4V2F:
reference: Tetracycline Repressor Allostery Does Not Depend on Divalent Metal Recognition., Werten S, Dalm D, Palm GJ, Grimm CC, Hinrichs W, Biochemistry. 2014 Dec 9. PMID: 25432019

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