4A2S:
reference: Evolution of a designed retro-aldolase leads to complete active site remodeling., Giger L, Caner S, Obexer R, Kast P, Baker D, Ban N, Hilvert D, Nat Chem Biol. 2013 Jun 9. doi: 10.1038/nchembio.1276. PMID: 23748672

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