1PFM:
reference: NMR solution structure of the 32-kDa platelet factor 4 ELR-motif N-terminal chimera: a symmetric tetramer., Mayo KH, Roongta V, Ilyina E, Milius R, Barker S, Quinlan C, La Rosa G, Daly TJ, Biochemistry 1995 Sep 12;34(36):11399-409. PMID: 7547867

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