3BQA:
reference: Crystal structure of a functional simer of the PhoQ sensor domain., Cheung J, Bingman CA, Reyngold M, Hendrickson WA, Waldburger CD, J Biol Chem. 2008 Mar 18;. PMID: 18348979

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