title: Understanding Programming of Fungal Iterative Polyketide Synthases: The Biochemical Basis for Regioselectivity by the Methyltransferase Domain in the Lovastatin Megasynthase.
abstract: Highly reducing polyketide synthases (HR-PKSs) from fungi synthesize complex natural products using a single set of domains in a highly programmed, iterative fashion. The most enigmatic feature of HR-PKSs is how tailoring domains function selectively during different iterations of chain elongation to afford structural diversity. Using the lovastatin nonaketide synthase LovB as a model system and a variety of acyl substrates, we characterized the substrate specificity of the LovB methyltransferase (MT) domain. We showed that, while the MT domain displays methylation activity toward different β-ketoacyl groups, it is exceptionally selective toward its naturally programmed β-keto-dienyltetraketide substrate with respect to both chain length and functionalization. Accompanying characterization of the ketoreductase (KR) domain displays broader substrate specificity toward different β-ketoacyl groups. Our studies indicate that selective modifications by tailoring domains, such as the MTs, are achieved by higher kinetic efficiency on a particular substrate relative to the rate of transformation by other competing domains.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Cacho
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, AB T6G 2G2, Canada.
authors.forename: Justin
authors.initials: J
authors.lastname: Thuss
authors.affiliation: Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, AB T6G 2G2, Canada.
authors.forename: Randy
authors.initials: R
authors.lastname: Sanichar
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, AB T6G 2G2, Canada.
authors.forename: Zhizeng
authors.initials: Z
authors.lastname: Gao
authors.affiliation: Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
authors.forename: Allison
authors.initials: A
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, AB T6G 2G2, Canada.
authors.forename: John C
authors.initials: JC
authors.lastname: Vederas
authors.affiliation: Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
authors.forename: Yi
authors.initials: Y
authors.lastname: Tang
mesh_terms: D005658:Fungi / Q000201:enzymology*; D008148:Lovastatin / Q000378:metabolism*; D008780:Methyltransferases / Q000378:metabolism*; D048630:Polyketide Synthases / Q000378:metabolism*
chemical_list: D048630:Polyketide Synthases; D008148:Lovastatin; D008780:Methyltransferases