2001 Volume 13 Issue 70 Pages 177-191
Poly-N-acetyllactosamine is a unique carbohydrate composed of N-acetyllactosamine (LacNAc) repeats and provides the backbone structure for additional modifications such as sialyl Lewisx, It is attached to N-glycans, O-glycans, and glycolipids and synthesized by the alternate addition of β1, 3-linked N-acetylglucosamine (GlcNAc) and β1, 4-linked galactose (Gal) by i-β1, 3-N-acetylglucosaminyltransferase (iGnT) and a member of the β1, 4-galactosyltransferase (β4Gal-T) gene family. Poly-N-acetyllactosamines in mucin-type O-glycans can be formed in core 2- and core 4-branched oligosaccharides, which are synthesized by core 2 β1, 6-N-acetylglucosaminyltransferase (C2GnT) and core 4 β1, 6-N-acetylglucosaminyltransferase (C4GnT), respectively.
β4Gal-TIV was found to be most efficient in the addition of a single Gal residue to core 2-branched oligosaccharides among the members of the β4Gal-T gene family and to synthesize poly-N-acetyllactosamine in core 2-branched O-glycans together with iGnT. On the other hand, β4Gal-TI was shown to be most efficient for poly-N-acetyllactosamine synthesis in N-glycans. In contrast to β4Gal-TI, the efficiency of β4Gal-TIV decreases dramatically as the acceptors contain more LacNAc repeats, consistent with the fact that core 2-branched O-glycans contain shorter poly-N-acetyllactosamines than N-glycans in many cells. Poly-N-acetyllactosamines in core 4-branched O-glycans were found to be synthesized most efficiently by iGnT and β4Gal-TI although the synthesis in core 4 branches is less efficient than in core 2 branches because of inefficient addition of GlcNAc to core 4 branches by iGnT. Thus, poly-N-acetyllactosamine extension in core 2- and core 4-branched O-glycans is differentially controlled by iGnT and different members of the β4Gal-T gene family.
