Radical-induced damages to Substance P (SP), a small sulfur-containing oligopeptide involved in the transmission of pain information, were investigated. Exposure of proteins to free radicals may cause structural and functional changes. In particular, a single radical event that leads to an initial damage involving sulfur-containing amino acid residues can produce reactive species able to damage another cell compartment such as membrane lipid domains. We were interested in the reactivity of this low molecular weight protein under free radical conditions in order to envisage modifications other than purely oxidative ones and to have a wide scenario of the possible amino acid mutations. SP contains 11 amino acid residues of which one Met and two Phe residues. It is thought to be involved in a diverse range of important physiological processes, including inflammation. The wide range of physiological activities of SP has been ascribed to the lack of selectivity for a specific receptor type. The protein degradation due to radical exposure was evaluated by Raman spectroscopy as well as by MS experiments which provided valuable information on conformational changes of the protein secondary structure and the main sites of attack. Experiments were carried out in both aqueous solutions and vesicle suspensions. Free radical generation, mimicking an endogenous radical stress, was obtained by gamma-irradiation of aqueous solutions. By changing the appropriate conditions of irradiation, a selection of the reacting radical species was carried out. As previously observed for other sulfur-containing proteins, the reaction of reductive reactive species with the Met residue gives rise to diffusible sulfur-centered radicals, which migrate from the aqueous phase to the lipid bilayer and transform the cis double bond of the oleate moiety to the trans isomer (Fig. 1). The radical-induced effects were significantly dependent on pH as well as the peptide conformation. Protein structure play an important role in blocking the ready access of free radicals to the sulfur-containing residue, so strongly affecting the potential of the tandem radical damage.
Radical Stress and Substance P: assessment of structural modifications and transfer of radical damage
A Torreggiani;C Ferreri;C Chatgilialoglu
2010
Abstract
Radical-induced damages to Substance P (SP), a small sulfur-containing oligopeptide involved in the transmission of pain information, were investigated. Exposure of proteins to free radicals may cause structural and functional changes. In particular, a single radical event that leads to an initial damage involving sulfur-containing amino acid residues can produce reactive species able to damage another cell compartment such as membrane lipid domains. We were interested in the reactivity of this low molecular weight protein under free radical conditions in order to envisage modifications other than purely oxidative ones and to have a wide scenario of the possible amino acid mutations. SP contains 11 amino acid residues of which one Met and two Phe residues. It is thought to be involved in a diverse range of important physiological processes, including inflammation. The wide range of physiological activities of SP has been ascribed to the lack of selectivity for a specific receptor type. The protein degradation due to radical exposure was evaluated by Raman spectroscopy as well as by MS experiments which provided valuable information on conformational changes of the protein secondary structure and the main sites of attack. Experiments were carried out in both aqueous solutions and vesicle suspensions. Free radical generation, mimicking an endogenous radical stress, was obtained by gamma-irradiation of aqueous solutions. By changing the appropriate conditions of irradiation, a selection of the reacting radical species was carried out. As previously observed for other sulfur-containing proteins, the reaction of reductive reactive species with the Met residue gives rise to diffusible sulfur-centered radicals, which migrate from the aqueous phase to the lipid bilayer and transform the cis double bond of the oleate moiety to the trans isomer (Fig. 1). The radical-induced effects were significantly dependent on pH as well as the peptide conformation. Protein structure play an important role in blocking the ready access of free radicals to the sulfur-containing residue, so strongly affecting the potential of the tandem radical damage.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
