3CHG:
reference: The compatible-solute-binding protein OpuAC from Bacillus subtilis: ligand binding, site-directed mutagenesis, and crystallographic studies., Smits SH, Hoing M, Lecher J, Jebbar M, Schmitt L, Bremer E, J Bacteriol. 2008 Aug;190(16):5663-71. Epub 2008 Jun 20. PMID: 18567662

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