2RKS:
reference: A buried lysine that titrates with a normal pKa : Role of conformational flexibility at the protein-water interface as a determinant of pKa values., Harms MJ, Schlessman JL, Chimenti MS, Sue GR, Damjanovic A, Garcia-Moreno E B, Protein Sci. 2008 Mar 27;. PMID: 18369193

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