4KGF:
reference: Extended Stokes shift in fluorescent proteins: chromophore-protein interactions in a near-infrared TagRFP675 variant., Piatkevich KD, Malashkevich VN, Morozova KS, Nemkovich NA, Almo SC, Verkhusha VV, Sci Rep. 2013;3:1847. doi: 10.1038/srep01847. PMID: 23677204

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