Glycosyl, enzymatic transfer reactions

Enzymatic approaches to glycoside synthesis may circumvent these problems. Enzymes (i.e. nucleoside glycosyl transferases) are stereospecific and regioselective catalyzing glycosyl transfer reaction under mild conditions. Extensive protection-deprotection schemes are unnecessary and the control of anomeric configuration is managed. 

Ono, Y., Kitajima, M., Daikoku, S., Shiroya, T., Nishihara, S., Kanie, Y., Suzuki, K., Goto, S., and Kanie, O. (2008) Sequential enzymatic glycosyl-transfer reactions on a microfluidic device synthesis of a glycosaminogly-can linkage region tetrasaccharide. Lab Chip, 8, 2168-2173. 

Hen egg white lysozyme is a small protein of Mr 14 500 and 129 amino acid residues. This enzyme was introduced in Chapter 1, where it was pointed out that examination of the crystal structure of the enzyme stimulated most of the solution studies. Hen egg white lysozyme has the distinction of being the first enzyme to have had its structure solved by x-ray crystallography.207 It is an atypical member of the hexosaminidase class of glycosyl transfer enzymes. It catalyzes the hydrolysis of substrates with retention of stereochemistry. T4 lysozyme was for many years thought to have the same fold and mechanism of lysozyme, despite there being no sequence homology. But it has now been found that the T4 enzyme has inversion of configuration and so operates by a different mechanism.208,209 A mechanism proposed for the enzymatic reaction was based on the structure of the... 

Deoxyfluoro- and deoxy-sugars are useful in studies both of binding interactions between carbohydrates and proteins, and in mechanisms of glycosyl transfer. This paper describes how we have used such analogues to measure hydrogen bond strengths in a carbohydrate/ protein complex of known structure. It proceeds to review how such substitutions affect the rates of glycosyl transfer in a non-enzymatlc model reaction and then applies this Information to the results obtained in our enzymatic system. 

Sugar nucleotides 1-3 were found to act as donors for the a(l- 4)FucT. Their relative rates of reaction were estimated using a novel spectrophotometric coupled enzyme assay (22) which correlated the rate of production of GDP (equation I) with the rate of glycosyl transfer. The results, presented in Figure 3, show that 3-deoxy-L-fucose and D-arabinose were transferred at 1.7 and 6.0%, respectively, of the rate for L-fucose. The structures of the products were identified by an ELISA assay and scaled-up reactions ( 2 mg) allowed the product trisaccharides to be characterized by NMR (22)- 7 he natural Lewis-a trisaccharide determinant as well as two of its analogs could thus be prepared enzymatically. 

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