Conclusion

Carbohydrate research has lagged behind work done on the other two well-known macromolecules, proteins and nucleic acids. This was mostly due to the enormous variety and complexity of oligo/polysaccharide structures found in nature. With the discovery of the multiplicity of roles now assigned to carbohydrate molecules, there is an increasing need for methodologies that will allow researchers access to these structures. Organic synthetic methods are available for the production of oligosac-charides but carry disadvantages that make them difficult to apply. Enzymatic synthesis of carbohydrates is still in its infancy. Low availability of transferase enzymes and high cost of the activated sugar donor molecules make these methodologies prohibitively expensive. However, new methodologies are being developed that are focusing on two fronts: increasing the availability of glycosyltransferases and lowering the cost of cofactors. Finally, whole-cell systems are being developed that address both of these targets. These do not require the purification of the enzymes or the input of costly sugar donor molecules, and they can produce desired oligo-saccharides in high quantity. Besides the functions they serve in the natural environment, novel applications are being sought for carbohydrates. Oligosaccharide moieties are used as vaccines in prevention of variety of microbial infections. Recently, new polysaccharide conjugate vaccines have been developed [71]. Polysaccharides have been discovered to have antibacterial properties. One such example is the modified disaccharide moiety of vancomycin, which alone exhibits novel antibacterial

Figure 5 The production systems for globotriose (Gala1,4Lac) [69] and N-acetyllactosamine [70] as designed by researchers at the Tokyo Research Laboratories, Kyowa Hakko Kogyo Co. Ltd. Both IgtB and IgtC were from Neisseria gonorrhoeae.
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