4KP4:
reference: Visualizing autophosphorylation in histidine kinases., Casino P, Miguel-Romero L, Marina A, Nat Commun. 2014 Feb 6;5:3258. doi: 10.1038/ncomms4258. PMID: 24500224

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