2QWS:
reference: Neutron and X-ray structural studies of short hydrogen bonds in photoactive yellow protein (PYP)., Fisher SZ, Anderson S, Henning R, Moffat K, Langan P, Thiyagarajan P, Schultz AJ, Acta Crystallogr D Biol Crystallogr. 2007 Nov;63(Pt 11):1178-84. Epub 2007, Oct 17. PMID: 18007033

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