4NPF:
reference: Multiscale conformational heterogeneity in staphylococcal protein a: possible determinant of functional plasticity., Deis LN, Pemble CW 4th, Qi Y, Hagarman A, Richardson DC, Richardson JS, Oas TG, Structure. 2014 Oct 7;22(10):1467-77. doi: 10.1016/j.str.2014.08.014. PMID: 25295398

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