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

Abstract

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-GHEH-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 × N_Im} and {2 × N_Im,2 × N^-_amide}, respectively. The Ac-HGHE-NH₂ peptide form more stable the CuLH_-2 complex with the 4 N{2 × N_Im,2 × 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 (H¹) 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 × N_Im}.

Keywords: Copper(II) complexes; Fusobacterium nucleatum; Histidine; P1 protein; Peptide.