3TM2:
reference: Autoproteolytic Activation of ThnT Results in Structural Reorganization Necessary for Substrate Binding and Catalysis., Buller AR, Labonte JW, Freeman MF, Wright NT, Schildbach JF, Townsend CA, J Mol Biol. 2012 Jun 15. PMID: 22706025

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