1XPT:
reference: Plasticity, hydration and accessibility in ribonuclease A. The structure of a new crystal form and its low-humidity variant., Sadasivan C, Nagendra HG, Vijayan M, Acta Crystallogr D Biol Crystallogr 1998 Nov 1;54(Pt 6 Pt 2):1343-52. PMID: 10089510

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