Characterization of the Xiamenmycin Biosynthesis Gene Cluster in Streptomyces xiamenensis 318

Xiamenmycin (1) is a prenylated benzopyran derivative with anti-fibrotic activity. To investigate the genetic basis of xiamenmycin biosynthesis, we performed genome mining in the xiamenmycin-producing Streptomyces xiamenensis wild-type strain 318 to identify a candidate gene cluster. The complete gene cluster, consisting of five genes, was confirmed by a series of gene inactivations and heterologous expression. Based on bioinformatics analyses of each gene and feeding experiments, we found that the structure of an intermediate xiamenmycin B (3) accumulated in a ximA inactivation mutant, allowing us to propose a biosynthetic pathway. All five of the genes in the pathway were genetically and biochemically characterized. XimA was biochemically characterized as an ATP-dependent amide synthetase, catalyzing an amide bond formation in the presence of ATP as the final step in Xiamenmycin biosynthesis. The K (m) value of XimA was determined to be 474.38 µM for the substrate xiamenmycin B. These studies provide opportunities to use genetic and chemo-enzymatic methods to create new benzopyran derivatives as potential therapeutic agents.