title: Flavour formation in fungi: characterisation of KlAtf, the Kluyveromyces lactis orthologue of the Saccharomyces cerevisiae alcohol acetyltransferases Atf1 and Atf2.
abstract: Volatile aroma-active esters are responsible for the fruity character of fermented alcoholic beverages, such as beer and wine. In the brewers' yeast Saccharomyces cerevisiae, the major part of these esters is formed by two alcohol acetyltransferases, Atf1 and Atf2. In this paper, the existence of orthologues of these S. cerevisiae alcohol acetyltransferases in several ascomycetous fungi was investigated. Bioinformatic analysis of sequenced fungal genomes revealed the presence of multiple orthologues. The Saccharomyces sensu stricto yeasts all have two genes coding for orthologues. More distantly related fungi like Saccharomyces castelii, Candida glabrata, Kluyveromyces waltii and Kluyveromyces lactis have only one orthologue in their genome. The homology between the identified proteins and the S. cerevisiae alcohol acetyltransferases suggests a role for these orthologues in the aroma-active ester formation. To verify this, the K. lactis orthologue KlAtf was cloned and expressed in S. cerevisiae. Gas chromatographic analysis of small-scale fermentations with the transformant strains showed that, while S. cerevisiae ATF1 overexpression resulted in a substantial increase in acetate ester levels, S. cerevisiae ATF2 and K. lactis ATF overexpression only caused a moderate increase in acetate esters. This study is the first report of the presence of an ester synthesis gene in K. lactis.
authors.affiliation: Centre for Malting and Brewing Science, Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, 3001 Leuven-Heverlee, Belgium. stijn.vanlaere@student.kuleuven.be
authors.forename: Stijn D M
authors.initials: SD
authors.lastname: Van Laere
authors.forename: Sofie M G
authors.initials: SM
authors.lastname: Saerens
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Verstrepen
authors.forename: Patrick
authors.initials: P
authors.lastname: Van Dijck
authors.forename: Johan M
authors.initials: JM
authors.lastname: Thevelein
authors.forename: Freddy R
authors.initials: FR
authors.lastname: Delvaux
mesh_terms: D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000737:chemistry / Q000145:classification / Q000201:enzymology / Q000235:genetics; D004952:Esters / Q000032:analysis / Q000378:metabolism; D005285:Fermentation; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007716:Kluyveromyces / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D004952:Esters; D005656:Fungal Proteins; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; D000123:Acetyltransferases; C116217:ATF2 protein, S cerevisiae; C079238:alcohol O-acetyltransferase