Fuc-TIX: a versatile  1,3-fucosyltransferase with a distinct acceptor- and site-specificity profile

[alpha]1,3-Fucosyltransferases (Fuc-Ts) convert N-acetyllactosamine (LN, Gal[beta]1-4GlcNAc) to Gal[beta]1-4(Fuc[alpha]1-3)GlcNAc, the Lewis x (CD15, SSEA-1) epitope, which is involved in various recognition phenomena. We describe details of the acceptor specificity of [alpha]1,3-fucosyltransferase IX (Fuc-TIX). The unconjugated N- and O-glycan analogs LN[beta]1-2Man, LN[beta]1-6Man[alpha]1-OMe, LN[beta]1-2Man[alpha]1-3(LN[beta]1-2Man[alpha]1-6)Man[beta]1-4GlcNAc, and Gal[beta]1-3(LN[beta]1-6)GalNAc reacted well in vitro with Fuc-TIX present in lysates of appropriately transfected Namalwa cells. Fuc-TIX reacted well with the reducing end LN of GlcNAc[beta]1-3'LN (underscored site reacted) and GlcNAc[beta]1-3'LN[beta]1-3'LN (both LNs reacted), but very poorly with the reducing end LN of LN[beta]1-3'LN. However, Fuc-TIX reacted significantly better with the non-reducing end LN as compared to the other LN units in the glycans LN[beta]1-3'LN and LN[beta]1-3'LN[beta]1-3'LN[beta]1-3'LN, confirming our previous data on LN[beta]1-3'LN[beta]1-OR. In contrast, the sialylated glycan Neu5Ac[alpha]2-3'LN[beta]1-3'LN[beta]1-3'LN[beta]1-3'LN was fucosylated preferentially at the two most reducing end LN units. We conclude that Fuc-TIX is a versatile [alpha]1,3-Fuc-T, that (1) generates distal Lewis x epitopes from many different acceptors, (2) possesses inherent ability for the biosynthesis of internal Lewis x epitopes on growing polylactosamine backbones, and (3) fucosylates the remote internal LN units of [alpha]2,3-sialylated i-type polylactosamines.