Recognition of β-D-Gal p-(1 → 3)-β-D-Glc pNAc-OR acceptor analogues by the Lewis α-(1 → 3/4)-fucosyltransferase from human milk

Article abstract of DOI:10.1016/0008-6215(96)00047-X

The Lewis α-(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 β-D-Gal p(1 → 3)-β-D-Glc pNAc-OR [R = (CH₂)₈COOMe] (1) to give the Lewis-A blood group determinant β-D-Gal p-(1 → 3)-[α-L-Fuc p-(1 → 4)]-β-D-Glc pNAc-OR. Five deoxy analogues 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 K_m = 640 μM with V_max set arbitrarily to 100. The 6-deoxy (K_m = 400 μM, V_max = 90) and N-propionyl compounds (K_m = 330 μM V_max = 170) remained excellent substrates while the 4-deoxy compound was a very weak competitive inhibitor with K_i = 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.