Enzymatic Synthesis of N-Acetyllactosamine (LacNAc) Type 1 Oligomers and Characterization as Multivalent Galectin Ligands

Repeats of the disaccharide unit N-acetyllactosamine (LacNAc) occur as type 1 (Gal beta 1, 3GlcNAc) and type 2 (Gal beta 1, 4GlcNAc) glycosylation motifs on glycoproteins and glycolipids. The LacNAc motif acts as binding ligand for lectins and is involved in many biological recognition events. To the best of our knowledge, we present, for the first time, the synthesis of LacNAc type 1 oligomers using recombinant beta 1,3-galactosyltransferase from Escherichia coli and beta 1,3-N-acetylglucosaminyltranferase from Helicobacter pylori. Tetrasaccharide glycans presenting LacNAc type 1 repeats or LacNAc type 1 at the reducing or non-reducing end, respectively, were conjugated to bovine serum albumin as a protein scaffold by squarate linker chemistry. The resulting multivalent LacNAc type 1 presenting neo-glycoproteins were further studied for specific binding of the tumor-associated human galectin 3 (Gal-3) and its truncated counterpart Gal-3 Delta in an enzyme-linked lectin assay (ELLA). We observed a significantly increased affinity of Gal-3 Delta towards the multivalent neo-glycoprotein presenting LacNAc type 1 repeating units. This is the first evidence for differences in glycan selectivity of Gal-3 Delta and Gal-3 and may be further utilized for tracing Gal-3 Delta during tumor progression and therapy.