Synthesis of Poly-N-acetyllactosamine in Core 2 Branched O-Glycans

• Published in: The Journal of biological chemistry Vol. 273; no. 52; pp. 34843 - 34849
• Main Authors: Ujita, Minoru, McAuliffe, Joseph, Schwientek, Tilo, Almeida, Raquel, Hindsgaul, Ole, Clausen, Henrik, Fukuda, Minoru
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 25-12-1998
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.52.34843

Poly- N -acetyllactosamine is a unique carbohydrate composed of N -acetyllactosamine repeats and provides the backbone structure for additional modifications such as sialyl Le x . Poly- N -acetyllactosamines in mucin-type O -glycans can be formed in core 2 branched oligosaccharides, which are synthesized by core 2 β-1,6- N -acetylglucosaminyltransferase.
Using a β-1,4-galactosyltransferase (β4Gal-TI) present in milk and the recently cloned β-1,3- N -acetylglucosaminyltransferase, the formation of poly- N -acetyllactosamine was found to be extremely inefficient starting from a core 2 branched oligosaccharide, GlcNAcβ1→6(Galβ1→3)GalNAcα→R.
Since the majority of synthesized oligosaccharides contained N -acetylglucosamine at the nonreducing ends, galactosylation was judged to be inefficient, prompting us to test novel members
of the β4Gal-T gene family for this synthesis. Using various synthetic acceptors and recombinant β4Gal-Ts, β4Gal-TIV was found
to be most efficient in the addition of a single galactose residue to GlcNAcβ1→6(Galβ1→3)GalNAcα→R. Moreover, β4Gal-TIV, together
with β-1,3- N -acetylglucosaminyltransferase, was capable of synthesizing poly- N -acetyllactosamine in core 2 branched oligosaccharides. On the other hand, β4Gal-TI was found to be most efficient for poly- N -acetyllactosamine synthesis in N -glycans. In contrast to β4Gal-TI, the efficiency of β4Gal-TIV decreased dramatically as the acceptors contained more N -acetyllactosamine repeats, consistent with the fact that core 2 branched O -glycans contain fewer and shorter poly- N -acetyllactosamines than N -glycans in many cells. These results, as a whole, indicate that β4Gal-TIV is responsible for poly- N -acetyllactosamine synthesis in core 2 branched O -glycans.