Investigation of valanimycin biosynthesis

Abstract

The antibiotic valanimycin is an azoxy compound produced by Streptomyces viridifaciens MG456-hF10. Precursor incorporation experiments with (4-$\sp{13}$C) -N-(isobutylamino)serine and $\rm \lbrack\sp{15}N\sb2\rbrack$-N-(isobutylamino)serine suggest that N-(isobutylamino)serine is a specific precursor of valanimycin. Searching for enzymes related to the biosynthetic pathway of valanimycin led to the identification of valine decarboxylase and isobutylamine N-hydroxylase in crude extracts of S. viridifaciens MG456-hF10 cells. Isobutylamine N-hydroxylase requires FAD and NADH for activity. The enzyme was found to consist of two protein components. The A component of isobutylamine N-hydroxylase was partially purified and the B component was purified to homogeneity. The properties of isobutylamine N-hydroxylase were studied. Enzyme replacement experiments suggested that the A component catalyzes the reduction reaction of FAD or FMN with NADH to form FADH$\sb2$ or FMNH$\sb2,$ and that the B component catalyzes the hydroxylation reaction of isobutylamine with the aid of FADH$\sb2$ or FMNH$\sb2,$ and molecular oxygen. Attempts to clone the B component of isobutylamine N-hydroxylase were made. A library of S. viridifaciens MG456-hF10 genomic DNA was constructed using a Lambda DASH II phage vector. The library was screened with a oligonucleotide probe derived from the N-terminal protein sequence of the B component of isobutylamine N-hydroxylase. No gene fragment corresponding to the N-terminal sequence was found. Further screening will be necessary.