Covalent CouN7 enzyme intermediate for acyl group shuttling in aminocoumarin biosynthesis

Five gene products are required for assembly of the central pyrrole moiety of coumermycin A1

Coumermycin A1 is an aminocoumarin antibiotic produced by Streptomyces rishiriensis. It exhibits potent antibacterial and anticancer activity. The coumermycin A1 molecule contains two terminal 5-methyl-pyrrole-2-carboxylic acid moieties and one central 3-methylpyrrole-2,4-dicarboxylic acid moiety (CPM). While the biosynthesis of the terminal moieties has been elucidated in detail, the pathway leading to the CPM remains poorly understood. In this work, the minimal set of genes required for the generation of the CPM scaffold was identified. It comprises the five genes couR1, couR2a, couR2b, couR3, and couR4 which are grouped together in a contiguous 4.7 kb region within the coumermycin A1 biosynthetic gene cluster. The DNA fragment containing these genes was cloned into an expression plasmid and heterologously expressed in Streptomyces coelicolor M1146. Thereupon, the formation of CPM could be shown by HPLC and by HPLC-MS/MS, in comparison to an authentic CPM standard. This proves that the genes couR1–couR4 are sufficient to direct the biosynthesis of CPM, and that the adjacent genes couR5 and couR6 are not required for this pathway. The enzyme CouR3 was expressed in Escherichia coli and purified to near homogeneity. The protein exhibited an ATPase activity similar to that reported for its close ortholog, the threonine kinase PduX. However, we could not show a threonine kinase activity of CouR3, and; therefore, the substrate of CouR3 in CPM biosynthesis is still unknown and may be different from threonine.

Characterization of TioQ, a type II thioesterase from the thiocoraline biosynthetic cluster

An antitumor agent thiocoraline is a thiodepsipeptide marine product derived from two Micromonospora sp. strains that inhibits protein synthesis by binding of its key 3-hydroxyquinaldic acid (3HQA) chromophores to duplex DNA. There are at least two potential pathways via which the 3HQA moiety could be biosynthesized from L-Trp. By biochemical characterization and by preparation of knockouts of an adenylation-thiolation enzyme, TioK, and of two type II thioesterases, TioP and TioQ, found in the thiocoraline biosynthetic gene cluster, we gained valuable insight into the pathway followed for the production of 3HQA.

Genetic engineering of antibiotic biosynthesis for the generation of new aminocoumarins

The aminocoumarin antibiotics novobiocin, clorobiocin and coumermycin A(1) are inhibitors of gyrase and highly effective antibacterial agents. Their biosynthetic gene clusters have been cloned from the respective Streptomyces producer strains, and the function of nearly all genes contained therein has been elucidated by genetic and biochemical methods. Efficient methods have been developed for the genetic manipulation and the heterologous expression of the clusters, and more than 100 new derivatives of these antibiotics have been generated by metabolic engineering, mutasynthesis and chemoenzymatic synthesis, providing a model for the power of genetic and genomic methods for the generation of new bioactive compounds.

Optimizing glycosyltransferase specificity via "hot spot" saturation mutagenesis presents a catalyst for novobiocin glycorandomization

A comprehensive two-phase "hot spot" saturation mutagenesis strategy for the rapid evolution of glycosyltransferase (GT) specificity for nonnatural acceptors is described. Specifically, the application of a high-throughput screen (based on the fluorescent acceptor umbelliferone) was used to identify key amino acid hot spots that contribute to GT proficiency and/or promiscuity. Saturation mutagenesis of the corresponding hot spots facilitated the utilization of a lower-throughput screen to provide OleD prodigy capable of efficiently glycosylating the nonnatural acceptor novobiocic acid with an array of unique sugars. Incredibly, even in the absence of a high-throughput screen for novobiocic acid glycosylation, this approach rapidly led to improvements in the desired catalytic activity of several hundred-fold.