1HXQ:
reference: The structure of nucleotidylated histidine-166 of galactose-1-phosphate uridylyltransferase provides insight into phosphoryl group transfer., Wedekind JE, Frey PA, Rayment I, Biochemistry 1996 Sep 10;35(36):11560-9. PMID: 8794735

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