On the basis of these resemblances, putative functional assignments of the products of most of the newly discovered ORFs were made, including those of genes involved in the PKS and tailoring steps in the biosynthesis of the granaticin aglycone, steps in the deoxy sugar pathway, and putative regulatory and export functions.

Medermycin is a Streptomyces aromatic C-glycoside antibiotic classified in the benzoisochromanequinones (BIQs), which presents several interesting biosynthetic problems concerning polyketide synthase (PKS), post-PKS tailoring and deoxysugar pathways. The biosynthetic gene cluster for medermycin (the med cluster) was cloned from Streptomyces sp. AM-7161. Completeness of the clone was proved by the heterologous expression of a cosmid carrying the entire med cluster in Streptomyces coelicolor CH999 to produce medermycin. The DNA sequence of the cosmid (36 202 bp) revealed 34 complete ORFs, with an incomplete ORF at either end. Functional assignment of the deduced products was made for PKS and biosynthetically related enzymes, tailoring steps including strereochemical control, oxidation, angolosamine pathway, C-glycosylation, and regulation. The med cluster was estimated to be about 30 kb long, covering 29 ORFs. An unusual characteristic of the cluster is the disconnected organization of the minimal PKS genes: med-ORF23 encoding the acyl carrier protein is 20 kb apart from med-ORF1 and med-ORF2 for the two ketosynthase components. Secondly, the six genes (med-ORF14, 15, 16, 17, 18 and 20) for the biosynthesis of the deoxysugar, angolosamine, are all contiguous. Finally, the finding of a glycosyltransferase gene, med-ORF8, suggests a possible involvement of conventional C-glycosylation in medermycin biosynthesis. Comparison among the three complete BIQ gene clusters – med and those for actinorhodin (act) and granaticin (gra) – revealed some common genes whose deduced functions are unavailable from database searches (the ‘unknowns’). An example is med-ORF5, a homologue of actVI-ORF3 and gra-ORF18, which was highlighted by a recent proteomic analysis of S. coelicolor A3(2).

Analysis of deoxysugar biosynthetic genes of the urdamycin biosynthetic gene cluster revealed a widely common biosynthetic pathway leading to D-olivose and L-rhodinose. Several enzymes responsible for specific steps of this pathway could be assigned. The pathway had to be modified compared to earlier suggestions. Two glycosyltransferases normally involved in the C-glycosyltransfer of D-olivose at the 9-position (UrdGT2) and in conversion of 100-2 to urdamycin G (UrdGT1c) show relaxed substrate specificity for their activated deoxysugar co-substrate and their alcohol substrate, respectively. They can transfer activated D-rhodinose (instead of D-olivose) to the 9-position, and attach L-rhodinose to the 4A-position normally occupied by a D-olivose unit, respectively.

No abstract

The actVl genetic region ofStreptomyces coelicolor A3(2) is part of the biosynthetic gene cluster of actinorhodin (ACT), the act cluster, consisting of six ORFs: ORFB, ORFA, ORF1, ORF2, ORF3, ORF4. A newly devised method of ACTdetection with a combination of HPLC and LC/MSwas applied to the analysis of the disruptants of each OREACTwas produced by those of ORFB, ORFA, ORF3, and ORF4. Instead of ACT, the ORF1disruptant produced 3,8-dihydroxy-l -methylanthraquinone-2-carboxylic acid (DMAC)and aloesaponarin II as shunt products. The ORF2 disruptant gave 4-dihydro-9-hydroxy-l -methyl-1 0-oxo-3-//-naphtho-[2,3- pp.144 -152

No abstract

Sweet success: A natural product glycosyltransferase, UrdGT2 from Streptomyces fradiae Tü2717, is the first glycosyltransferase able to catalyze both C‐glycosidic and O‐glycosidic sugar transfers. These results shed new light on the mechanisms of C‐glycosylation of aromatic compounds, which is significant for chemoenzymatic drug lead derivatization as well as for enzymology.

UrdGT2 is a d-olivosyltransferase from the metabolic pathway of urdamycin A, an angucycline antitumor and antimicrobial drug. The remarkable feature of this biocatalyst is its ability to set up C-glycosidic bonds. Using an in vivo system suitable to deliver the trideoxysugar rhodinose in both d- and l- configuration we could verify that both have been accepted as substrates and attached to the urdamycin polyketide backbone via a C-glycosidic bond. Regardless of the stereochemistry, these C-glycosides served as acceptor for a subsequent glycosylation step to yield the novel urdamycins R and S with di-rhodinosyl side chains at C-9 of the polyketide moiety.