Abstract:Summary
Streptomyces sp. NTK937, producer of benzoxazole antibiotic caboxamycin, produces in addition a methyl ester derivative, O‐methylcaboxamycin. Caboxamycin cluster, comprising one regulatory and nine structural genes, has been delimited, and each gene has been individually inactivated to demonstrate its role in the biosynthetic process. The O‐methyltransferase potentially responsible for O‐methylcaboxamycin synthesis would reside outside this cluster. Five of the genes, cbxR, cbxA, cbxB, cbxD and cbxE, e… Show more
“…sp. NTK 937), have been identified (Figure c) . Sequence analysis failed to identify any homologue to the enzymes in RiPPs or NRPs or an N‐type ATP pyrophosphohydrolase.…”
Section: Introductionmentioning
confidence: 99%
“…This amide is then rearranged by the intramolecular attack of a hydroxyl and ring closure catalyzed by BomN (putative amidohydrolase) (Figure d). Since the gene clusters for nataxazole and caboxamycin all contain the homologue of the bomN amidohydrolase, the synthesis of the benzoxazole is expected to be the same in each case …”
Heterocycles, a class of molecules that includes oxazoles, constitute one of the most common building blocks in current pharmaceuticals and are common in medicinally important natural products. The antitumor natural product nataxazole is a model for a large class of benzoxazole‐containing molecules that are made by a pathway that is not characterized. We report structural, biochemical, and chemical evidence that benzoxazole biosynthesis proceeds through an ester generated by an ATP‐dependent adenylating enzyme. The ester rearranges via a tetrahedral hemiorthoamide to yield an amide, which is a shunt product and not, as previously thought, an intermediate in the pathway. A second zinc‐dependent enzyme catalyzes the formation of hemiorthoamide from the ester but, by shuttling protons, the enzyme eliminates water, a reverse hydrolysis reaction, to yield the benzoxazole and avoids the amide. These insights have allowed us to harness the pathway to synthesize a series of novel halogenated benzoxazoles.
“…sp. NTK 937), have been identified (Figure c) . Sequence analysis failed to identify any homologue to the enzymes in RiPPs or NRPs or an N‐type ATP pyrophosphohydrolase.…”
Section: Introductionmentioning
confidence: 99%
“…This amide is then rearranged by the intramolecular attack of a hydroxyl and ring closure catalyzed by BomN (putative amidohydrolase) (Figure d). Since the gene clusters for nataxazole and caboxamycin all contain the homologue of the bomN amidohydrolase, the synthesis of the benzoxazole is expected to be the same in each case …”
Heterocycles, a class of molecules that includes oxazoles, constitute one of the most common building blocks in current pharmaceuticals and are common in medicinally important natural products. The antitumor natural product nataxazole is a model for a large class of benzoxazole‐containing molecules that are made by a pathway that is not characterized. We report structural, biochemical, and chemical evidence that benzoxazole biosynthesis proceeds through an ester generated by an ATP‐dependent adenylating enzyme. The ester rearranges via a tetrahedral hemiorthoamide to yield an amide, which is a shunt product and not, as previously thought, an intermediate in the pathway. A second zinc‐dependent enzyme catalyzes the formation of hemiorthoamide from the ester but, by shuttling protons, the enzyme eliminates water, a reverse hydrolysis reaction, to yield the benzoxazole and avoids the amide. These insights have allowed us to harness the pathway to synthesize a series of novel halogenated benzoxazoles.
