6FTS:
reference: Modular organisation of inducer recognition and allostery in the tetracycline repressor., Werten S, Schneider J, Palm GJ, Hinrichs W, FEBS J. 2016 Mar 30. doi: 10.1111/febs.13723. PMID: 27028290

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