The biosynthetic mta gene cluster responsible for myxothiazol formation from the fruiting body forming myxobacterium Stigmatella aurantiaca DW4/3-1 was sequenced and analyzed. Myxothiazol, an inhibitor of the electron transport via the bc 1 -complex of the respiratory chain, is biosynthesized by a unique combination of several polyketide synthases (PKS) and nonribosomal peptide synthetases (NRPS), which are activated by the 4-phosphopantetheinyl transferase MtaA. Genomic replacement of a fragment of mtaB and insertion of a kanamycin resistance gene into mtaA both impaired myxothiazol synthesis. Genes mtaC and mtaD encode the enzymes for bis-thiazol(ine) formation and chain extension on one pure NRPS (MtaC) and on a unique combination of PKS and NRPS (MtaD). The genes mtaE and mtaF encode PKSs including peptide fragments with homology to methyltransferases. These methyltransferase modules are assumed to be necessary for the formation of the proposed methoxy-and -methoxy-acrylate intermediates of myxothiazol biosynthesis. The last gene of the cluster, mtaG, again resembles a NRPS and provides insight into the mechanism of the formation of the terminal amide of myxothiazol. The carbon backbone of an amino acid added to the myxothiazolacid is assumed to be removed via an unprecedented module with homology to monooxygenases within MtaG.Myxobacteria are Gram-negative soil bacteria that are assigned to the two suborders Cystobacterineae and Sorangineae. Both belong to the ␦-group of the Proteobacteria (1). They are distinguished from most other bacteria by their ability to glide in swarms, to feed cooperatively, and to form fruiting bodies upon starvation (2, 3). In addition, they have been shown to produce a wide variety of secondary metabolites with unique structures and biological activities (for reviews, see Refs. 4 and 5). These include the electron transport inhibitors myxothiazol (6), stigmatellin (7), and myxalamids (5, 8) produced by different strains of Stigmatella aurantiaca (Cystobacterineae) and the epothilones produced by Sorangium cellulosum (Sorangineae) (9) (structures are given in Fig. 1). Due to their antitumor activity, epothilones have attracted great attention (10 -12). Myxothiazol as well as epothilones contain a thiazole ring that is formed by the incorporation of cysteine into the polyketide backbone (13). Thiazoline and thiazolidine structures of bacitracin in Bacillus licheniformis (14) and the bacterial siderophores yersiniabactin and mycobactin have recently been shown to be biosynthesized by a NRPS 1 or a combined PKS/NRPS in Yersinia pestis and Mycobacterium tuberculosis (15)(16)(17) . 22)). No such combinations have been published so far for the formation of a thiazole coupled to a polyketide structure. In addition to the bis-thiazole moiety, myxothiazol has some unique features: the unusual leucine derived starter unit 3-methyl-butyryl-CoA (13) and the linear polyketide backbone, which includes a -methoxy-acrylate and a terminal amide structure.Little is known about the biochemistry o...
PKSs and amino acids in NRPSs. These precursors are 2 Institut fu ¨r Pharmazeutische Biologie attached as thioesters to carrier proteins via a phospho-Mendelssohnstr. 1 pantetheinyl arm that needs to be transferred posttrans-Technische Universita ¨t lationally to conserved serine residues in each carrier 38106 Braunschweig protein [4]. The selection for each monomer is performed Germany by acyl transferase domains (AT domains in PKS) and 3 University of Washington adenylation domains (A domains in NRPS). After loading Department of Chemistry of the megasynthetase, the condensation reactions be-Seattle, Washington 98195 tween the monomers are catalyzed by ketosynthase (KS) domains in PKS and by condensation (C) domains in NRPS, which leads to the formation of carbon-carbon bonds by Claisen ester condensation and to peptide Summary linkages, respectively. During the last few years, hybrid systems employing A DNA region of 41.847 base pairs from Melittangium PKS and NRPS biochemistry in the course of the assemlichenicola Me l46 is shown to be responsible for the bly of one product have been reported [5-7], which rebiosynthesis of the potent electron transport inhibitor sulted in intensified studies aimed at the combination melithiazol. Melithiazol is formed by a combined polyof PKS/NRPS assembly lines for combinatorial biosynketide synthase/peptide synthetase system resembling thesis [8-10]. the myxothiazol megasynthetase from Stigmatella Although relatively rarely studied in comparison to aurantiaca DW4/3-1. Both natural products share an actinomycetes, myxobacteria have been shown to be a almost identical core region but employ different starter major source of secondary metabolites, especially those molecules. Additionally, melithiazol contains a terminal methyl ester instead of the amide moiety found that show the typical features of PKS/NRPS hybrids: the in myxothiazol. Similar to myxothiazol formation, the incorporation of amino acids and short chain carboxylic methyl ester is formed via an amide intermediate, which acids into their backbones [11]. Cloning of the responsiis converted by a hydrolase and an unusual type of ble genes revealed biosynthetic enzymes that harbor SAM (S-adenosyl-L-methionine)-dependent methyl-PKS and NRPS modules, even present on one single transferase into the methyl ester. When transferred open reading frame [12, 13], and a variety of other novel into the myxothiazol A (amide) producer, these two features have been described from multimodular myxogenes lead to the formation of the methyl ester of bacterial systems [14-19]. Cyanobacteria seem to be myxothiazol. The methyl transferase described is a equally rich in "nonstandard" biosynthetic systems, as member of a protein subfamily of a previously unhas been shown in recent genetic studies [20-22]. known function lacking a typical SAM binding motif. Myxothiazol [23, 24] and melithiazol [25, 26] represent two highly efficient electron transport inhibitors of the eukaryotic respiratory chain which are produced by the
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.