Nucleotide Sugars

All enzymes involved in the biosynthesis of oligosaccharides can be divided into Leloir and non-Leloir pathway enzymes. While the former use nucleotide sugars as glycosyl donors, the latter use glycosyl phosphates. (Toone 1989, Wong 1994) In short the Leloir pathway can be subdivided into 4 steps.
  1. Formation of glycosyl phosphates: sugar ----(kinase)----------> sugar-1-P (Sugars of this type are use by non-Leloir pathway enzymes.)
  2. Formation of nucleotid sugars: sugar-1-P + XTP ------(nucleoside transferase / pyrophosphorylase)--------> sugar-XDP + PPi

    The activation of the monosaccharide is enthalpically driven by the energy which is released by the hydrolysis of the pyrophosphate (diphosphate) PPi.

  3. Transformation of the activated sugars to yield the eight nucleotide sugars generally used by glycosyltransferases: GDP-Man, GDP-Fuc, UDP-Gal => UDP-GalNAc, UDP-Glc => UDP-GlcNAc, UDP-Glc => UDP-GlcUA . The only exeception is CMP-Neu5Ac which is synthesized directly via the following reaction: Neu5Ac + CTP --------> CMP-Neu5Ac + PPi
  4. Transfer by glycosyltransferases.

The precursor molecule linked to Dol-P is synthesized by the stepwise addition of nucleotide sugars via the following reaction: Dol-P + XDP-sugar --------------> Dol-P-sugar + XDP

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Structure

Biosynthesis

References

VSNS-PPS course

Written by: Christian Frosch

frosch@mzdmza.zdv.uni-mainz.de

http://www.uni-mainz.de/~frosc000

Institute of Toxicology

University of Mainz

Last update: 11.07.1995