Differential Expression of Superoxide Dismutases Containing Ni and Fe/Zn in Streptomyces Coelicolor

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Abstract
Streptomyces coelicolor contains two distinct superoxide dismutase (SOD) activities detected on native PAGE. The level of each changed differently depending on growth media and scarcely responded to paraquat, a superoxide-generating agent. The total SOD activity doubled in late exponential phase compared with that in mid-exponential phase and less than double upon treatment with plumbagin, another superoxide-generating agent. The two SODs from S. coelicolor ATCC 10147 (Müller) strain were purified to near homogeneity. SOD1, a tetramcr of 13.4-kDa subunits, was found to be a novel type of SOD containing 0.74 mol nickel/mol subunit as determined by atomic absorption spectroscopy. SOD2, a tetramer of 22.2-kDa subunits, was found to contain 0.36 mol iron and 0.26 mol zinc/mol subunit. The N-terminal amino acid sequences of both SODs were determined. SOD2 is similar to manganese-containing superoxide dismutases (MnSODs) and iron-containing superoxide dismutases (FeSODs) from other organisms, whereas SOD1 is less similar to known SODs but still contains a few conserved amino acids. The effects of metals and chelating agents on the expression of these two SODS were examined. The presence of nickel at micromolar concentrations in growth media induced the expression of SOD1 (nickel-containing superoxidc dismutase; NiSOD), whereas the expression of SOD2 (iron/zinc-containing superoxide dismutase; FeZnSOD) was repressed. The changes in SOD activities were positively correlated with the amount of each enzyme as determined by immunoblotting, suggesting that metals do not modulate the activity per se but the amount of each protein.