iso-Migrastatin, Migrastatin, and Dorrigocin Production in Streptomyces platensis NRRL 18993 Is Governed by a Single Biosynthetic Machinery Featuring an Acyltransferase-less Type I Polyketide Synthase

Abstract

iso-Migrastatin and related glutarimide-containing polyketides are potent inhibitors of tumor cell migration and their implied potential as antimetastatic agents for human cancers has garnered significant attention. Genome scanning of Streptomyces platensis NRRL 18993 unveiled two candidate gene clusters (088D and mgs); each encodes acyltransferase-less type I polyketide synthases commensurate with iso-migrastatin biosynthesis. Both clusters were inactivated by -RED-mediated PCR-targeting mutagenesis in S. platensis; iso-migrastatin production was completely abolished in the ⌬mgsF mutant SB11012 strain, whereas inactivation of 088D-orf7 yielded the SB11006 strain that exhibited no discernible change in iso-migrastatin biosynthesis. These data indicate that iso-migrastatin production is governed by the mgs cluster. Systematic gene inactivation allowed determination of the precise boundaries of the mgs cluster and the essentiality of the genes within the mgs cluster in iso-migrastatin production. The mgs cluster consists of 11 open reading frames that encode three acyltransferase-less type I polyketide synthases (MgsEFG), one discrete acyltransferase (MgsH), a type II thioesterase (MgsB), three post-PKS tailoring enzymes (MgsIJK), two glutarimide biosynthesis enzymes (MgsCD), and one regulatory protein (MgsA). A model for isomigrastatin biosynthesis is proposed based on functional assignments derived from bioinformatics and is further supported by the results of in vivo gene inactivation experiments.Cell migration is essential for invasion of the extracellular matrix and for cell dissemination during tumor metastasis (1). The glutarimide-containing polyketides iso-migrastatin (iso-MGS), 2 migrastatin (MGS), the dorrigocins (DGNs), and lactimidomycin (LTM) (Fig. 1) are potent inhibitors of human tumor cell migration and thus represent novel leads for anticancer drug discovery (2-5). Synthetic analogs of these natural products have also been investigated and found to retain potent activity despite significant structural truncation (6 -8). Retention of activity by such analogs supports the effectiveness of the privileged scaffolds highlighted by iso-MGS, MGS, LTM, and related natural products. Complementary to organic synthesis, combinatorial biosynthesis offers an alternative means of accessing natural product structural diversity. We have previously studied the biosynthetic pathway of these polyketides and shown that MGS and the DGNs are shunt metabolites of iso-MGS (9). As has been demonstrated in Streptomyces platensis NRRL 18993, one of the known iso-MGS producers, iso-MGS, MGS, and the DGNs are produced by a single biosynthetic machinery and iso-MGS undergoes H 2 O-mediated, non-enzymatic ring-expansion, and ring-opening rearrangements to afford MGS and the DGNs as shunt metabolites. We have also isolated iso-MGS congeners as minor fermentation products, produced a small library of glutarimide-containing polyketides featuring the iso-MGS, LTM, MGS, and DGN scaffolds, and found selected analogs with biological a...

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Oxazolomycin Biosynthesis in Streptomyces albus JA3453 Featuring an “Acyltransferase-less” Type I Polyketide Synthase That Incorporates Two Distinct Extender Units

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Improvement of Natamycin Production by Engineering of Phosphopantetheinyl Transferases in Streptomyces chattanoogensis L10

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