Indolocarbazoles (Glaxo Wellcome)

Actinomycetes, particularly Streptomyces, are soil microorganisms that produce diverse secondary metabolites with pharmaceutical applications, such as antibiotics and anticancer drugs. These metabolites play important roles in microbial competition and survival. This review highlights three major aspects of actinomycete secondary metabolism: (1) the biosynthesis of indolocarbazoles, (2) the biosynthesis of RiPPs (ribosomally synthesized and post-translationally modified peptides), and (3) the activation of secondary metabolism through microbial interactions. Indolocarbazoles, including staurosporine and rebeccamycin, are potent inhibitors of kinases and DNA topoisomerase I, with potential as anticancer agents. Their biosynthetic pathways involve multiple enzymatic steps, notably carbon-carbon bond formation catalyzed by cytochrome P450 enzymes. RiPPs such as goadsporin and lactazole are highly modular peptide natural products; structural gene modification enables the generation of diverse analogs. A cell-free one-pot synthesis platform has been developed for efficient analog production. To activate cryptic biosynthetic pathways, we employed a combined-culture strategy using actinomycetes and mycolic acid-containing bacteria, resulting in the discovery of 42 novel compounds. Genetic and physiological data indicate that physical contact, rather than diffusible signaling, is essential for induction. These insights emphasize the importance of microbial interactions in natural product biosynthesis and offer new directions for drug discovery through synthetic biology and microbial ecology.

Indolocarbazoles are natural products with a broad spectrum of bioactivity. A distinct feature of indolocarbazole biosynthesis is the modification of the indole and maleimide rings by regioselective tailoring enzymes. Here, we study a new indolocarbazole variant, which is encoded by the acfXODCP genes from Streptomyces venezuelae ATCC 10712. We characterise the pathway by expressing the acfXODCP genes in Streptomyces coelicolor, which led to the production of a C‐5/C‐5’‐dihydroxylated indolocarbazole, which we assign as arcyriaflavin F. We also show that a flavin‐dependent monooxygenase AcfX catalyses the C‐5/C‐5’ dihydroxylation of the unsubstituted arcyriaflavin A into arcyriaflavin F. Interestingly, AcfX shares homology to EspX from erdasporine A biosynthesis, which instead catalyses a single C‐6 indolocarbazole hydroxylation. In summary, we report a new indolocarbazole biosynthetic pathway and a regioselective C‐5 indole ring tailoring enzyme AcfX.