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A transglutaminase homologue as a condensation catalyst in antibiotic assembly lines

Abstract

The unrelenting emergence of antibiotic-resistant bacterial pathogens demands the investigation of antibiotics with new modes of action. The pseudopeptide antibiotic andrimid is a nanomolar inhibitor of the bacterial acetyl-CoA carboxylase that catalyses the first committed step in prokaryotic fatty acid biosynthesis1. Recently, the andrimid (adm) biosynthetic gene cluster was isolated and heterologously expressed in Escherichia coli2. This establishes a heterologous biological host in which to rapidly probe features of andrimid formation and to use biosynthetic engineering to make unnatural variants of this important and promising new class of antibiotics. Bioinformatic analysis of the adm cluster revealed a dissociated biosynthetic assembly system lacking canonical amide synthases between the first three carrier protein domains. Here we report that AdmF, a transglutaminase (TGase) homologue, catalyses the formation of the first amide bond, an N-acyl-β-peptide link, in andrimid biosynthesis. Hence, AdmF is a newly discovered biosynthetic enzyme that acts as a stand-alone amide synthase between protein-bound, thiotemplated substrates in an antibiotic enzymatic assembly line. TGases (enzyme class (EC) 2.3.2.13) normally catalyse the cross-linking of (poly)peptides by creating isopeptidic bonds between the γ-carboxamide group of a glutamine side chain of one protein and various amine donors, including lysine side chains3. To the best of our knowledge, the present study constitutes the first report of a TGase-like enzyme recruited for the assembly of an antibiotic. Moreover, genome mining using the AdmF sequence yielded additional TGases in unassigned natural product biosynthetic pathways. With many more microbial genomes being sequenced, such a strategy could potentially unearth biosynthetic pathways producing new classes of antibiotics.

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Figure 1: First condensation step in andrimid biosynthesis.
Figure 2: Analysis of the AdmF-catalysed condensation of octatrienoyl to β-phenylalanine.
Figure 3: Proposed mechanism of AdmF compared with prototypical ketosynthase (KS) domains in PKS and condensation (C) domains in NRPS.

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Acknowledgements

We thank J. Clardy for providing cosmid 2194C1 and M. Fischbach for helpful discussions. This work was supported in part by the NIH.

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Correspondence to Christopher T. Walsh.

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Fortin, P., Walsh, C. & Magarvey, N. A transglutaminase homologue as a condensation catalyst in antibiotic assembly lines. Nature 448, 824–827 (2007). https://doi.org/10.1038/nature06068

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