4KXY:
reference: Sub-angstrom-resolution crystallography reveals physical distortions that enhance reactivity of a covalent enzymatic intermediate., Ludtke S, Neumann P, Erixon KM, Leeper F, Kluger R, Ficner R, Tittmann K, Nat Chem. 2013 Sep;5(9):762-7. doi: 10.1038/nchem.1728. Epub 2013 Aug 18. PMID: 23965678

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