Investigations into Viomycin Biosynthesis by Using Heterologous Production in <i>Streptomyces lividans</i>

Viomycin and capreomycin are members of the tuberactinomycin family of antituberculosis drugs. As with many antibacterial drugs, resistance to the tuberactinomycins is problematic in treating tuberculosis; this makes the development of new derivatives of these antibiotics to combat this resistance of utmost importance. To take steps towards developing new derivatives of this family of antibiotics, we have focused our efforts on understanding how these antibiotics are biosynthesized by the producing bacteria so that metabolic engineering of these pathways can be used to generate desired derivatives. Here we present the heterologous production of viomycin in Streptomyces lividans 1326 and the use of targeted-gene deletion as a mechanism for investigating viomycin biosynthesis as well as the generation of viomycin derivatives. Deletion of vioQ resulted in nonhydroxylated derivatives of viomycin, while strains lacking vioP failed to acylate the cyclic pentapeptide core of viomycin with beta-lysine. Surprisingly, strains lacking vioL produced derivatives that had the carbamoyl group of viomycin replaced by an acetyl group. Additionally, the acetylated viomycin derivatives were produced at very low levels. These two observations suggested that the carbamoyl group of the cyclic pentapeptide core of viomycin was introduced at an earlier step in the biosynthetic pathway than previously proposed. We present biochemical evidence that the carbamoyl group is added to the beta-amino group of L-2,3-diaminopropionate prior to incorporation of this amino acid by the nonribosomal peptide synthetases that form the cyclic pentapeptide cores of both viomycin and capreomycin.