Poly-His and poly-Gln sequences in bacterial proteins: tempting sites for metal ions to interact with

Hpn and Hpn-like are Helicobacter pylori cytoplasmic proteins involved in the homeostasis of nickel; this metal is required for the enzymes urease and Ni-Fe hydrogenase, essential for the bacterium colonization in the human stomach. While almost half of Hpn sequence consists of polyhistydyl repeats, Hpn-like protein is rich in glutamine residues. In order to shed light on the role of the consecutive His and Gln residues in metal-ion binding, the present investigation is focused on the N-terminal domain of Hpn-like protein. Cu(II) and Ni(II) complexes of peptide models were studied by means of different thermodynamic and spectroscopic techniques, as well as through molecular modeling computations.