Superoxide dismutase (SOD) is a metal enzyme playing a key role in the cell defence mechanism against the reactive oxygen species (ROS). High levels of ROS are involved in several pathologic states such as senescence, cell death and cancer. SODs are widely studied as potential therapeutic agents in pathologies correlated with oxidative stress. SODs are usually classified in two main structurally unrelated families on the basis of their metal content in the active site. The family of Fe- and Mn-SODs is found in eubacteria, archaea and mitochondria and this ubiquitous distribution probably reflects the most crucial antioxidant function of this enzyme. The modulation of SOD activity is essential during oxidative stress; data have been reported on the regulation of Fe- and Mn-SODs by covalent modifications. SODs isolated from extremophilic sources represent models to study the structure-function relationships of proteins adapted to extreme conditions, and the role of modifications in the enyme function. This report describes the biochemical and functional characterization of superoxide dismutase from the psychrophilic eubacterium Pseudoalteromonas haloplanktis (PhSOD). The enzyme, an iron-containing homodimer, is endowed with a high specific activity even at low temperatures, and displays a thermal resistance well above the growth temperature of P. haloplanktis. PhSOD is very sensitive to peroxynitrite, a physiological inactivator of mitochondrial Mn-SOD, acting on Tyr34. PhSOD has a unique and highly reactive cysteine residue (Cys57), located in a variable region of the protein. The three-dimensional model of PhSOD indicates that the structural organization of this region discriminates between dimeric and tetrameric SODs. Cys57 forms a disulfide bond with beta-mercaptoethanol in native conditions, whereas in specific denaturing conditions, two subunits of PhSOD form a covalent dimer. The modification by beta-mercaptoethanol has little effect on the enzyme activity, but significantly affects the tyrosine nitration, protecting the enzyme from inactivation. Covalent modification by cellular thiols, such as glutathione, on proteins containing highly reactive –SH groups plays an essential role in the regulation of the cellular redox state. Indeed, we have found that PhSOD is covalently modified by glutathione in vitro. Further investigation concerns the possible modification of PhSOD by glutathione in P. haloplanktis cells, upon induction of oxidative stress.

A highly reactive cysteine is involved in the antioxidant function of superoxide dismutase from the psychrophilic eubacterium Pseudoalteromonas haloplanktis / Castellano, I; Ruocco, MARIA ROSARIA; DI MARO, A; Chambery, A; Parente, A; Masullo, M; DE VENDITTIS, Emmanuele. - (2006), pp. 294-294. (Intervento presentato al convegno 8th European Biological Inorganic Chemistry Conference and Eurobic Young Researchers Forum tenutosi a Aveiro (Portugal) nel 1-6 July 2006).

A highly reactive cysteine is involved in the antioxidant function of superoxide dismutase from the psychrophilic eubacterium Pseudoalteromonas haloplanktis

CASTELLANO I;RUOCCO, MARIA ROSARIA;DE VENDITTIS, EMMANUELE
2006

Abstract

Superoxide dismutase (SOD) is a metal enzyme playing a key role in the cell defence mechanism against the reactive oxygen species (ROS). High levels of ROS are involved in several pathologic states such as senescence, cell death and cancer. SODs are widely studied as potential therapeutic agents in pathologies correlated with oxidative stress. SODs are usually classified in two main structurally unrelated families on the basis of their metal content in the active site. The family of Fe- and Mn-SODs is found in eubacteria, archaea and mitochondria and this ubiquitous distribution probably reflects the most crucial antioxidant function of this enzyme. The modulation of SOD activity is essential during oxidative stress; data have been reported on the regulation of Fe- and Mn-SODs by covalent modifications. SODs isolated from extremophilic sources represent models to study the structure-function relationships of proteins adapted to extreme conditions, and the role of modifications in the enyme function. This report describes the biochemical and functional characterization of superoxide dismutase from the psychrophilic eubacterium Pseudoalteromonas haloplanktis (PhSOD). The enzyme, an iron-containing homodimer, is endowed with a high specific activity even at low temperatures, and displays a thermal resistance well above the growth temperature of P. haloplanktis. PhSOD is very sensitive to peroxynitrite, a physiological inactivator of mitochondrial Mn-SOD, acting on Tyr34. PhSOD has a unique and highly reactive cysteine residue (Cys57), located in a variable region of the protein. The three-dimensional model of PhSOD indicates that the structural organization of this region discriminates between dimeric and tetrameric SODs. Cys57 forms a disulfide bond with beta-mercaptoethanol in native conditions, whereas in specific denaturing conditions, two subunits of PhSOD form a covalent dimer. The modification by beta-mercaptoethanol has little effect on the enzyme activity, but significantly affects the tyrosine nitration, protecting the enzyme from inactivation. Covalent modification by cellular thiols, such as glutathione, on proteins containing highly reactive –SH groups plays an essential role in the regulation of the cellular redox state. Indeed, we have found that PhSOD is covalently modified by glutathione in vitro. Further investigation concerns the possible modification of PhSOD by glutathione in P. haloplanktis cells, upon induction of oxidative stress.
2006
9789892003054
A highly reactive cysteine is involved in the antioxidant function of superoxide dismutase from the psychrophilic eubacterium Pseudoalteromonas haloplanktis / Castellano, I; Ruocco, MARIA ROSARIA; DI MARO, A; Chambery, A; Parente, A; Masullo, M; DE VENDITTIS, Emmanuele. - (2006), pp. 294-294. (Intervento presentato al convegno 8th European Biological Inorganic Chemistry Conference and Eurobic Young Researchers Forum tenutosi a Aveiro (Portugal) nel 1-6 July 2006).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/118304
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