Thermodynamic binding studies of cell surface carbohydrate epitopes to galectins-1, -3, and -7: Evidence for differential binding specificities

Abstract

Binding of a series of sialylated and non-sialylated cell surface carbohydrates to bovine heart galectin-1, recombinant murine galectin-3, and recombinant human galectin-7 was investigated by isothermal titration microcalori metry (ITC) and hemagglutination inhibition measurements. Galectin-7 shows nearly equal affinities for lactose and Galbeta(1–4)GlcNAc (LacNAc-II). Galectin-7, however, displays six- and 11-fold weaker affinity for LacNAc-II compared with galectins-1 and -3, respectively. The affinity of galectin-7 for LacNAc-II containing oligosaccharides is also weaker than the other two galectins. ITC measurements show that all three galectins bind to di- and trimeric oligomers of LacNAc-II, which are epitopes found in poly-N-acetyllactosamine chains of glycoprotein receptors, with affinity constants similar to that of LacNAc-II. The binding valencies of the di- and trimeric LacNAc-II oligomers were observed to be one from ITC measurements, indicating formation of 1:1 complexes with all three galectins. Thus, galectins-1, -3, and -7 all possess binding sites that primarily accommodate one LacNAc-II moiety per monomer of protein. Sialylated oligosaccharides show different specificities for the three galectins. While 2,3-sialyl LacNAc-II binds to all three galectins, 2,6-sialyl LacNAc-II fails to bind to any of the galectins; 2,6-sialylated diLacNAc binds well to galectin-3 and galectin-7, but only weakly to galectin-1. Similar results are obtained with 2,6-sialyl lacto-N-neo-tetraose, which has a reducing end lactose moiety. Thus, unlike galectin-1, which predominantly recognizes non-reducing terminal LacNAc-II residues in oligosaccharides, galectins-3 and -7 recognize both non-reducing terminal LacNAc-II residues as well as internal LacNAc-II and lactose residues in sialylated and non-sialylated oligosaccharides.Key words: isothermal titration microcalorimetry, galectins, binding specificities, lectins, carbohydrates.

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

“…Our analysis flanked by positive controls revealed an indistinguishable behavior of galectin-7 relative to homodimeric galectin-1. This result can completely be reconciled with the similar potency of both galectins in haemagglutination of trypsinized and glutaraldehyde-fixed rabbit erythrocytes, a hallmark of di-and oligovalent carbohydrate-binding proteins Ahmad et al, 2002). Multivalency effects noted in inhibition assays with branched Nglycans are in line with the detected consequences of aggregation processes in the presence of an excess of glycodendrimers in nano-ESI mass spectrometry.…”

“…In contrast to galectin-1 homing in on nonreducing terminal Lac/LacNAc units, galectin-7 (and also galectin-3) recognize both terminal and internal ligand sites (Ahmad et al, 2002). In the case of the GM 1 pentasaccharide, the tested galectins bound to the matrix-immobilized ligand in a very similar manner.…”

Phosphorylation of adhesion- and growth-regulatory human galectin-3 leads to the induction of axonal branching by local membrane L1 and ERM redistribution

“…Neuropilin-1, a receptor for the guidance cue semaphorin3A, regulates dendritic branching (Morita et al, 2006), and a glycoform has been identified recently as a galectin-1 ligand (Hsieh et al, 2008). Considering that Gal-1 and Gal-3 display common affinities for -galactosides including ganglioside GM1 and the N-glycans of asialofetuin (Ahmad et al, 2002;André et al, 2005;Dam et al, 2005;Hirabayashi et al, 2002), neuropilin-1 appears to be a suitable candidate to mediate the induction of branching by bound pGal-3. However, no evidence for an interaction between pGal-3 and neuropilin was observed (Fig.…”

Human galectins as sensors for apoptosis/necrosis‐associated surface changes of granulocytes and lymphocytes

“…Galectin-3, which tolerates a2,6-sialylation in poly(N-acetyllactosamine) chains (44), strongly bound to such cells. But it failed to be discriminatory on the level of cell staining, regardless of the presence or absence of the collagenase-sensitive stalk, which is involved in pentamerization (45).…”