Cu2+ and Ni2+ interactions with N-terminal fragments of Hpn and Hpn-like proteins from Helicobacter pylori: unusual impact of poly-Gln sequence on the complex stability.

The N-terminal protected and unprotected peptides MAHHEEQHG-NH(2), Ac-MAHHEEQHG-NH(2) from Hpn (Helicobacter histidine-rich protein) and MAHHEQQQQQQA-NH(2), Ac-MAHHEQQQQQQA-NH(2) from Hpn-like protein, respectively, were synthesized and their interactions with Cu(2+) and Ni(2+) ions were studied by potentiometric, UV-visible, CD, and EPR techniques. The studies have shown that because of their albumin-like sequence, unprotected peptides are very effective chelating agents for both studied metals. The presence of the hexa-glutamine sequence has very distinct impact on the stability of the complexes formed even if direct interactions with metal ions were not found. The much more effective Ni(2+) binding by Hpn-like N-terminal domain when compared to Hpn protein could be critical for different biological functions played by both proteins.