4I5V:
reference: Structures of yeast Apa2 reveal catalytic insights into a canonical AP(4)A phosphorylase of the histidine triad superfamily., Hou WT, Li WZ, Chen Y, Jiang YL, Zhou CZ, J Mol Biol. 2013 Aug 9;425(15):2687-98. doi: 10.1016/j.jmb.2013.04.018. Epub 2013, Apr 26. PMID: 23628156

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