The acceptor and site specificity of alpha 3-fucosyltransferase V - High reactivity of the proximal and low of the distal, Gal beta 1-4GlcNAc unit ini-type polylactosamines

We report here on in vitro acceptor and site specificity of recombinant alp ha3-fucosyltransferase V (Fuc-TV) with 40 oligosaccharide accepters. Gal be ta1-4GlcNAc (LN) and GalNAc beta1-4GlcNAc (LDN) reacted rapidly; Gal beta1- 3Glc-NAc (LNB) reacted moderately, and GlcNAc beta1-4GlcNAc (N,N'-diacetyl- chitobiose) reacted slowly yet distinctly. In neutral and terminally alpha3 -sialylated polylactosamines of i-type, the reducing end LN unit reacted ra pidly and the distal (sialyl)LN group very slowly; the midchain LNs reveale d intermediate reactivities. The data suggest that a distal LN neighbor enh ances but a proximal LN neighbor reduces the reactivity of the midchain LNs . This implies that Fuc-TV may bind preferably the tetrasaccharide sequence Gal beta1-4GlcNAc beta1-3Gal beta1-4GlcNAc for transfer at the underlined monosaccharide. Terminal alpha3-sialylation of i-type polylactosamines almo st doubled the reactivities of the LN units at all positions of the chains. We conclude that, in comparison with human Fuc-TIV and Fuc-TIX, Fuc-TV rea cted with a highly distinct site specificity with i-type polylactosamines. The Fuc-TV reactivity of free LNB resembled that of LNB beta1-3'R of a poly lactosamine, contrasting strongly with the dissimilarity of the reactivitie s of the analogous pair of LN and LN beta1-3'R. This observation supports t he notion that LN and LNB may be functionally bound at distinct sites on Fu c-TV surface. Our data show that Fuc-TV worked well with a very wide range of LN-glycans, showing weak reactivity only with distal (sialyl)LN units of i-type polylactosamines, biantennary N-glycans, and I branches of polylact osamines.