Interaction of Cu(II)with His‐Val‐Gly‐Asp and of Zn(II)with His‐Val‐His, Two Peptides at the Active Site ofCu,Zn‐Superoxide Dismutase

Abstract

His-Val-His and His-Val-Gly-Asp are two naturally occurring peptide sequences, present at the active site of Cu,Zn-superoxide dismutase (Cu,Zn-SOD). We have already studied the interaction of His-Val-His=A (copper binding site) with Cu(II) and of His-Val-Gly-Asp=B (zinc binding site) with Zn(II). As a continuation of this work and for comparison purposes we have also studied the interaction of Zn(II) with His-Val-His and Cu(II) with His-Val-Gly-Asp using both potentiometric and spectroscopic methods (visible, EPR, NMR). The stoichiometry, stability constants and solution structure of the complexes formed have been determined. Histamine type of coordination is observed for/ZnAH/2+, /ZnA/+, /ZnA2H/+ and/ZnA2/ in acidic pH while deprotonation of coordinated water molecules is observed at higher pH. /CUB/ species is characterized by the formation of a macrochelate and histamine type coordination. Its stability results in the suppression of amide deprotonation which occurs at high pH resulting in the formation of the highly distorted from square planar geometry 4N complex/CuBH-3/3.

Copper(II) and zinc(II) complexes of the peptides Ac-HisValHis-NH 2 and Ac-HisValGlyAsp-NH 2 related to the active site of the enzyme CuZnSOD

“…The results obtained for the metal complexes of the non-protected peptide, HisValHis, have already been published from our laboratories and the data indicated that the ligand is a strong chelating agent for both copper(II) and zinc(II) [12,13]. The metal ion speciation of the copper(II)-Ac-HisValHis-NH 2 system is shown in Fig.…”

“…Copper(II) and zinc(II) complexes of the non-protected forms of the peptides HisValHis and HisValGlyAsp were thoroughly studied in our laboratories and the results have been published recently [12,13]. These Inorganic Biochemistry studies reveal that both peptides have outstanding metal binding ability and versatile coordination chemistry.…”

On the possible roles of N-terminal His-rich domains of Cu,Zn SODs of some Gram-negative bacteria

“…Later, the cleavage site between the positions 21 and 22 has been proposed [8]. Unfortunately, the protein used to prepare single crystals [25] lacks the whole N-terminal domain and starts only from 29 …”

“…The peptide has six readily available binding sites for zinc(II) ( [27][28][29]. However, the equilibrium constant of the process Zn 2+ + H 2 L = ZnH 2 L (log K = 6.58) is higher than the related value for histamine itself (log  101 = 5.15 [30]), or those of some {3N im } and {NH 2 ,2N im } coordinated complexes (log K = 5.1 [31] and 5.94 [29], respectively), indicating that additional binding sites should be taken into consideration. [12,34].…”

“…Such complexes of peptides with unprotected N-terminal histidine generally have bis-histamine {2NH 2 ,2N im } type binding [27][28][29], which provides relatively high stability (e.g. log K = 10.05 in the case of HVGD peptide [28]) .…”