Nucleotide sugar donors formation

The formation of pectin and its assembly for final export across the plasmamembrane will be considered here as a production line to indicate the various limiting steps which are controlled to monitor its production. The various channels for the movement and synthesis will be described separately so that the control points can be assessed. The channels which operate for production and movement of the polymers within the cytoplasm and endomembrane system of the cells are - Channel 1. Production and movement of nucleotide sugar donors. Channel 2. Synthesis and compartmentalization of the pectin polymers within the endomembrane system. Channel 3. Movement of vesicles and fusion with the plasmamembrane for assembly and deposition within the wall. 

Figure 1. Epimerase reactions for the formation of nucleotide sugar donors.

Glycosyl esters ( sugar nucleotides ) are the glycosyl donors for the formation of wall polysaccharides. Some glycosyl-nucleotides can, in vivo, be synthesized directly from the corresponding monosaccharide, ATP, and the appropriate nucleoside triphosphate. In addition, some... 

The first member of the GT-A superfamily fold was identified in 1999 when the three-dimensional stmcture of SpsA was reported (19). This enzyme from Bacillus subtilis is involved in the formation of the spore coat and is a member of the Leloir type of GTs given its apparent use of nucleotidyl-diphospho-donor sugars as a substrate. Enzymes with the GT-A fold have an N-terminal a/p/a sandwich motif that resembles a Rossmann motif and is involved in nucleotide donor binding. Most GT-A fold enzymes also have a characteristic Asp-Xxx-Asp (DXD) or equivalent motif (EXD or TDD) near the center of the protein that coordinates to the phosphate in nucleotide donors via a divalent metal cation (Mn + or Mg +). These motifs are present in the structure of the bovine pi,4-galactosyltransferase I (5) (Fig. 4a). 

The most frequently applied concepts for the enzymatic formation of oligosaccharides and glycoproteins involve the utilization of glycosyl transferases or exo- and e do-glycosyl hydrolases (glycosidases) [58]. Glycosyl transferases require expensive and often unstable sugar nucleotides as activated donor substrates, a major problem besides the poor availability of the enzymes. However, trans-... 

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