Isolation, characterization and crystallization of an iron-superoxide dismutase from the crenarchaeon Sulfolobus acidocaldarius

An iron containing superoxide dismutase from the cytosol of the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius (DSM 639) has been purified to electrophoretic homogeneity. It comprises at least 11% of the cytosolic protein. The isolated protein consists of two identical subunits with an apparent molecular mass of 22.4 kDa. It contains one iron atom per dimer. The protein shows the typical EPR spectrum of a S = 3/2, rhombic high-spin iron center. It is extremely resistant against thermal and chemical denaturation. Simultaneous treatment with heat and detergent resulted in the conversion into a more active tetrameric form. Similar enzymes appear to be present in the cytosol of other members of the Sulfolobaceae. The dimeric form of the protein from S. acidocaldarius has been crystallized.