title: Biochemical and Structural Basis for Controlling Chemical Modularity in Fungal Polyketide Biosynthesis.
abstract: Modular collaboration between iterative fungal polyketide synthases (IPKSs) is an important mechanism for generating structural diversity of polyketide natural products. Inter-PKS communication and substrate channeling are controlled in large by the starter unit acyl carrier protein transacylase (SAT) domain found in the accepting IPKS module. Here, we reconstituted the modular biosynthesis of the benzaldehyde core of the chaetoviridin and chaetomugilin azaphilone natural products using the IPKSs CazF and CazM. Our studies revealed a critical role of CazM's SAT domain in selectively transferring a highly reduced triketide product from CazF. In contrast, a more oxidized triketide that is also produced by CazF and required in later stages of biosynthesis of the final product is not recognized by the SAT domain. The structural basis for the acyl unit selectivity was uncovered by the first X-ray structure of a fungal SAT domain, highlighted by a covalent hexanoyl thioester intermediate in the SAT active site. The crystal structure of SAT domain will enable protein engineering efforts aimed at mixing and matching different IPKS modules for the biosynthesis of new compounds.
authors.affiliation: †Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Jaclyn M
authors.initials: JM
authors.lastname: Winter
authors.affiliation: §Department of Energy (DOE) Institute for Genomics and Proteomics, University of California, Los Angeles, California 90095, United States.
authors.forename: Duilio
authors.initials: D
authors.lastname: Cascio
authors.affiliation: ∥Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Dietrich
authors.affiliation: ⊥Department of Pharmaceutical Sciences, University of Shizuoka, Shizuoka 422-8526, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Sato
authors.affiliation: ⊥Department of Pharmaceutical Sciences, University of Shizuoka, Shizuoka 422-8526, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: §Department of Energy (DOE) Institute for Genomics and Proteomics, University of California, Los Angeles, California 90095, United States.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sawaya
authors.affiliation: ∥Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: John C
authors.initials: JC
authors.lastname: Vederas
authors.affiliation: †Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States.|‡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: D002597:Chaetomium / Q000201:enzymology*; D008958:Models, Molecular; D048630:Polyketide Synthases / Q000737:chemistry* / Q000378:metabolism*; D061065:Polyketides / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D061065:Polyketides; D048630:Polyketide Synthases