Coordination properties of Cu(II) ions towards the peptides based on the His-Xaa-His motif from Fusobacterium nucleatum P1 protein

The coordination capacity of the copper(II) ions with peptides (fragments of the P1 protein - one of the outer membrane protein from Fusobacterium nucleatum) based on the His-Xaa-His motif was carried out using potentiometric measurements, mass spectrometry and spectroscopic techniques: UV-Vis, CD and EPR. The selected tetrapeptides (Ac-HGHE-NH2, Ac-GHHE-NH2, Ac-HEHQ-NH2 and Ac-EHEH-NH2) form both mononuclear and bis-complexes with copper(II) ions. In the case of mononuclear complexes the CuL and CuLH-2 species dominate in the solution, where the coordination sphere is create by {2 x N-1m} and {2 x N-1m,2 x N-amide(-)}, respectively. The Ac-HGHE-NH2 peptide form more stable the CuLH-2 complex with the 4N{2 x N-1m,2 x N-amide(-)} binding site compared to the other ligands. The presence of glutamic acid residue in sequence Ac-HEHQ-NH2 produced the destabilization of the CuLH-2 complex in comparison to that of the Ac-HGHE-NH2 sequence. For the CuLH-3 complex the coordination process for complexes containing a histidyl residue in the first positions (H-1) proceed towards C-terminal sequence of the peptide. The bis-complexes are formed in the solution, where the metal ion is bounded by four imidazole nitrogen atoms {4 x N-1m}.