Recognition of beta-D-Gal p-(1-->3)-beta-D-Glc pNAc-OR acceptor analogues by the Lewis alpha-(1-->3/4)-fucosyltransferase from human milk.
The Lewis alpha-(1-->3/4)-fucosyltransferase (E.C. 2.4.1.65) transfers L-fucose from GDP-fucose to OH-4 of the Glc pNAc residue in the disaccharide beta-D-Galp-(1-->3)-beta-D-Glc pNAc-OR [R = (CH2)8COOMe] (1) to give the Lewis-A blood group determinant beta-D-Gal p-(1-->3)-[alpha-L-Fuc p-(1-->4)]-beta-D-Glc pNAc-OR. Five deoxy analogous of 1, as well as its N-propionyl derivative, were chemically synthesized and kinetically evaluated as both substrates and inhibitors for the enzyme from human milk. The unmodified acceptor 1 had Km = 640 microM with Vmax set arbitrarily to 100. The 6-deoxy (Km = 400 microM, V(max) = 90) and N-propionyl compounds (Km = 330 microM, V(max) = 170) remained excellent substrates while the 4-deoxy compound was a very weak competitive inhibitor with Ki = 9 mM. Deoxygenation of OH-2' and OH-4'(of the Gal residue) in 1 had little effect on the activity. The OH-6 group of the Gal residue proved to be critical for recognition by the enzyme since substitution of this group with hydrogen led to an inactive compound.
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Department of Chemistry, University of Alberta, Edmonton, Canada.
Hindsgaul
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D000818:Animals; D002240:Carbohydrate Sequence; D004187:Disaccharides / Q000138:chemical synthesis / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D005643:Fucose / Q000378:metabolism; D005647:Fucosyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005697:Galactosides / Q000138:chemical synthesis / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008895:Milk, Human / Q000201:enzymology*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D013379:Substrate Specificity
D004187:Disaccharides; D004791:Enzyme Inhibitors; D005697:Galactosides; D005643:Fucose; D005647:Fucosyltransferases; C019818:3-galactosyl-N-acetylglucosaminide 4-alpha-L-fucosyltransferase