3TCH:
reference: Escherichia coli peptide binding protein OppA has a preference for positively charged peptides., Klepsch MM, Kovermann M, Low C, Balbach J, Permentier HP, Fusetti F, de Gier JW, Slotboom DJ, Berntsson RP, J Mol Biol. 2011 Nov 18;414(1):75-85. Epub 2011 Oct 1. PMID: 21983341

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