title: Functional and Structural Analysis of Programmed C-Methylation in the Biosynthesis of the Fungal Polyketide Citrinin.
abstract: Fungal polyketide synthases (PKSs) are large, multidomain enzymes that biosynthesize a wide range of natural products. A hallmark of these megasynthases is the iterative use of catalytic domains to extend and modify a series of enzyme-bound intermediates. A subset of these iterative PKSs (iPKSs) contains a C-methyltransferase (CMeT) domain that adds one or more S-adenosylmethionine (SAM)-derived methyl groups to the carbon framework. Neither the basis by which only specific positions on the growing intermediate are methylated ("programming") nor the mechanism of methylation are well understood. Domain dissection and reconstitution of PksCT, the fungal non-reducing PKS (NR-PKS) responsible for the first isolable intermediate in citrinin biosynthesis, demonstrates the role of CMeT-catalyzed methylation in precursor elongation and pentaketide formation. The crystal structure of the S-adenosyl-homocysteine (SAH) coproduct-bound PksCT CMeT domain reveals a two-subdomain organization with a novel N-terminal subdomain characteristic of PKS CMeT domains and provides insights into co-factor and ligand recognition.
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Storm
authors.affiliation: Department Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.
authors.forename: Dominik A
authors.initials: DA
authors.lastname: Herbst
authors.affiliation: Department Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland.
authors.forename: Timm
authors.initials: T
authors.lastname: Maier
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA. Electronic address: ctownse2@jhu.edu.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Townsend
mesh_terms: D001665:Binding Sites; D020134:Catalytic Domain; D002851:Chromatography, High Pressure Liquid; D002953:Citrinin / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D005658:Fungi / Q000201:enzymology*; D008745:Methylation; D062105:Molecular Docking Simulation; D032741:Monascus / Q000201:enzymology; D010802:Phylogeny; D048630:Polyketide Synthases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013379:Substrate Specificity
chemical_list: D002953:Citrinin; D048630:Polyketide Synthases; D012436:S-Adenosylmethionine
keywords: C-methylation; PKS; catalytic programming; citrinin; domain deconstruction; iterative biosynthesis; polyketide; structure