title: An iterative type I polyketide synthase PKSN catalyzes synthesis of the decaketide alternapyrone with regio-specific octa-methylation.
abstract: A biosynthetic gene cluster containing five genes, alt1-5, was cloned from Alternaria solani, a causal fungus of early blight disease to tomato and potato. Homology searching indicated that the alt1, 2, and 3 genes code for cytochrome P450s and the alt4 gene for a FAD-dependent oxygenase/oxidase. The alt5 gene encodes a polyketide synthase (PKS), named PKSN, that was found to be an iterative type I complex reduced-type PKS with a C-methyltransferase domain. To identify the PKSN function, the alt5 gene was introduced into the fungal host Aspergillus oryzae under an alpha-amylase promoter. The transformant produced a polyketide compound, named alternapyrone, whose structure is shown to be 3,5-dimethyl-4-hydroxy-6-(1,3,5,7,11,13-hexamethyl-3,5,11-pentadecatrienyl)-pyran-2-one. Labeling experiments confirmed that alternapyrone is a decaketide with octa-methylation from methionine on every C(2) unit except the third unit.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. ifujii@mol.f.u-tokyo.ac.jp
authors.forename: Isao
authors.initials: I
authors.lastname: Fujii
authors.forename: Naho
authors.initials: N
authors.lastname: Yoshida
authors.forename: Shigeki
authors.initials: S
authors.lastname: Shimomaki
authors.forename: Hideaki
authors.initials: H
authors.lastname: Oikawa
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ebizuka
mesh_terms: D000528:Alternaria / Q000201:enzymology / Q000235:genetics*; D000595:Amino Acid Sequence; D001236:Aspergillus oryzae / Q000235:genetics*; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D048630:Polyketide Synthases / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014315:Triterpenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: C508257:3,5-dimethyl-4-hydroxy-6-(1,3,5,7,11,13-hexamethyl-3,5,11-pentadecatrienyl)pyran-2-one; D014315:Triterpenes; D048630:Polyketide Synthases; D008780:Methyltransferases