Molecular characterization and analysis of the biosynthetic gene cluster for the azoxy antibiotic valanimycin

Streptomyces viridifaciens MG456-hF10 produces the antibiotic valanimycin, a naturally occurring azoxy compound. Valanimycin is known to be derived from valine and serine with the intermediacy of isobutylamine and isobutylhydroxylamine, but little is known about the stages in the pathway leading to the formation of the azoxy group. In previous studies, a cosmid containing S. viridifaciens DNA was isolated that conferred valanimycin production upon Streptomyces lividans TK24. Subcloning of DNA from the valanimycin-producing cosmid has led to the identification of a 22 kb segment of DNA sufficient to allow valanimycin production in S. lividans TK24. Sequencing of this DNA segment and the surrounding DNA revealed the presence of 20 genes. Gene disruption experiments defined the boundaries of the valanimycin gene cluster, which appears to contain 14 genes. The cluster includes an amino acid decarboxylase gene (vlmD), a valanimycin resistance gene (vlmF), at least two regulatory genes (vlmE, vlmI), two genes encoding a flavin monooxygenase (vlmH, vlmR), a seryl tRNA synthetase gene (vlmL) and seven genes of unknown function. Overproduction and characterization of VlmD demonstrated that it catalyses the decarboxylation of L-valine. An unusual feature of the valanimycin gene cluster is that four genes involved in branched amino acid biosynthesis are located near its 5' end.