The homopentameric chlorite dismutase from Magnetospirillum sp.

• Chlorite dismutase (Cld) from Magnetospirillum sp. was isolated for the first time.
• The X-ray crystallographic structure was partially solved at 3 Å resolution.
• Cld is a homopentamer containing one b-type heme per monomer.
• The EPR signatures of as-prepared Cld samples are sensitive to the purification protocol.
• Optimal buffer, pH and temperature for chlorite reduction were established.

Chlorite dismutase (Cld) is a b-type heme containing enzyme that catalyzes the reduction of chlorite into chloride plus dioxygen. This enzyme has gained attention because it can be used in the development of bioremediation processes, biosensors, and controlled dioxygen production. In the present work, Cld was purified from Magnetospirillum sp. cells cultured anaerobically with acetate/perchlorate until stationary phase. Biochemical, spectroscopic and X-ray crystallography methods showed that Cld from Magnetospirillum sp. is a ~ 140 kDa homopentamer comprising ~ 27.8 kDa monomers. Preliminary X-ray crystallography studies confirmed the quaternary structure and the presence of one b-type heme per monomer. The EPR spectroscopic signature of the as-purified Cld samples is affected by the buffer composition used during the purification. Potassium phosphate buffer is the only buffer that affected neither the spectral nor the kinetic properties of Cld. Kinetic studies in solution revealed that Cld from Magnetospirillum sp. decomposes chlorite at high turnover rates with optimal pH 6.0. A temperature below 10 °C is required to avoid enzyme inactivation due to cofactor bleaching during turnover, and to achieve full substrate consumption. Cld kinetic parameters were not affected when kinetic assays were performed in the presence of air or under argon atmosphere, but chloride is a weak mixed inhibitor that modifies the EPR signal of as-prepared samples.

Chlorite dismutase (Cld) isolated from the perchlorate-reducing bacterium Magnetospirillum sp. is a 140 kDa homopentamer composed of ~ 28 kDa subunits. Each monomer harbors one b-type heme that constitutes the Cld active site where chlorite (ClO2−) is reduced to chloride (Cl−) plus dioxygen (O2(g)). Cld has several potential technological applications, for example in bioremediation processes, either to eliminate chlorite from wastewater or for sensing purposes. Also, Cld can be used for in situ generation of controlled amounts of O2(g) from chlorite salts either for medicinal applications or for the study of O2-utilizing enzymes.Figure optionsDownload as PowerPoint slide