Exploring Jadomycin Biosynthesis in Streptomyces venezuelae
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The soil bacterium Streptomyces venezuelae ISP5230 has been studied extensively for its ability to produce the jadomycin family of natural products. This family of angucyclines is distinguished by a characteristic benz[a]anthracene scaffold, the 2,6-dideoxysugar L-digitoxose, and an amino acid that is usually fused directly into the polyaromatic backbone as an oxazolone ring. The incorporation of the amino acid proceeds through a spontaneous process, which can be exploited through precursor-directed biosynthesis by altering the nitrogen source in Streptomyces venezuelae ISP5230 fermentations. Precursor-directed biosynthesis using diamino acids L-ornithine and L-lysine are described. This resulted in the successful isolation and characterization of a structurally unique eight-membered L-ornithine ring-containing jadomycin, expanding on the structural diversity permissible from this spontaneous process. This compound was further derivatized, via semi-synthetic methods, to furnish a small library of jadomycin amides containing a unique eight-membered heterocycle. The isolation and characterization of the jadomycin-like analogue L-digitoxosyl-phenanthroviridin is also discussed. Bioactivities of these structurally novel jadomycins were established and the structure activity relationship was explored between these compounds and the typical oxazolone-ring containing jadomycins. In addition, the characterization of JadX, a protein of undetermined function coded for in the jadomycin biosynthetic gene cluster is reported. The ability of JadX to bind both chloramphenicol and jadomycins and affect production of these natural products is demonstrated, suggesting a role in regulation. This work suggests JadX is a new class of “atypical” response regulator involved in the cross-regulation of disparate natural products via an end-product-mediated control mechanism. This is the first example of characterization of these “JadX-like” proteins and could shed light onto a previously unknown group of important regulatory proteins.