Search Results (3)

Streptomycetes are well-known producers of numerous bioactive secondary metabolites widely used in medicine, agriculture, and veterinary. Usually, their genomes encode 20–30 clusters for the biosynthesis of natural products. Generally, the onset and production of these compounds are tightly coordinated at multiple regulatory levels, including cluster-situated transcriptional factors. Rishirilides are biologically active type II polyketides produced by Streptomyces bottropensis. The complex regulation of rishirilides biosynthesis includes the interplay of four regulatory proteins encoded by the rsl-gene cluster: three SARP family regulators (RslR1-R3) and one MarR-type transcriptional factor (RslR4). In this work, employing gene deletion and overexpression experiments we revealed RslR1-R3 to be positive regulators of the biosynthetic pathway. Additionally, transcriptional analysis indicated that rslR2 is regulated by RslR1 and RslR3. Furthermore, RslR3 directly activates the transcription of rslR2, which stems from binding of RslR3 to the rslR2 promoter. Genetic and biochemical analyses demonstrated that RslR4 represses the transcription of the MFS transporter rslT4 and of its own gene. Moreover, DNA-binding affinity of RslR4 is strictly controlled by specific interaction with rishirilides and some of their biosynthetic precursors. Altogether, our findings revealed the intricate regulatory network of teamworking cluster-situated regulators governing the biosynthesis of rishirilides and strain self-immunity. Full article

The biological active compound rishirilide B is produced by Streptomyces bottropensis. The cosmid cos4 contains the complete rishirilide B biosynthesis gene cluster. Its heterologous expression in the host Streptomyces albus J1074 led to the production of rishirilide B as a major compound and to small amounts of rishirilide A, rishirilide D and lupinacidin A. In order to gain more insights into the biosynthesis, gene inactivation experiments and gene expression experiments were carried out. This study lays the focus on the functional elucidation of the genes involved in the early biosynthetic pathway. A total of eight genes were deleted and six gene cassettes were generated. Rishirilide production was not strongly affected by mutations in rslO2, rslO6 and rslH. The deletion of rslK4 and rslO3 led to the formation of polyketides with novel structures. These results indicated that RslK4 and RslO3 are involved in the generation or selection of the starter unit for rishirilide biosynthesis. In the rslO10 mutant strain, two novel compounds were detected, which were also produced by a strain containing solely the genes rslK1, rslK2, rslK3, rslK4, and rslA. rslO1 and rslO4 mutants predominately produce galvaquinones. Therefore, the ketoreductase RslO10 is involved in an early step of rishirilide biosynthesis and the oxygenases RslO1 and RslO4 are most probably acting on an anthracene moiety. This study led to the functional elucidation of several genes of the rishirilide pathway, including rslK4, which is involved in selecting the unusual starter unit for polyketide synthesis. Full article

Rishirilide B was isolated from Streptomyces rishiriensis and Streptomyces bottropensis on the basis of its inhibitory activity towards alpha-2-macroglobulin. The biosynthesis of rishirilide B was investigated by feeding experiments with different ¹³C labelled precursors using the heterologous host Streptomyces albus J1074::cos4 containing a cosmid encoding of the gene cluster responsible for rishirilide B production. NMR spectroscopic analysis of labelled compounds demonstrate that the tricyclic backbone of rishirilide B is a polyketide synthesized from nine acetate units. One of the acetate units is decarboxylated to give a methyl group. The origin of the starter unit was determined to be isobutyrate. Full article