A novel mechanism regulates H₂S and SO₂ production in Saccharomyces cerevisiae

Sulfite (SO₂) plays an important role in flavour stability in alcoholic beverages, whereas hydrogen sulfide (H₂S) has an undesirable aroma. To discover the cellular processes that control SO₂ and H₂S production, we screened a library of Saccharomyces cerevisiae deletion mutants. Deletion of 12 genes led to increased H₂S productivity. Ten of these genes are known to be involved in sulfur-containing amino acid metabolism, whereas UBI4 functions in the ubiquitin-proteasome system and SKP2 encodes an F-box-containing protein whose function is unknown. We found that the skp2 mutant accumulated H₂S and SO₂, because the adenosylphophosulfate kinase Met14p is a substrate of SCF^Skp2 and more stable in the skp2 mutant than in the wild-type strain. Furthermore, the skp2 mutant grew more slowly than the wild-type strain under nutrient-limited conditions. Metabolome analysis showed that the concentration of intracellular cysteine is lower in the skp2 mutant than in the wild-type strain. The slow growth of the skp2 mutant was due to a lower concentration of intracellular cysteine, because the addition of cysteine suppressed the slow growth. In the skp2 mutant, the cysteine biosynthesis proteins Str2p, Str3p and Str4p are more stable than in the wild-type strain. Moreover, supplementation with methionine, S-adenosylmethionine, S-adenosylhomocysteine and homocysteine also suppressed the slow growth. Overexpression of STR1 or STR4 caused a more severe defect in the skp2 mutant. These results suggest that the balance of methionine and cysteine biosynthesis is important for yeast cell growth. Thus, Skp2p is one of the key components regulating this balance and H₂S/SO₂ production.