Genes encoding acyl-CoA dehydrogenase (AcdH) homologues from Streptomyces coelicolor and Streptomyces avermitilis provide insights into the metabolism of small branched-chain fatty acids and macrolide antibiotic production

The cloning, using a PCR approach, of genes from both Streptomyces coelicol or and Streptomyces avermitilis encoding an acyl-CoA dehydrogenase (AcdH), putatively involved in the catabolism of branched-chain amino acids, is rep orted. The deduced amino acid sequences of both genes have a high similarit y to prokaryotic and eukaryotic short-chain acyl-CoA dehydrogenases. When t he S. coelicolor and S. avermitilis acyl-CoA dehydrogenase genes (acdH) wer e expressed in Escherichia coil, each of the AcdH flavoproteins was able to oxidize the branched-chain acyl-CoA derivatives isobutyryl-CoA, isovaleryl -CoA and cyclohexylcarbonyl-CoA, as well as the short straight-chain acyl-C oAs n-butyryl-CoA and n-valeryl-CoA in vitro. NMR spectral data confirmed t hat the oxidized product of isobutyryl-CoA is methacrylyl-CoA, which is the expected product at the acyl-CoA dehydrogenase step in the catabolism of v aline in streptomycetes. Disruption of the S. avermitilis acdH produced a m utant unable to grow on solid minimal medium containing valine, isoleucine or leucine as sole carbon sources. Feeding studies with C-13 triple-labelle d isobutyrate revealed a significant decrease in the incorporation of label into the methylmalonyl-CoA-derived positions of avermectin in the acdH mut ant. In contrast the mutation did not affect incorporation into the malonyl -CoA-derived positions of avermectin. These results are consistent with the acdH gene encoding an acyl-CoA dehydrogenase with a broad substrate specif icity that has a role in the catabolism of branched-chain amino acids in S. coelicolor and S. avermitilis.