Cloning and characterization of a thermostable superoxide dismutase from the thermophilic bacterium Rhodothermus sp XMH10

A superoxide dismutase (SOD) gene was cloned from the thermophilic bacterium Rhodothermus sp. XMH10 for the first time and highly expressed in Escherichia coli. The Rhodothermus sp. XMH10 SOD (RhSOD) gene encodes 209 amino acids with a putative molecular weight of 23.6 kDa and a pI value of 5.53. The recombinant RhSOD was detected to be an iron type SOD and existed as a dimer on its natural status. Experiments revealed that this RhSOD showed high activity at 50-70 degrees C and pH 5.0. Compared to SODs from other thermophiles, it was highly thermostable, maintaining more than 90% of its activity after incubation at 70 degrees C for 12 h, only totally inactivated after more than 4-h incubation at 80 degrees C. It also showed much higher resistance to KCN, NaN3 and H2O2 as compared to other SODs.