Abstract
Barbamide was extracted from the marine cyanobacterium Lyngbya majuscula strain 19L as a chlorinated lipopeptide for its potent molluscicidal activity. Precursor incorporation studies indicated that it is derived from acetate, l-phenylalanine, l-leucine and l-cysteine. The gene cluster responsible for biosynthesis of barbamide (bar) was cloned and characterized in this study. DNA sequence analysis of cosmid pLM49 revealed a cluster of 12 open reading frames (barA–barK) extending 26 kb including the expected polyketide synthase and non-ribosomal peptide synthetase modules and tailoring genes. The genetic architecture and domain organization of the bar cluster supports the assignment based on the apparent co-linearity of the systems. The activity assay of adenylation domains of barD (AD), barE (AE) and barG (AG2 for module 2) in an amino acid-dependent ATP-pyrophosphate exchange experiment supports the conclusion that barbamide is synthesized from acetate, l-phenylalanine, l-cysteine and l-leucine with trichloroleucine as a direct precursor by a mixed polyketide synthase/non-ribosomal polypeptide synthetase. Assembly of barbamide includes unique biochemical mechanisms for chlorination, one-carbon truncation during chain elongation, E-double bond formation and thiazole ring formation.
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