title: The yeast IRC7 gene encodes a β-lyase responsible for production of the varietal thiol 4-mercapto-4-methylpentan-2-one in wine.
abstract: Three varietal thiols are key aroma compounds in Sauvignon Blanc wines: 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexanol (3MH) and its acetylated derivative 3-mercaptohexyl acetate (3MHA). Screening of Saccharomyces cerevisiae strains identified a clinical isolate with elevated 4MMP production after fermentation. Bulked Segregant Analysis of a cross between this isolate and the laboratory strain revealed a single major locus for 4MMP production near the telomere of chromosome 6. Deletion of the IRC7 gene from this region in YJM450 reduced 4MMP production below detectable levels, but did not affect yields of 3MH, in Sauvignon Blanc wine. Sequencing revealed that the IRC7 gene in YJM450 had been introgressed from a strain of Saccharomyces paradoxus. Most strains of S. cerevisiae, including the laboratory strain S288C, have a 38-bp deletion that inactivates IRC7. Overexpression of a full-length S. cerevisiae allele of IRC7 in a wine yeast, Zymaflore F15, increased 4MMP production in Sauvignon Blanc wine from undetectable levels (<10 ng L(-1)) to concentrations of 1000 ng L(-1), and also increased 3MH and 3MHA. Biochemical analysis of soluble protein extracts showed that both the cerevisiae and paradoxus IRC7 proteins show β-lyase activity, with a substrate preference for cys-4MMP over cys-3MH.
authors.affiliation: Wine Science Programme, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Miguel
authors.initials: M
authors.lastname: Roncoroni
authors.forename: Margarita
authors.initials: M
authors.lastname: Santiago
authors.forename: David O
authors.initials: DO
authors.lastname: Hooks
authors.forename: Sarah
authors.initials: S
authors.lastname: Moroney
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Harsch
authors.forename: Soon A
authors.initials: SA
authors.lastname: Lee
authors.forename: Keith D
authors.initials: KD
authors.lastname: Richards
authors.forename: Laura
authors.initials: L
authors.lastname: Nicolau
authors.forename: Richard C
authors.initials: RC
authors.lastname: Gardner
mesh_terms: D000595:Amino Acid Sequence; D008969:Molecular Sequence Data; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D014920:Wine / Q000382:microbiology*
chemical_list: D013438:Sulfhydryl Compounds