THERMODYNAMICS OF CARBOHYDRATE-BINDING TO GALECTIN-1 FROM CHINESE-HAMSTER OVARY CELLS AND 2 MUTANTS - A COMPARISON WITH 4 GALACTOSE-SPECIFIC PLANT-LECTINS

The thermodynamics of carbohydrate binding to the 14 kDa dimeric beta- galactoside-binding lectin galectin-1 (Gal-1) from Chinese hamster ova ry cells and four galactose-specific plant lectins were investigated b y isothermal titration microcalorimetry. Recombinant Gal-1 from Escher ichia coli, a Cys-->Ser mutant with enhanced stability (C2S-Gal-1), an d a monomeric mutant of the lectin (N-Gal-1) were studied along with t he soybean agglutinin and the lectins from Erythrina indica, Erythrina crystagalli, and Erythrina corollodendrum. Although the pattern of as sociation constants of the Erythrina lectins was similar for mono- and disaccharides. variations exist in their enthalpy of binding (-Delta H) values for individual carbohydrates. While the Erythrina lectins sh ow greater affinities and -Delta H values for lactose and N-acetyllact osamine, the soybean agglutinin possesses similar affinities for methy l beta-galactopyranoside, lactose, and N-acetyllactosamine and a great er -Delta H value for the monosaccharide. Gal-1 and the plant lectins possess essentially the same affinities for N-acetyllactosamine; howev er, the animal lectin shows a lower -Delta H value and more favorable binding entropy for the disaccharide. While Gal-1, C2S-Gal-1, and N-Ga l-1 all possess essentially the same affinities for N-acetyllactosamin e, the two mutants possess much lower -Delta H values, even though the mutation site(s) are far removed from the carbohydrate binding site. These results indicate that there are different energetic mechanisms o f carbohydrate binding between galectin-1, its two mutants, and the Ga 1-specific plant lectins.