1YZW:
reference: The 2.1A Crystal Structure of the Far-red Fluorescent Protein HcRed: Inherent Conformational Flexibility of the Chromophore., Wilmann PG, Petersen J, Pettikiriarachchi A, Buckle AM, Smith SC, Olsen S, Perugini MA, Devenish RJ, Prescott M, Rossjohn J, J Mol Biol 2005 May 27;349(1):223-37. Epub 2005 Mar 22. PMID: 15876379

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