title: Identification of an enzyme system for daidzein-to-equol conversion in Slackia sp. strain NATTS.
abstract: An Escherichia coli library comprising 8,424 strains incorporating gene fragments of the equol-producing bacterium Slackia sp. strain NATTS was constructed and screened for E. coli strains having daidzein- and dihydrodaidzein (DHD)- metabolizing activity. We obtained 3 clones that functioned to convert daidzein to DHD and 2 clones that converted DHD to equol. We then sequenced the gene fragments inserted into plasmids contained by these 5 clones. All of the gene fragments were contiguous, encoding three open reading frames (ORF-1, -2, and -3). Analysis of E. coli strains containing an expression vector incorporating one of the orf-1, -2, or -3 genes revealed that (i) the protein encoded by orf-1 was involved in the conversion of cis/trans-tetrahydrodaidzein (cis/trans-THD) to equol, (ii) the protein encoded by orf-2 was involved in the conversion of DHD to cis/trans-THD, and (iii) the protein encoded by orf-3 was involved in the conversion of daidzein to DHD. ORF-1 had a primary amino acid structure similar to that of succinate dehydrogenase. ORF-2 was presumed to be an enzyme belonging to the short-chain dehydrogenase/reductase superfamily. ORF-3 was predicted to have 42% identity to the daidzein reductase of Lactococcus strain 20-92 and belonged to the NADH:flavin oxidoreductase family. These findings showed that the daidzein-to-equol conversion reaction in the Slackia sp. NATTS strain proceeds by the action of these three enzymes.
authors.affiliation: Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan. hirokazu-tsuji@yakult.co.jp
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Tsuji
authors.forename: Kaoru
authors.initials: K
authors.lastname: Moriyama
authors.forename: Koji
authors.initials: K
authors.lastname: Nomoto
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Akaza
mesh_terms: D039903:Actinobacteria / Q000201:enzymology* / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004798:Enzymes / Q000235:genetics*; D060754:Equol / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D015723:Gene Library; D007529:Isoflavones / Q000378:metabolism*; D017045:Lactococcus / Q000235:genetics; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010957:Plasmids; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D004269:DNA, Bacterial; D004798:Enzymes; D007529:Isoflavones; C433163:dihydrodaidzein; D060754:Equol; C004742:daidzein