Enzymatic synthesis of natural and 13C enriched linear poly-N-acetyllactosamines as ligands for galectin-1

Abstract

As part of a study of protein-carbohydrate interactions, linear N-acetyl-polyllactosamines [Galβ1,4GlcNAcβ1,3](n) were synthesized at the 10-100 μmol scale using enzymatic methods. The methods described also provided specifically [1-13C]galactose-labeled tetra- and hexasaccharides ([1-13C]-Galβ1,4GlcNAcβ1,3Galβ1,4Glc and Galβ1,4GlcNAcβ1,3[1-13C]Galβ1,4GlcNAcβ1,3Galβ1,4Glc) suitable for NMR studies. Two series of oligosaccharides were produced, with either glucose or N-acetlyglucosamine at the reducing end. In both cases, large amounts of starting primer were available from human milk oligosaccharides (trisaccharide primer GlcNAcβ1,3Galβ1,4Glc) or via transglycosylation from N-acetyllactosamine. Partially purified and immobilized glycosyltransferases, such as bovine milk β1,4 galactosyltransferase and human serum β1,3 N- acetylglucosaminyltransferase, were used for the synthesis. All the oligosaccharide products were characterized by 1H and 13C NMR spectroscopy and MALDI-TOF mass spectrometry. The target molecules were then used to study their interactions with recombinant galectin-1, and initial 1H NMR spectrescopic results are presented to illustrate this approach. These results indicate that, for oligomers containing up to eight sugars, the principal interaction of the binding site of galectin-1 is with the terminal N-acetyllactosamine residues.