Physiological role of S-formylglutathione hydrolase in C1 metabolism of the methylotrophic yeast Candida boidinii

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Abstract
The methylotrophic yeastCandida boidiniiexhibitsS-formylglutathione hydrolase activity (FGH, EC 3.1.2.12), which is involved in the glutathione-dependent formaldehyde oxidation pathway during growth on methanol as the sole carbon source. The structural gene,FGH1, was cloned fromC. boidinii, and its predicted amino acid sequence showed more than 60 % similarity to those of FGHs fromParacoccus denitrificansandSaccharomyces cerevisiae, and human esterase D. FGH fromC. boidiniicontained a C-terminal tripeptide, SKL, which is a type I peroxisome-targeting signal, and a bimodal distribution of FGH between peroxisomes and the cytosol was demonstrated. TheFGH1gene was disrupted in theC. boidiniigenome by one-step gene disruption. Thefgh1Δ strain was still able to grow on methanol as a carbon source under methanol-limited chemostat conditions with low dilution rates (D−1), conditions under which a strain with disruption of the gene for formaldehyde dehydrogenase (another enzyme involved in the formaldehyde oxidation pathway) could not survive. These results suggested that FGH is not essential but necessary for optimal growth on methanol. This is believed to be the first report of detailed analyses of theFGH1gene in a methylotrophic yeast strain.