4ITR:
reference: Structural basis of Fic-mediated adenylylation., Xiao J, Worby CA, Mattoo S, Sankaran B, Dixon JE, Nat Struct Mol Biol. 2010 Aug;17(8):1004-10. Epub 2010 Jul 11. PMID: 20622875

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