3PQS:
reference: Structural variations within the transferrin binding site on transferrin binding protein B, TbpB., Calmettes C, Yu RH, Silva LP, Curran D, Schriemer DC, Schryvers AB, Moraes TF, J Biol Chem. 2011 Feb 5. PMID: 21297163

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