1P2N:
reference: Structural consequences of accommodation of four non-cognate amino acid residues in the S1 pocket of bovine trypsin and chymotrypsin., Helland R, Czapinska H, Leiros I, Olufsen M, Otlewski J, Smalas AO, J Mol Biol 2003 Oct 31;333(4):845-61. PMID: 14568540

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