6C7Z:
reference: A Genetically Encoded Ratiometric pH-Probe: Wavelength Regulation-Inspired Design of pH Indicators., Berbasova T, Tahmasebi Nick S, Nosrati M, Nossoni Z, Santos E, Vasileiou C, Geiger J, Borhan B, Chembiochem. 2018 Apr 12. doi: 10.1002/cbic.201800050. PMID: 29645331

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