Biosynthesis of the corallorazines, a widespread class of antibiotic cyclic lipodipeptides

Abstract

Corallorazines are cyclic lipodipeptide natural products produced by the myxobacterium <em>Corallococcus coralloides</em> B035. To decipher the basis of corallorazine biosynthesis, the corallorazine nonribosomal peptide synthetase (NRPS) biosynthetic gene cluster <em>crz</em> was identified and analyzed in detail. Here, we present a model of corallorazine biosynthesis, supported by bioinformatic analyses and <em>in vitro</em> investigations on the bimodular NRPS synthesizing the corallorazine core. Corallorazine biosynthesis shows several distinct features, such as the presence of a dehydrating condensation domain, and a unique split adenylation domain on two open reading frames. Using an alternative fatty acyl starter unit, the first steps of corallorazine biosynthesis were characterized <em>in vitro</em>, supporting our biosynthetic model. The dehydrating condensation domain was bioinformatically analyzed in detail and compared to other modifying C domains, revealing unreported specific sequence motives for this domain subfamily. Using global bioinformatics analyses, we show that the <em>crz</em> gene cluster family is widespread among bacteria and encodes notable chemical diversity. Corallorazine A displays moderate antimicrobial activity against selected Gram-positive and Gram-negative bacteria. Mode of action studies comprising whole cell analysis and <em>in vitro</em> test systems revealed that corallorazine A inhibits bacterial transcription by targeting the DNA-dependent RNA polymerase.