The binding abilities of homodetic cyclic His-peptides toward copper ions

Abstract

Abstract The biochemistry of copper is important and worthy to be broadly studied. In biological systems copper is usually bound by enzymes, proteins or peptides and the investigation of the occurring interactions is still a hot topic. In this overview we focus on the copper binding abilities of homodetic cyclic peptides (CPs) containing histidine moieties. This group of ligands is characterized by a cyclic ring composed only of amino acids. Several applications of cyclic peptides should be viable because of their special structures, stability and resistance against enzymatic degradation. The cyclic structure promotes the anchoring of metal ions by the amino acid side chains. We discuss the impact of peptide cyclization and ring size on the binding abilities toward copper(II) ions. We also compare the coordinating properties of ligands containing a different number of His residues with the (HX) n − motif, where X = Gly, Lys, Arg, Asn or Pro, based on the stability constants of nN Im (n = 2–4) complexes created by His 4 -cyclopeptides. In addition, we compare the sustainability and stability of nN Im (n = 1–4) complexes depending on the Asp residue in the peptide sequence and we also consider the aspects of forming dinuclear copper(II) complexes by cyclopeptides with two separated Pro residues in the sequence. The di-Cu(II)-complexes are favored in the basic pH range. So far, cyclopeptides found use in pharmaceutical chemistry, biochemistry, and life sciences, but also as ionophores and nano-materials. We advocate here to use their metal ion complexes because they enrich the spectrum of available activities of metallopeptides or change the properties of these ligands.