Cell surface complex carbohydrates have been implicated in many physiological and pathological phenomena. The branching patterns of the N- and O-glycans are believed to be important in many of these processes. N-Glycan branching is controlled by a series of N-acetylglucosaminyltransferases (GnT) which initiate the antennae attached to the N-glycan core. GnT I, the enzyme which attaches GlcNAc in β1, 2 linkage to the Manα1-3Manβ1-4arm of the core, must act before any branching can occur. The genes for GnT I and for several other glycosyltransferases have recently been cloned in several laboratories. This work is providing evidence on how the tissue-specific and time-dependent expression of cell surface carbohydrates may be controlled.

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“Glycotechonology, ” a branch of “Biotechnology.” uses new techniques to manuplate carbohydrates or related materials for the betterment of our lives. its development is intimately related to the progress of glycobiology. These are many aspects of glycobiology that can be applied to glycotechnology. One example is to utilize carbohydrate recognition. Different animal tissues or organs have receptors specific for different sugars. Conjugation of drugs to biospecific carbohydrates can be useful for targetting of drugs to desired tissues or organs. In may cases, carbohydrate receptors strongly prefer multivalency of the carbohydrate stuructures, and thus conjugation to increase valency will results in enhanced binding. For this purpose, proteins or lipids can be modified with defined carbohydrate derivatives to form neoglycoproteins or neoglycolipids which will be specifically bound by the receptors. Alternatively, the oligosaccharides of natural glycoproteins or glycolipids can be modified or removed for the same purpose. some carbohydrates hold promises to be drugs by themselves. Analysis of primary and conformational structures of carbohydrate chains is very important in undeerstanding the biological recognition of carbohydrates, because subtle changes in conformational structures can cause enormous biological effects. This is most dramatically demonstrated by binding of two kinds of fetuin triantennary oligosaccharides by mammalian hepatic lectin. Chemically or chemoenzymatically constructed carbohydrates can be extremely useful for deciphering binding specificity as wll as to probe the effect of glycoside clustering.

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Sialidases(neuraminidases, EC 3.2.1.18) are produced in large amounts by Clostridia of the gas gangrene group and play a role in pathogenicity by supporting the degradation of mammalian tissues. Although they have different enzymic properties, their primary structures exhibit considerable similarity, indicating that all bacterial sialidases have a common origin.
Gas gangrene(clostridial myonecrosis) is a severe infection with death rates between 25 and 70%. Clostridial sialidases have been used as a target for three diagnostic tests for gas gangrene, an ELISA, an inhibition test and a fluorogenic immunoassay. A comparison of the test systems is presented. The inhibition test and the ELISA were used to analyse samples of patients with clinical signs of gas gangrene. A high degree of coincidence between immunological and bacterial analyses of the samples has been found.

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Group B Streptococci(GBS) are Gram-positive, encapsulated bacteria that cause disease in humans, especially in newborns. A major virulence determinant for GBS is the capsular polysaccharide that surrounds GBS cells. Four GBS capsular polysaccharide serotypes (Ia, Ib, II and III) are responsible for all but rare cases of GBS disease, with strains containing type III polysaccharide responsible for nearly two-thirds of all GBS infections in neonates. Mothers of infants with GBS disease have low or unmeasurable levels of antibody to the capsular polysaccharide. It is theoretically possible to increase the levels of polysaccharide-specific antibody in humans by vaccination with purified polysaccharide. However, as with many other bacterial polysaccharides, the immunogenicity of GBS polysaccharide in adults is low. Recent efforts have focused on increasing the immunogenicity of type III polysaccharide by coupling native or derivative type III oligosaccharides to tetanus toxoid. Experimental type III polysaccharide- and oligosaccharide-tetanus toxoid conjugate vaccines of different designs have been developed and their immunogenicity tested in laboratory animals. Despite differences in coupling strategies and size of polysaccharide used for conjugation, all GBS type III glycoconjugates were highly immunogenic in animals compared to uncoupled native type III polysaccharide.

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Xyloglucan is a major structural polysaccharide of the primary cell walls of higher plants. It is an extended, relatively rigid polysaccharide, with a β-(1→4)-D-glucan backbone approximately 150-1, 500nm in total contour length. Although pure xyloglucan is water-soluble, this polysaccharide may contribute to wall architecture e.g. by hydrogen-bonding to, and thus tethering, pairs of adjacent cellulosic microfibrils. Treatments, e.g. with auxin or H⁺, that promote plant cell expansion often result in in vivo xyloglucan depolymerisation. This may be partly caused by an induction of cellulase, which hydrolyses xyloglucan. In addition, however, a new xyloglucan-cleaving enzyme activity has recently been discovered—xyloglucan endotransglycosylase (XET)—which cuts a xyloglucan chain and then transfers the newly-formed (potentially reducing) terminus on to the non-reducing terminus of a neighbouring xyloglucan chain. By the action of this enzyme, intermicrofibrillar “tethers” could be broken, allowing incremental cell expansion, and then re-formed, restoring the original strength of the cell wall. The possible role of XET in wall assembly is discussed.

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