: CtpB Assembles a Gated Protease Tunnel Regulating Cell-Cell Signaling during Spore Formation in Bacillus subtilis., Mastny M, Heuck A, Kurzbauer R, Heiduk A, Boisguerin P, Volkmer R, Ehrmann M, Rodrigues CD, Rudner DZ, Clausen T, Cell. 2013 Oct 24;155(3):647-58. doi: 10.1016/j.cell.2013.09.050. Epub 2013 Oct, 24. PMID: 24243021

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