Glycan assembly

An outline of the glycan assembly method of polysaccharide synthesis. 

In the cytosol, these monosaccharides can be phosphorylated and subsequently coupled with nucleotides such as uridine diphosphate (e.g., UDP-GlcNAc), guanosine diphosphate (e.g., GDP-mannose), or cytosine monophosphate in the case of sialic acids (Fig. 2b) to create a set of high energy building blocks for glycan assembly. In some cases, such as for the initial steps... 

This section will summarize what is known about the bios)mthesis of arabinogalactan and lipoarabinomannan. For a more comprehensive discussion of how glycan assembly is coordinated, and the glycosyltransferases involved, the reader is referred to a recent review by Berg et al. [265]. 

W. J. Masterson, T. L. Doering, G. W. Hart, and P. T. Englund, A novel pathway for glycan assembly biosynthesis of the glycosyl-phosphatidylinositol anchor of the trypanosome variant surface glycoprotein, Cell., 56 (1989) 793-800. 

The strategy of using antibiotics is fairly simple. Metabolic blockade at a specific stage leads to the accumulation of intermediates at earlier points and, sometimes, to their diversion into alternative pathways. The analysis of these intermediates, and their addition to cell-free systems provides a means of deducing the individual steps in a pathway of assembly. The method is well illustrated by the long history of studies of the effects of penicillin on peptido-glycan assembly (see below). Often the exact action of an antibiotic and the nature of the pathways it affects have been elucidated simultaneously. 

This Chapter will focus on one aspect of this assembly line process the N-acetylglucosaminyltransferases which initiate the branches of complex A -glycans. The discussion will deal mainly with relatively recent work on these enzymes and the reader is referred to other sections of this book and to previous comprehensive reviews for other aspects of iV-glycan assembly [1-17]. 

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