Damages to Zn2+and Cd2+ complexes of a metallothionein (MT) from a plant (Quercus suber - Qs), due to radicai stress exposure, were investigated. QsMT, obtained by in vivo synthesis, is a low-molecular weight cysteine-rich protein with high capacity for binding metal ions. Although MTs do not appear to be essential for life, there is mounting evidences for a survival advantage of MT in situations of stress, including exposure to radicals and toxic metals. Gamma-irradiation was used to simulate the conditions of an endogenous radical stress. The degradation of the metal complexes was followed by Raman spectroscopy and the occurrence of tandem protein/lipid damage was shown by using a biomimetic model based on unsaturated lipid vesicle suspensions. The H1 and eaq- attacks on the metal-QsMT aggregates are able to induce significant structural changes such as partial deconstruction and/or rearrangement of the metal clusters, and breaking of the protein backbone. Sulfur-containing residues resulted to be selectively attacked; in particular, Cys resulted to be among the most sensitive residues towards radical attack, suggesting that the thiolate clusters of both metal-QsMTs act as efficient interceptors of reducing species. Under reductive stress Zn-QsMT undergoes a significant thiolate group oxidation. The participation of His to metal coordination became necessary for protein stabilization after radical stress. The radical-induced effects were dependent on the divalent metal bound. The reactions of reductive reactive species with Met residues and/or sulfur-containing ligands afford diffusible sulfur-centered radicals, which migrate from the aqueous phase to the lipid bilayer and transform the cis doublé bond of thè oleate moiety to the trans isomer.
Metal complexes of a plant metallothionein under radical stress: assessment of structural modifications and transfer of radical damage.
TINTI, ANNA;
2009
Abstract
Damages to Zn2+and Cd2+ complexes of a metallothionein (MT) from a plant (Quercus suber - Qs), due to radicai stress exposure, were investigated. QsMT, obtained by in vivo synthesis, is a low-molecular weight cysteine-rich protein with high capacity for binding metal ions. Although MTs do not appear to be essential for life, there is mounting evidences for a survival advantage of MT in situations of stress, including exposure to radicals and toxic metals. Gamma-irradiation was used to simulate the conditions of an endogenous radical stress. The degradation of the metal complexes was followed by Raman spectroscopy and the occurrence of tandem protein/lipid damage was shown by using a biomimetic model based on unsaturated lipid vesicle suspensions. The H1 and eaq- attacks on the metal-QsMT aggregates are able to induce significant structural changes such as partial deconstruction and/or rearrangement of the metal clusters, and breaking of the protein backbone. Sulfur-containing residues resulted to be selectively attacked; in particular, Cys resulted to be among the most sensitive residues towards radical attack, suggesting that the thiolate clusters of both metal-QsMTs act as efficient interceptors of reducing species. Under reductive stress Zn-QsMT undergoes a significant thiolate group oxidation. The participation of His to metal coordination became necessary for protein stabilization after radical stress. The radical-induced effects were dependent on the divalent metal bound. The reactions of reductive reactive species with Met residues and/or sulfur-containing ligands afford diffusible sulfur-centered radicals, which migrate from the aqueous phase to the lipid bilayer and transform the cis doublé bond of thè oleate moiety to the trans isomer.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
