title: Yeast genes required for conversion of grape precursors to varietal thiols in wine.
abstract: Three varietal thiols are important for the tropical fruit aromas of Sauvignon blanc: 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexanol (3MH) and its acetylated derivative 3-mercaptohexyl acetate (3MHA). These thiols are produced by yeast during fermentation from precursors in grape juice. Here we identify genes in Saccharomyces cerevisiae that are required for the transport and cleavage of two thiol precursors: cysteine-4MMP and glutathione-3MH. A full-length copy of IRC7 is absolutely required for the cleavage of both precursors in the tested strains; the deleted form of the enzyme found in most yeast strains is incapable of converting these compounds into detectable thiols. By using strains that overexpress full-length IRC7, we further show that the glutathione transporter OPT1 and the transpeptidase CIS2 are also required for conversion of glut-3MH to its varietal thiol. No transporter for cys-4MMP was identified: a strain deleted for all nine known cysteine transport genes was still capable of converting cys-4MMP to its varietal thiol, and was also able to take up cysteine at high concentrations. Based on these results, we conclude that cysteine and glutathione precursors make a relatively minor contribution to 3MH production from most grape juices.
authors.affiliation: Wine Science Programme, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand santiago.margarita@gmail.com.
authors.forename: Margarita
authors.initials: M
authors.lastname: Santiago
authors.affiliation: Wine Science Programme, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Gardner
mesh_terms: D000085:Acetates / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D013437:Carbon-Sulfur Lyases / Q000235:genetics* / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D004150:Dipeptidases / Q000235:genetics / Q000378:metabolism; D005285:Fermentation / Q000502:physiology; D005978:Glutathione / Q000378:metabolism; D000441:Hexanols / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D010422:Pentanones / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D027843:Vitis / Q000382:microbiology; D014920:Wine / Q000382:microbiology; D005723:gamma-Glutamyltransferase / Q000235:genetics / Q000378:metabolism
chemical_list: C501638:4-mercapto-4-methyl-pentan-2-one; D000085:Acetates; D000441:Hexanols; D009004:Monosaccharide Transport Proteins; C491110:OPT1 protein, S cerevisiae; D010422:Pentanones; D029701:Saccharomyces cerevisiae Proteins; D013438:Sulfhydryl Compounds; C513640:3-mercaptohexyl acetate; C000607134:Cis2 protein, S cerevisiae; D005723:gamma-Glutamyltransferase; C523458:DUG1 protein, S cerevisiae; D004150:Dipeptidases; D013437:Carbon-Sulfur Lyases; C000607133:Irc7 protein, S cerevisiae; D005978:Glutathione; D003545:Cysteine; C477019:3-mercaptohexanol
keywords: CIS2; DUG1; IRC7; OPT1; Saccharomyces cerevisiae; Sauvignon blanc; cysteine conjugates; glutathione conjugates