Oligosaccharide metabolically engineered cells

Table 5.3 Production of oligosaccharides by metabolic engineered living E. coli cells (see Scheme 5.9 for product formulas).

Scheme 5.9 Examples of oligosaccharides produced by metabolically engineered living E. coli cells (see Table 5.3 for references). Lacto-N-neotetraose (LNnT, 17), globotetraose (18), Le trisaccharide bound on a GicNAc motif (19),...

Ruffing A, Chen RR. Metabolic engineering of microbes for oligosaccharide and polysaccharide synthesis. Microb. Cell Eact. 2006 5 25. 

Figure 7 Metabolic oligosaccharide engineering of sialic acid. Exogenously supplied analogs of ManNAc or sialic acid can intercept the sialic acid biosynthetic pathway (at different points) and be displayed on the cell surface in place of the natural sialic acids NeuSAc and Neu5Gc. The sampling of non-natural "R" groups shown here was selected from References 84, 92, 93 and 97-101 (note that not all "mix-and-match" permutations of the indicated groups have been reported). Additional information on the enzymes shown can be found in the KEGG databases (see the Legend for Fig. 3).

Sampathkumar S-G, Li AV, Jones MB, Sun Z, Yarema KJ. Metabolic installation of thiols into sialic acid modulates adhesion and stem cell biology. Nat. Chem. Biol. 2006 2 149-152. Mahal LK, Yarema KJ, Bertozzi CR. Engineering chemical reactivity on cell surfaces through oligosaccharide biosynthesis. Science 1997 276 1125-1128. 

We begin with an overview of the structures of glycoconjugates on cell surfaces (for more comprehensive reviews, see Refs. 2, 12-14, and 24). Next, the pathways of monosaccharide interconversions inside the cell are smnmarized, providing a framework for opportunities in unnatural monosaccharide metabolism. Specihc examples of modihed sugars and their effects on cells are then presented. Finally, the biosynthetic pathway of sialic acid is discussed with respect to its utility for cell surface oligosaccharide engineering. 

Figure 2 Metabolic substrate engineering as a strategy for modulating cell surface oligosaccharide structure. Modified metabolic substrates can intercept a biosynthetic pathway in two ways the pathway might be inhibited, leading to truncated structures on the cell surface, or the modified substrate might be incorporated into oligosaccharides in place of the normal substrate.

Some early attempts at metabolic oligosaccharide engineering using haloge-nated and deoxy sugars resulted in cell death. In retrospect, we now know that some of these compounds are inhibitory of intracellular biosynthetic pathways [37,38], However, the toxicity of halogenated and deoxy sugars could possibly be exploited therapeutically for antiviral, antibacterial, or anticancer therapy. Examples are presented in detail later in this chapter. 

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