3QIM:
reference: Histidine 416 of the periplasmic binding protein NikA is essential for nickel uptake in Escherichia coli., Cavazza C, Martin L, Laffly E, Lebrette H, Cherrier MV, Zeppieri L, Richaud P, Carriere M, Fontecilla-Camps JC, FEBS Lett. 2011 Feb 18;585(4):711-5. Epub 2011 Feb 1. PMID: 21281641

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