6B7T:
reference: Structural Insight into the Photochemistry of Split Green Fluorescent Proteins: A Unique Role for a His-Tag., Deng A, Boxer SG, J Am Chem Soc. 2017 Dec 21. doi: 10.1021/jacs.7b10680. PMID: 29193968

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