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Chemical modification of an alpha 3-fucosyltransferase; definition of amino acid residues essential for enzyme activity - PubMed

  • ️Wed Jan 01 1997

Chemical modification of an alpha 3-fucosyltransferase; definition of amino acid residues essential for enzyme activity

C J Britten et al. Biochim Biophys Acta. 1997.

Abstract

The biosynthesis of the carbohydrate antigen sialyl Lewis X (sLe(x)) is dependent on the activity of an alpha 3-fucosyltransferase (EC 2.4.1.152, GDP-fucose:Gal beta (1-4)GlcNAc-R alpha (1-3)fucosyltransferase). This enzyme catalyses the transfer of fucose from GDP-beta-fucose to the 3-OH of N-acetylglucosamine present in lactosamine acceptors. In this report, we have investigated the amino acids essential for the activity of a recombinant alpha 3-fucosyltransferase (FucT-VI) through chemical modification of the enzyme with group-selective reagents. FucT-VI activity was found to be particularly sensitive to the histidine-selective reagent diethylpyrocarbonate and the cysteine reagent N-ethylmaleimide, with IC50 values of less than 200 microM. Reagents selective for arginine and lysine had no effect on enzyme activity. The inclusion of GDP-beta-fucose during preincubation with NEM reduces the rate of inactivation whereas inclusion of an acceptor saccharide for the enzyme, Gal beta (1-4)GlcNAc, had no effect. No protective effect with either GDP-beta-fucose or Gal beta (1-4)GlcNAc was observed on treatment of the enzyme with diethylpyrocarbonate. These data suggest that in addition to an NEM-reactive cysteine in, or adjacent to, the substrate-binding site of the enzyme, FucT-VI possesses histidine residue(s) that are essential for enzyme activity.

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