Psychrophilic superoxide dismutase from Pseudoalteromonas haloplanktis: biochemical characterization and identification of a highly reactive cysteine residue

• Published in: Biochimie
• Main Authors: CASTELLANO I, DI MARO, Antimo, RUOCCO MR, CHAMBERY, Angela, PARENTE A, DI MARTINO MT, PARLATO G, MASULLO M, DE VENDITTIS E.
• Other Authors: Castellano, I, Ruocco, Mr, Chambery, Angela, Parente, A, DI MARTINO, Mt, Parlato, G, Masullo, M, DE VENDITTIS, E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2006
• Subjects: Covalent modification; Pseudoalteromonas haloplankti; Psychrophilic enzyme; Sulfhydryl reactivity; Superoxide dismutase; Antarctic; The Antarctic; Antarc*
• Online Access: http://hdl.handle.net/11591/181562; https://doi.org/10.1016/j.biochi.2006.04.005

A psychrophilic superoxide dismutase (SOD) has been characterized from the Antarctic eubacterium Pseudoalteromonas haloplanktis (Ph). PhSOD is a homodimeric iron-containing enzyme and displays a high specific activity, even at low temperature. The enzyme is inhibited by sodium azide and inactivated by hydrogen peroxide; it is also very sensitive to peroxynitrite, a physiological inactivator of the human mitochondrial Mn-SOD. Even though PhSOD is isolated from a cold-adapted micro-organism, its heat stability is well above the maximum growth temperature of P. haloplanktis, a feature common to other Fe- and Mn-SODs. The primary structure of PhSOD was determined by a combination of mass spectrometry and automated Edman degradation. The polypeptide chain is made of 192 amino acid residues, corresponding to a molecular mass of 21251 Da. The alignment with other Fe- and Mn-SODs showed a high amino acid identity with Fe-SOD from Vibrio cholerae (79%) and Escherichia coli (70%). A significant similarity is also shared with human mitochondrial Mn-SOD. PhSOD has the unique and highly reactive Cys57 residue, located in a variable region of the protein. The three-dimensional model of the PhSOD monomer indicates that Cys57 is included in a region, whose structural organization apparently discriminates between dimeric and tetrameric SODs. This residue forms a disulfide adduct with β-mercaptoethanol, when this reducing agent is added in the purification procedure. The reactivity of Cys57 leads also to the formation of a disulfide bridge between two PhSOD subunits in specific denaturing conditions. The possible modification of Cys57 by physiological thiols, eventually regulating the PhSOD functioning, is discussed. © 2006 Elsevier Masson SAS. All rights reserved.