Bacterial polysaccharide chains groups

Acyl groups are common in bacterial polysaccharides. The parent acids are fatty acids, hydroxy acids, and amino acids. The simplest acid, formic acid, has only been found as the amide. The occurrence of O-formyl groups had been reported, but proved to be incorrect. A-Formyl groups have been found in different polysaccharides for example, in the 0-specific side-chains of the LPS from Yersinia enlerocolitica 0 9, which are composed of 4,6-dideoxy-4-formamido-D-mannopyranosyl residues. The formyl group can assume two main conformations, s-cis (41) and s-trans (42), which are... 

Many bacterial polysaccharides contain phosphoric ester groups. There is a limited number of examples of monoesters. More common are phosphoric diesters, connecting an amino alcohol or an alditol to the polysaccharide chain. Another possibility is that oligosaccharide or oligosaccharide-alditol repeating units are connected to a polymer by phosphoric diester linkages. In addition to the intracellular teichoic acids, several bacteria, for example, different types of Streptococcus pneumoniae, elaborate extracellular polymers of this type. These polymers are generally discussed in connection with the bacterial polysaccharides. 

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. 

In the polymers of groups (1) and (2), polysaccharide chains composed of oligosaccharide repeating-units (sometimes, partially modified) are usually linked to a unique oligosaccharide unit present near the point of attachment of the chain to another polymeric chain, or to a lipid anchor. This unit is called the linkage region in the polymers of bacterial cell-wall, and the core region in lipopolysaccharides. 

Branched-chain monosaccharides have now been detected as components of bacterial polysaccharides. The known examples include yersiniose [3,6-dideoxy-4-C-(hydroxyethyl)-D-xy/o-hexose228] from Y. pseudotuberculosis, a 3-C-(hydroxymethyl)pentofuranose from Coxiella bumetti,229 and 6-deoxy-3-C-methylhexoses from the same organism and from Nitrobacter hamburgiensis.229 Several branched-chain monosaccharides were identified as components of antibiotics, and the pathways of their biosynthesis in bacteria were studied. These investigations were discussed in detail by Grisebach in this Series.230 The usual precursors for the formation of the monosaccharides of this group are the nucleoside 6-deoxyhexosyl-4-ulose diphosphates 7a and 7b. 

Preparation of modified, bacterial polysaccharides having monosaccharide analogs inserted into the polymeric chain is of interest for study of the structure-properties relationship in these biopolymers. Incorporation of chemically prepared, modified, biosynthetic precursors of the polymers in enzymic reactions seems a promising approach for achieving this aim. Such an approach, which may be termed chemical-enzymic synthesis, has now been studied by our group,439-441 using O-specific polysaccharides (10-12) of Salmonella serogroups B and E as an example. 

Bacterial polysaccharides are a very heterogeneous group and are clearly of several biosynthetic types. Many are closely equivalent to the polysaccharide (O-antigenic-type) chains of lipopolysaccharide and have presumably been released by hydrolysis, rather than transferred to lipid A or core structures. Some, such as bacterial hyaluronate, somewhat resemble wall polymers (some teichuronic acids, in this case), but have no exact counterparts. Others, such as bacterial cellulose and colominic acid (polysialic acid) are very different from... 

Curdlan is a microbial polysaccharide that occurs naturally as a linear (triple-helix) polysaccharide composed of 1,3-P-hnked D-glucose units, produced by a strain of Mcaligenes faecalis (Figure 2.38). It is a neutral, bacterial polysaccharide without branched chains. It is insoluble in water and alcohol but soluble in alkaline solution and dimethyl sulfoxide (DMSO) [274-276]. It occurs as a tasteless powder, stable in dry state. It was reported as a support matrix for enzyme immobilization, through activation with epichlorohydrin that can be covalently linked to the available amino, hydroxyl, and suHhydryl enzyme groups [277]. It has the specific character to form an irreversible gel by heating of a water suspension [278]. Its water-insoluble nature helps to improve a material s water barrier capabihty, and its solubility in... 

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