Issue 6, 2012

Coordination of copper(ii) ions by the fragments of neuropeptide gamma containing D1, H9, H12 residues and products of copper-catalyzed oxidation

Abstract

A potentiometric, spectroscopic (UV-Vis, CD and EPR) and mass spectrometric (ESI-MS) study of Cu(II) binding to the (1-2,7-21)NPG, Asp1-Ala-Ile7-Ser-His9-Lys-Arg-His12-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met21-NH2, and Ac-(1-2,7-21)NPG, Ac-Asp1-Ala-Ile7-Ser-His9-Lys-Arg-His12-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met21-NH2, fragments of neuropeptide gamma were carried out. The results clearly indicate the stabilization of the 1 N {NH2, β-COO}, 2 N {NH2, β-COO, NIm} and 3 N {NH2, β-COO, 2NIm} complexes by the coordination of the β-carboxylate group of the D1 residue. For the (1-2,7-21)NPG the CuH2L complex with 3 N {NH2, β-COO, 2NIm}, the binding mode dominates in a wide pH range of 4–8.5. With the sequential increase of pH, deprotonated amide nitrogens are involved in copper coordination. For the Ac-(1-2,7-21)NPG peptide the imidazole nitrogen atoms are the primary metal binding sites forming macrochelates in the pH range 4 to 7. The CuHL complex with 4 N {NIm, N, N, NIm} coordination mode is formed in pH range 6–9. Deprotonation and co-ordination of the third amide nitrogen were detected at pH ∼8.6. Metal-catalyzed oxidation (MCO) of proteins is mainly a site-specific process in which one or a few amino acids at metal-binding sites on the protein are preferentially oxidized. To elucidate the products of the copper(II)-catalyzed oxidation of the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG, the liquid chromatography-mass spectrometry (LC-MS) method and Cu(II)/hydrogen peroxide as a model oxidizing system were employed. In the presence of hydrogen peroxide with 1 : 4 peptide–H2O2 molar ratio for the Ac-(1-2,7-21)NPG peptide the oxidation of the methionine residue to methionine sulfoxide and for (1-2,7-21)NPG to sulfone was observed. For the Cu(II)–peptide–hydrogen peroxide in 1 : 1 : 4 molar ratio systems, oxidation of the histidine residues to 2-oxohistidines was detected. Under experimental conditions the (1-2,7-21)NPG and Ac-(1-2,7-21)NPG undergo fragmentations by cleavage of the S8-H9, H9-K10, R11-H12 and H12-K13 peptide bonds supporting the participation of the H9 and H12 residues in the coordination of copper(II) ions. For the (1-2,7-21)NPG peptide chain the involvement of the D1 residue in the coordination of metal ions is supported by the alkoxyl radical modification of this amino acid residue.

Graphical abstract: Coordination of copper(ii) ions by the fragments of neuropeptide gamma containing D1, H9, H12 residues and products of copper-catalyzed oxidation

Supplementary files

Article information

Article type
Paper
Submitted
07 Apr 2011
Accepted
01 Nov 2011
First published
13 Dec 2011

Dalton Trans., 2012,41, 1683-1694

Coordination of copper(II) ions by the fragments of neuropeptide gamma containing D1, H9, H12 residues and products of copper-catalyzed oxidation

E. Jankowska, M. Pietruszka and T. Kowalik-Jankowska, Dalton Trans., 2012, 41, 1683 DOI: 10.1039/C1DT10592B

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