4PPL:
reference: X-Ray Crystal Structure and Properties of Phanta, a Weakly Fluorescent Photochromic GFP-Like Protein., Don Paul C, Traore DA, Olsen S, Devenish RJ, Close DW, Bell TD, Bradbury A, Wilce MC, Prescott M, PLoS One. 2015 Apr 29;10(4):e0123338. doi: 10.1371/journal.pone.0123338., eCollection 2015. PMID: 25923520

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