Cloning and characterization of iron-superoxide dismutase in Antarctic yeast strain Rhodotorula mucilaginosa AN5

A novel superoxide dismutase gene from Antarctic yeast Rhodotorula mucilaginosa AN5 was cloned, sequenced, and then expressed in Escherichia coli. The R. mucilaginosa AN5 SOD (RmFeSOD) gene was 639 bp open reading frame in length, which encoded a protein of 212 amino acids with a deduced molecular mass of 23.5 kDa and a pI of 7.89. RmFeSOD was identified as iron SOD type with a natural status of homodimer. The recombinant RmFeSOD showed good pH stability in the pH 1.0-9.0 after 1 h incubation. Meanwhile, it was found to behave relatively high thermostability, and maintained more than 80% activity at 50 degrees C for 1 h. By addition of 1 mM metal ions, the enzyme activity increased by Zn2+, Cu2+, Mn2+, and Fe3+, and inhibited only by Mg2+. RmFeSOD showed relatively low tolerance to some compounds, such as PMSF, SDS, Tween-80, Triton X-100, DMSO, beta-ME, and urea. However, DTT showed no inhibition to enzyme activity. Using copper stress experiment, the RmFeSOD recombinant E. coli exhibited better growth than nonrecombinant bacteria, which revealed that RmFeSOD might play an important role in the adaptability of heavy metals.