title: FaQR, required for the biosynthesis of the strawberry flavor compound 4-hydroxy-2,5-dimethyl-3(2H)-furanone, encodes an enone oxidoreductase.
abstract: The flavor of strawberry (Fragaria x ananassa) fruit is dominated by an uncommon group of aroma compounds with a 2,5-dimethyl-3(H)-furanone structure. We report the characterization of an enzyme involved in the biosynthesis of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF; Furaneol), the key flavor compound in strawberries. Protein extracts were partially purified, and the observed distribution of enzymatic activity correlated with the presence of a single polypeptide of approximately 37 kD. Sequence analysis of two peptide fragments showed total identity with the protein sequence of a strongly ripening-induced, auxin-dependent putative quinone oxidoreductase, Fragaria x ananassa quinone oxidoreductase (FaQR). The open reading frame of the FaQR cDNA consists of 969 bp encoding a 322-amino acid protein with a calculated molecular mass of 34.3 kD. Laser capture microdissection followed by RNA extraction and amplification demonstrated the presence of FaQR mRNA in parenchyma tissue of the strawberry fruit. The FaQR protein was functionally expressed in Escherichia coli, and the monomer catalyzed the formation of HDMF. After chemical synthesis and liquid chromatography-tandem mass spectrometry analysis, 4-hydroxy-5-methyl-2-methylene-3(2H)-furanone was confirmed as a substrate of FaQR and the natural precursor of HDMF. This study demonstrates the function of the FaQR enzyme in the biosynthesis of HDMF as enone oxidoreductase and provides a foundation for the improvement of strawberry flavor and the biotechnological production of HDMF.
authors.affiliation: Institute of Pharmacy and Food Chemistry, University of Würzburg, 97074 Würzburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Raab
authors.forename: Juan Antonio
authors.initials: JA
authors.lastname: López-Ráez
authors.forename: Dorothée
authors.initials: D
authors.lastname: Klein
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Caballero
authors.forename: Enriqueta
authors.initials: E
authors.lastname: Moyano
authors.forename: Wilfried
authors.initials: W
authors.lastname: Schwab
authors.forename: Juan
authors.initials: J
authors.lastname: Muñoz-Blanco
mesh_terms: D000595:Amino Acid Sequence; D019295:Computational Biology; D017124:Conserved Sequence; D031985:Fragaria / Q000201:enzymology*; D005638:Fruit; D005663:Furans / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013649:Taste
chemical_list: D005663:Furans; D007210:Indoleacetic Acids; D010446:Peptide Fragments; D010940:Plant Proteins; D018749:RNA, Plant; C058427:furaneol; D044925:Oxidoreductases Acting on CH-CH Group Donors