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Issue 2, 2015
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A combination of polyunsaturated fatty acid, nonribosomal peptide and polyketide biosynthetic machinery is used to assemble the zeamine antibiotics

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Abstract

The zeamines are a unique group of antibiotics produced by Serratia plymuthica RVH1 that contain variable hybrid peptide–polyketide moieties connected to a common pentaamino-hydroxyalkyl chain. They exhibit potent activity against a broad spectrum of Gram-positive and Gram-negative bacteria. Here we report a combination of targeted gene deletions, high resolution LC-MS(/MS) analyses, in vitro biochemical assays and feeding studies that define the functions of several key zeamine biosynthetic enzymes. The pentaamino-hydroxyalkyl chain is assembled by an iterative multienzyme complex (Zmn10–13) that bears a close resemblance to polyunsaturated fatty acid synthases. Zmn14 was shown to function as an NADH-dependent thioester reductase and is proposed to release a tetraamino-hydroxyalkyl thioester from the acyl carrier protein domain of Zmn10 as an aldehyde. Despite the intrinsic ability of Zmn14 to catalyze further reduction of aldehydes to alcohols, the initially-formed aldehyde intermediate is proposed to undergo preferential transamination to produce zeamine II. In a parallel pathway, hexapeptide-monoketide and hexapeptide-diketide thioesters are generated by a hybrid nonribosomal peptide synthetase-polyketide synthase multienzyme complex (Zmn16–18) and subsequently conjugated to zeamine II by a stand-alone condensing enzyme (Zmn19). Structures for the resulting prezeamines were elucidated using a combination of high resolution LC-MS/MS and 1- and 2-D NMR spectroscopic analyses. The prezeamines are hypothesized to be precursors of the previously-identified zeamines, which are generated by the action of Zmn22, an acylpeptide hydrolase that specifically cleaves the N-terminal pentapeptide of the prezeamines in a post-assembly processing step. Thus, the zeamine antibiotics are assembled by a unique combination of nonribosomal peptide synthetase, type I modular polyketide synthase and polyunsaturated fatty acid synthase-like biosynthetic machinery.

Graphical abstract: A combination of polyunsaturated fatty acid, nonribosomal peptide and polyketide biosynthetic machinery is used to assemble the zeamine antibiotics

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Publication details

The article was received on 28 Jun 2014, accepted on 15 Oct 2014 and first published on 15 Oct 2014


Article type: Edge Article
DOI: 10.1039/C4SC01927J
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Citation: Chem. Sci., 2015,6, 923-929
  • Open access: Creative Commons BY-NC license
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    A combination of polyunsaturated fatty acid, nonribosomal peptide and polyketide biosynthetic machinery is used to assemble the zeamine antibiotics

    J. Masschelein, C. Clauwers, U. R. Awodi, K. Stalmans, W. Vermaelen, E. Lescrinier, A. Aertsen, C. Michiels, G. L. Challis and R. Lavigne, Chem. Sci., 2015, 6, 923
    DOI: 10.1039/C4SC01927J

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