3ICB:
reference: The refined structure of vitamin D-dependent calcium-binding protein from bovine intestine. Molecular details, ion binding, and implications for the structure of other calcium-binding proteins., Szebenyi DM, Moffat K, J Biol Chem 1986 Jul 5;261(19):8761-77. PMID: 3722173

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