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In human pathogenic bacteria, nickel is required for the activation of two enzymes, urease and [NiFe]-hydrogenase, necessary for host infection. Acquisition of Ni(II) is mediated by either permeases or ABC-importers, the latter including a subclass that involves an extracytoplasmic nickel-binding protein, Ni-BP. This study reports on the structure of three Ni-BPs from a diversity of human pathogens and on the existence of three new nickel-binding motifs. These are different from that previously described for Escherichia coli Ni-BP NikA, known to bind nickel via a nickelophore, and indicate a variegated ligand selectivity for Ni-BPs. The structures are consistent with ligand affinities measured in solution by calorimetry and challenge the hypothesis of a general requirement of nickelophores for nickel uptake by canonical ABC importers. Phylogenetic analyses showed that Ni-BPs have different evolutionary origins and …