5KSC:
reference: Active Site Protonation States in an Acyl-enzyme Intermediate of a Class A beta-lactamase with a Monobactam Substrate., Vandavasi VG, Langan PS, Weiss KL, Parks JM, Cooper JB, Ginell SL, Coates L, Antimicrob Agents Chemother. 2016 Oct 24. pii: AAC.01636-16. PMID: 27795378

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