6UN2:
reference: Structural and spectroscopic characterization of photoactive yellow protein and photoswitchable fluorescent protein constructs containing heavy atoms., Romei MG, Lin CY, Boxer SG, J Photochem Photobiol A Chem. 2020 Oct 1;401. doi:, 10.1016/j.jphotochem.2020.112738. Epub 2020 Jun 30. PMID: 32753830

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