title: Unravelling glutathione conjugate catabolism in Saccharomyces cerevisiae: the role of glutathione/dipeptide transporters and vacuolar function in the release of volatile sulfur compounds 3-mercaptohexan-1-ol and 4-mercapto-4-methylpentan-2-one.
abstract: Sulfur-containing aroma compounds are key contributors to the flavour of a diverse range of foods and beverages, such as wine. The tropical fruit characters of Sauvignon Blanc wines are attributed to the presence of the aromatic thiols 3-mercaptohexan-1-ol (3-MH), its acetate ester 3-mercaptohexyl acetate (3-MHA), and 4-mercapto-4-methylpentan-2-one (4-MMP). These aromatic thiols are not detectable in grape juice to any significant extent but are released by yeast during alcoholic fermentation. While the processes involved in the release of 3-MH and 4-MMP from their cysteinylated precursors have been studied extensively, degradation pathways for glutathione S-conjugates (GSH-3-MH and GSH-4-MMP) have not. In this study, a candidate gene approach was taken, focusing on genes known to play a role in glutathione and glutathione-S-conjugate turnover in Saccharomyces cerevisiae. Our results confirm the role of Opt1p as the major transporter responsible for uptake of GSH-3-MH and GSH-4-MMP, and identify vacuolar Ecm38p as a key determinant of 3-MH release from GSH-3-MH. ECM38 was unimportant, on the other hand, for release of 4-MMP, and abolition of vacuolar biogenesis caused an increase in the amount of 4-MMP released. The alternative cytosolic glutathione degradation pathway was not involved in release of either thiol from their glutathionylated precursors. Finally, cycling of GSH-3-MH and/or its breakdown intermediates between the cytosol and the vacuole or extracellular space was implicated in modulation of 3-MH formation. Together, these results provide new targets for development of yeast strains that optimize release of these potent volatile sulfur compounds, and further our understanding of the processes involved in glutathione-S-conjugate turnover.
authors.affiliation: The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia.
authors.forename: Antonio G
authors.initials: AG
authors.lastname: Cordente
authors.affiliation: The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia.
authors.forename: Dimitra L
authors.initials: DL
authors.lastname: Capone
authors.affiliation: The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia. chris.curtin@awri.com.au.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Curtin
mesh_terms: D001711:Biotransformation; D005978:Glutathione / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D010422:Pentanones / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism*
chemical_list: C443379:3-mercaptohexan-1-ol; C501638:4-mercapto-4-methyl-pentan-2-one; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; C491110:OPT1 protein, S cerevisiae; D010422:Pentanones; D029701:Saccharomyces cerevisiae Proteins; D013438:Sulfhydryl Compounds; C086860:glutathione transporter; C043912:peptide permease; D005978:Glutathione
keywords: Fermentation; Glutathione-S-conjugate; Volatile thiols; Wine; Yeast