4MZZ:
reference: X-ray crystal structure of bovine 3 Glu-osteocalcin., Malashkevich VN, Almo SC, Dowd TL, Biochemistry. 2013 Nov 26;52(47):8387-92. doi: 10.1021/bi4010254. Epub 2013 Nov, 12. PMID: 24138653

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