title: Complexation abilities of neuropeptide gamma toward copper(II) ions and products of metal-catalyzed oxidation.
abstract: The stability constants, stoichiometry, and solution structures of copper(II) complexes of neuropeptide gamma (NPG) (D(1)-A-G-H(4)-G-Q-I-S-H(9)-K-R-H(12)-K-T-D-S-F-V-G-L-M(21)-NH(2)) and acethyl-neuropeptide gamma (Ac-D(1)-A-G-H(4)-G-Q-I-S-H(9)-K-R-H(12)-K-T-D-S-F-V-G-L-M(21)-NH(2)) were determined in aqueous solution. For both peptides the additional deprotonations were observed; therefore, the potentiometric data calculations for NPG were only made in 2.5-7.4 pH range. For Ac-NPG one additional deprotonation was observed, likely hydroxy group of Ser residue, and the potentiometric data calculations in the 2.5-10.5 pH range may be performed. The potentiometric and spectroscopic data (UV-vis, CD, EPR) for the neuropeptide gamma show that a D(1) residue stabilizes significantly the copper(II) complexes with 1N {NH(2),β-COO(-)}, 2N {NH(2),β-COO(-),N(Im)}, and 3N {NH(2),β-COO(-),2N(Im)} coordination modes as the result of coordination through the β-carboxylate group. The Ac-NPG forms with the copper(II) ions the 3N {3N(Im)} complex in a wide 4.5-7.5 pH range. At higher pH deprotonation and coordination of the sequential amide nitrogens occur. Metal-catalyzed oxidation of proteins is mainly a site-specific process in which amino acids at metal-binding sites to the protein are preferentially oxidized. To elucidate the products of the copper(II)-catalyzed oxidation of NPG and Ac-NPG the liquid chromatography-mass spectrometry method (LC-MS) and the Cu(II)/H(2)O(2) as a model oxidizing system were employed. For solutions containing a 1:4 peptide-hydrogen peroxide molar ratio oxidation of the methionine residue to methionine sulphone was observed. For the 1:1:4 Cu(II)-NPG-H(2)O(2) system oxidation of two His residues and cleavage of the G(3)-H(4) and R(11)-H(12) peptide bonds were detected, supporting involvement of His(4) and His(12) in binding of the copper(II) ions. Oxidations of three histidine residues to 2-oxohistidines and fragmentations of Ac-NPG near the His (H(4), H(9),H(12)) residues support participation of the histidyl-imidazole nitrogen atoms in coordination of the metal ions.
authors.affiliation: Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wroclaw, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Pietruszka
authors.forename: Elżbieta
authors.initials: E
authors.lastname: Jankowska
authors.forename: Teresa
authors.initials: T
authors.lastname: Kowalik-Jankowska
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Szewczuk
authors.forename: Maria
authors.initials: M
authors.lastname: Smużyńska
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D007477:Ions; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D015320:Tachykinins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D007477:Ions; D010446:Peptide Fragments; D015320:Tachykinins; C059905:tachykinin neuropeptide gamma; D003300:Copper