“…We also sought to improve mutasynthesis yields by ectopic expression of regulatory gene cbxR in the strain ΔcbxA/ΔentC. However, production levels did not increase accordingly as in prior uses of cbxR [13], possibly due to the lack of cbxA , which might contain the effecting region for CbxR, given the structural organization of the biosynthetic cluster.Fig. 6Schematic representation of the biosynthetic origin of compounds 1 – 19
…”
Section: Discussionmentioning
confidence: 99%
“…Furthermore, upon gene replacement of the salicylate synthase cbxA , a third compound was observed, 3′-hydroxycaboxamycin ( 3 ) (Fig. 1b), stemming from the cross-talk between the caboxamycin biosynthesis pathway and 2,3-dihydroxybenzoate (DHB) generated in the biosynthetic pathway for the siderophore enterobactin [13]. This phenomenon, together with our previous studies of the nataxazole biosynthetic cluster, where we identified cross-talk between the nataxazole and coelibactin biosynthesis pathways that led to biosynthesis of benzoxazole UK-1 [7, 8], sparked our interest for the generation of novel benzoxazoles exploring the biocombinatorial potential of these family of compounds.Fig.…”
BackgroundThe biosynthesis pathway of benzoxazole compounds caboxamycin and nataxazole have been recently elucidated. Both compounds share one of their precursors, 3-hydroxyanthranilate (two units in the case of nataxazole). In addition, caboxamycin structure includes a salicylate moiety while 6-methylsalycilate is the third scaffold in nataxazole. Pathways cross-talk has been identified in caboxamycin producer Streptomyces sp. NTK937, between caboxamycin and enterobactin pathways, and nataxazole producer Streptomyces sp. Tü6176, between nataxazole and coelibactin pathways. These events represent a natural form of combinatorial biosynthesis.ResultsEleven novel caboxamycin derivatives, and five putative novel derivatives, bearing distinct substitutions in the aryl ring have been generated. These compounds were produced by heterologous expression of several caboxamycin biosynthesis genes in Streptomyces albus J1074 (two compounds), by combinatorial biosynthesis in Streptomyces sp. NTK937 expressing nataxazole iterative polyketide synthase (two compounds) and by mutasynthesis using a nonproducing mutant of Streptomyces sp. NTK937 (12 compounds). Some of the compounds showed improved bioactive properties in comparison with caboxamycin.ConclusionsIn addition to the benzoxazoles naturally biosynthesized by the caboxamycin and nataxazole producers, a greater structural diversity can be generated by mutasynthesis and heterologous expression of benzoxazole biosynthesis genes, not only in the respective producer strains but also in non-benzoxazole producers such as S. albus strains. These results show that the production of a wide variety of benzoxazoles could be potentially achieved by the sole expression of cbxBCDE genes (or orthologs thereof), supplying an external source of salicylate-like compounds, or with the concomitant expression of other genes capable of synthesizing salicylates, such as cbxA or natPK.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-017-0709-6) contains supplementary material, which is available to authorized users.
Jomthonic acids (JAs) are a group of natural products (NPs) with adipogenic activity. Structurally, JAs are formed by a modified β-methylphenylalanine residue, whose biosynthesis involves a methyltransferase that in Streptomyces hygroscopicus has been identified as MppJ. Up to date, three JA members (A–C) and a few other natural products containing β-methylphenylalanine have been discovered from soil-derived microorganisms. Herein, we report the identification of a gene (jomM) coding for a putative methyltransferase highly identical to MppJ in the chromosome of the marine actinobacteria Streptomyces caniferus GUA-06-05-006A. In its 5’ region, jomM clusters with two polyketide synthases (PKS) (jomP1, jomP2), a nonribosomal peptide synthetase (NRPS) (jomN) and a thioesterase gene (jomT), possibly conforming a single transcriptional unit. Insertion of a strong constitutive promoter upstream of jomP1 led to the detection of JA A, along with at least two novel JA family members (D and E). Independent inactivation of jomP1, jomN and jomM abolished production of JA A, JA D and JA E, indicating the involvement of these genes in JA biosynthesis. Heterologous expression of the JA biosynthesis cluster in Streptomyces coelicolor M1152 and in Streptomyces albus J1074 led to the production of JA A, B, C and F. We propose a pathway for JAs biosynthesis based on the findings here described.
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