Bacterial cell polysaccharide backbone

The complex structure of bacterial cell walls is discussed in Chapter 8. However, it is appropriate to mention a few bacterial polysaccharides here. The innermost layer of bacterial cell walls is a porous network of a highly crosslinked material known as pepti-doglycan or murein (see Fig. 8-29). The backbone of the peptidoglycan is a P-l,4-linked... 

Formanek has concluded from the periodicities determined from X-ray diffraction data of the bacterial cell walls that the conformation of the polysaccharide backbone should be chitin-like with a twofold helical axis [241, 242],... 

A bacterial phosphatidylinositol specific phospholipase C (PI-PLC) had been available for many years before it was demonstrated to strip a number of membrane-bound proteins from eukaryotic cell surfaces [1], Such proteins are anchored by a PI moiety in which the 6 position of inositol is glycosidically linked to glucosamine, which in turn is bonded to a polymannan backbone (Fig. 3-10). The polysaccharide chain is joined to the carboxyl terminal of the anchored protein via amide linkage to ethanolamine phosphate. The presence of a free NH2 group in the glucosamine residue makes the structure labile to nitrous acid. Bacterial PI-PLC hydrolyzes the bond between DAG and phosphati-dylinositols, releasing the water-soluble protein polysac charide-inositol phosphate moiety. These proteins are tethered by glycosylphosphatidylinositol (GPI) anchors. 

Levan has a backbone of p-(2 6) linked o-fructose and occurs as high molecular weight polysaccharide in microorganisms. It is accessible from sucrose by use of the enzyme levansucrase (sucrose 6-fructosyltransferase (FTF, EC 2.4.1.10)). Either culture broth of bacterial strains like Bacillus or Zymomonas or the cell-free supernatant can be used for the enzymatic reaction with sucrose. The molecular weight and the viscosity of levan depend on the strain used and the reaction conditions [131, 134]. Even though levan has interesting properties, it has never gained extensive industrial use up to now [134]. 

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