title: A single module type I polyketide synthase directs de novo macrolactone biogenesis during galbonolide biosynthesis in Streptomyces galbus.
abstract: Galbonolide (GAL) A and B are antifungal macrolactone polyketides produced by Streptomyces galbus. During their polyketide chain assembly, GAL-A and -B incorporate methoxymalonate and methylmalonate, respectively, in the fourth chain extension step. The methoxymalonyl-acyl carrier protein biosynthesis locus (galG to K) is specifically involved in GAL-A biosynthesis, and this locus is neighbored by a gene cluster composed of galA-E. GalA-C constitute a single module, highly reducing type I polyketide synthase (PKS). GalD and GalE are cytochrome P450 and Rieske domain protein, respectively. Gene knock-out experiments verified that galB, -C, and -D are essential for GAL biosynthesis. A galD mutant accumulated a GAL-C that lacked two hydroxyl groups and a double bond when compared with GAL-B. A [U-(13)C]propionate feeding experiment indicated that no rare precursor other than methoxymalonate was incorporated during GAL biogenesis. A search of the S. galbus genome for a modular type I PKS system, the type that was expected to direct GAL biosynthesis, resulted in the identification of only one modular type I PKS gene cluster. Homology analysis indicated that this PKS gene cluster is the locus for vicenistatin biosynthesis. This cluster was previously reported in Streptomyces halstedii. A gene deletion of the vinP2 ortholog clearly demonstrated that this modular type I PKS system is not involved in GAL biosynthesis. Therefore, we propose that GalA-C direct macrolactone polyketide formation for GAL. Our studies provide a glimpse into a novel biochemical strategy used for polyketide synthesis; that is, the iterative assembly of propionates with highly programmed β-keto group modifications.
authors.affiliation: From the Department of Biological Science, Myongji University, Yongin 449-728.
authors.forename: Hyun-Ju
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: From the Department of Biological Science, Myongji University, Yongin 449-728.
authors.forename: Suman
authors.initials: S
authors.lastname: Karki
authors.affiliation: From the Department of Biological Science, Myongji University, Yongin 449-728.
authors.forename: So-Yeon
authors.initials: SY
authors.lastname: Kwon
authors.affiliation: the Department of Oriental Medicine Resources, Mokpo National University, Muan 534-729, and.
authors.forename: Si-Hyung
authors.initials: SH
authors.lastname: Park
authors.affiliation: From the Department of Biological Science, Myongji University, Yongin 449-728, GreenGene BioTech Inc., Yongin 449-728, Republic of Korea.
authors.forename: Baek-Hie
authors.initials: BH
authors.lastname: Nahm
authors.affiliation: GreenGene BioTech Inc., Yongin 449-728, Republic of Korea.
authors.forename: Yeon-Ki
authors.initials: YK
authors.lastname: Kim
authors.affiliation: From the Department of Biological Science, Myongji University, Yongin 449-728, hjink@mju.ac.kr.
authors.forename: Hyung-Jin
authors.initials: HJ
authors.lastname: Kwon
mesh_terms: D020868:Gene Silencing; D007783:Lactones / Q000378:metabolism; D005810:Multigene Family / Q000235:genetics; D048630:Polyketide Synthases / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011422:Propionates / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D007783:Lactones; D011422:Propionates; C047784:rustmicin; D048630:Polyketide Synthases
keywords: Actinobacteria; Bacterial Genetics; Galbonolide; Gene Knockout; Highly Reducing Type I Polyketide Synthase; Natural Product Biosynthesis; Polyketide; Streptomyces galbus