1FMA:
reference: Crystal structure of molybdopterin synthase and its evolutionary relationship to ubiquitin activation., Rudolph MJ, Wuebbens MM, Rajagopalan KV, Schindelin H, Nat Struct Biol 2001 Jan;8(1):42-6. PMID: 11135669

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