Candida albicans expresses an unusual cytoplasmic manganese-containing superoxide dismutase (SOD3 gene product) upon the entry and during the stationary phase

We report here that in addition to a cytoplasmic copper-zinc-containing sup eroxide dismutase (SOD) and a mitochondrial manganese-containing SOD, Candi da albicans expresses a third SOD gene (SOD3). The deduced amino acid seque nce contains all of the motifs found in previously characterized manganese- containing SODs, except the presence of a mitochondrial transit peptide. Re combinant Sod3p expressed and purified from Escherichia coli is a homotetra mer with a subunit mass of 25.4 kDa. Mass absorption spectrometry detected the presence of both iron and manganese in purified Sod3p but, as determine d by metal replacement experiments, the enzyme displays activity only when bound to manganese. Overexpression of SOD3 was shown to rescue the hypersen sitivity to redox cycling agents of a Saccharomyces cerevisiae mutant lacki ng the cytoplasmic copper-zinc-containing SOD. Northern blot analyses showe d that the transcription of SOD3 is induced neither by the transition from the yeast to the mycelial form of C. albicans nor by drug-induced oxidative stress. In continuous cultures, the expression of SOD3 was strongly stimul ated upon the entity and during the stationary phase, concomitantly with th e repression of SOD1. We conclude that Sod3p is an atypical cytosolic manga nese-containing superoxide dismutase that is involved in the protection of C. albicans against reactive oxygen species during the stationary phase.