landomycin-a and tetrangulol

The functional roles of all proposed enzymes involved in the post-PKS redox reactions of the biosynthesis of various landomycin aglycones were thoroughly studied, both in vivo and in vitro. The results revealed that LanM2 acts as a dehydratase and is responsible for concomitant release of the last PKS-tethered intermediate to yield prejadomycin (10). Prejadomycin (10) was confirmed to be a general pathway intermediate of the biosynthesis. Oxygenase LanE and the reductase LanV are sufficient to convert 10 into 11-deoxylandomycinone (5) in the presence of NADH. LanZ4 is a reductase providing reduced flavin (FMNH) co-factor to the partner enzyme LanZ5, which controls all remaining steps. LanZ5, a bifunctional oxygenase-dehydratase, is a key enzyme directing landomycin biosynthesis. It catalyzes hydroxylation at the 11-position preferentially only after the first glycosylation step, and requires the presence of LanZ4. In the absence of such a glycosylation, LanZ5 catalyzes C5,6-dehydration, leading to the production of anhydrolandomycinone (8) or tetrangulol (9). The overall results provided a revised pathway for the biosynthesis of the four aglycones that are found in various congeners of the landomycin group.

Topics: Aminoglycosides; Bacterial Proteins; Benz(a)Anthracenes; Cloning, Molecular; Escherichia coli; Hydro-Lyases; Isoquinolines; NAD; Naphthoquinones; Oligosaccharides; Oxidation-Reduction; Oxidoreductases; Oxygenases; Polyketide Synthases; Recombinant Proteins; Streptomyces

The glycosyltransferase LanGT2 is involved in the biosynthesis of the hexasaccharide side chain of the angucyclic antibiotic landomycin A. Its function was elucidated by targeted gene inactivation of lanGT2. The main metabolite of the obtained mutant was identified as tetrangulol (4), the progenitor of the landomycin aglycon (7). The lack of the sugar side chain indicates that LanGT2 catalyzes the priming glycosyl transfer in the hexasaccharide biosynthesis: the attachment of a D-olivose to O-8 of the polyketide backbone. Heterologous expression of urdGT2 from S. fradiae Tü2717 in this mutant resulted in the production of a novel C-glycosylated angucycline (6).

Topics: Aminoglycosides; Benz(a)Anthracenes; Catalysis; Deoxy Sugars; Enzyme Activation; Glycosylation; Glycosyltransferases; Molecular Structure; Mutation; Streptomyces