Characterization of two glycosyltransferases involved in early glycosylation steps during biosynthesis of the antitumor polyketide mithramycin by Streptomyces argillaceus

Abstract

A 2,580-bp region of the chromosome of Streptomyces argillaceus, the producer of the antitumor polyketide mithramycin, was sequenced. Analysis of the nucleotide sequence revealed the presence of two genes (mtmGIII and mtmGIV) encoding proteins that showed a high degree of similarity to glycosyltransferases involved in the biosynthesis of various antibiotics and antitumor drugs. Independent insertional inactivation of both genes produced mutants that did not synthesize mithramycin but accumulated several mithramycin intermediates. Both mutants accumulated premithramycinone, a non-glycosylated intermediate in mithramycin biosynthesis. The mutant affected in the mtmGIII gene also accumulated premithramycin A1, which contains premithramycinone as the aglycon unit and a D-olivose attached at C-12a-O. These experiments demonstrate that the glycosyltransferases MtmGIV and MtmGIII catalyze the first two glycosylation steps in mithramycin biosynthesis. A model is proposed for the glycosylation steps in mithramycin biosynthesis.

Deoxysugar Transfer during Chromomycin A 3 Biosynthesis in Streptomyces griseus subsp. griseus : New Derivatives with Antitumor Activity

“…However, CmmGI and CmmGII are excluded for this role, since mutations of the respective genes do not affect the incorporation of L-chromose B, leaving either CmmGIII or CmmGIV as candidates. Some other antibiotic gene clusters also have fewer glycosyltransferase genes than expected, for example, the mithramycin (4,8), landomycin (29), and aclacinomycin (12) gene clusters. In the latter case, it was shown that the transfer of the second and the third deoxysugar of the trisaccharide chain was carried out by the same glycosyltransferase (12).…”

Mithramycin SK modulates polyploidy and cell death in colon carcinoma cells

“…MTA and its secondary metabolite MSK were isolated and purified from the producing organisms as described previously (25,26). Stocks of MTA or MSK were prepared as 1 mmol/L solutions in sterile 150 mmol/L NaCl, maintained at -20jC, and brought to the final concentration just before use.…”

Rational Saccharide Extension by Using the Natural Product Glycosyltransferase LanGT4

“…[3,8] Increasing the length or steric bulk of the N-acyl side chain of 1 a decreases cell-surface expression of the corresponding sialic acids. [10] A rate-determining step in the de novo biosynthesis of unnatural sialic acids appears to be the phosphorylation of ManNAc at the 6-OH by ManNAc 6-kinase.…”

“…[2] Surprisingly, saccharide extension reactions have so far been investigated to only a much smaller extent, although for a number of bioactive oligosaccharide-conjugated natural products, among them mithramycin and vancomycin, extending glycosyltransferases (GTs) have been identified. [3,4] However, none of those GTs available has so far been used to elongate natural products' saccharide chains beyond the wild-type length. Here, we report the in vivo conversion of a natural-product trisaccharide into an artificial tetrasaccharide side chain.…”