4PNE:
reference: The structure of SpnF, a standalone enzyme that catalyzes [4 + 2] cycloaddition., Fage CD, Isiorho EA, Liu Y, Wagner DT, Liu HW, Keatinge-Clay AT, Nat Chem Biol. 2015 Mar 2. doi: 10.1038/nchembio.1768. PMID: 25730549

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