The ABC-type importer NikABCDE mediates nickel acquisition in Escherichia coli.
The periplasmic nickel-binding component NikA has a folding similar to that of
the peptide transporter OppA and does not bind free nickel. Instead, we showed
that the metal is tetra-coordinated by an organic tri-dentate molecule and
His416. Conversely, it has been recently reported that NikA binds
Ni-((L)-His)(2) and that addition of histidine increases the rate of nickel
uptake in vivo. Here, we report the structure of NikA/Ni-((L)-His)(2) and show
that histidine binding differs from peptide binding in OppA. The structure also
confirms the central role of His416 in nickel binding.
