NEW INSIGHTS INTO THE MOLECULAR-BASIS OF LECTIN-CARBOHYDRATE INTERACTIONS - A CALORIMETRIC AND STRUCTURAL STUDY OF THE ASSOCIATION OF HEVEIN TO OLIGOMERS OF N-ACETYLGLUCOSAMINE

Isothermal titration calorimetry was used to characterize thermodynami cally the association of hevein, a lectin hom the rubber tree latex, w ith the dimer and trimer of N-acetylglucosamine (GlcNAc), Considering the changes in polar and apolar accessible surface areas due to comple x formation, me found that the experimental binding heat capacities ca n be reproduced adequately by means of parameters used in protein-unfo lding studies, The same conclusion applies to the association of the l ectin concanavalin A with methyl-alpha-mannopyranoside. When reduced b y the polar area change, binding enthalpy values show a minimal disper sion around 100 degrees C. These findings resemble the convergence obs erved in protein-folding events; however, the average of reduced entha lpies for lectin-carbohydrate associations is largely higher than that for the folding of proteins, Analysis of hydrogen bonds present at le ctin-carbohydrate interfaces revealed geometries closer to ideal value s than those observed in protein structures, Thus, the formation of mo re energetic hydrogen bonds might well explain the high association en thalpies of lectin-carbohydrate systems, We also have calculated the e nergy associated with the desolvation of the contact zones in the bind ing molecules and from it the binding enthalpy in vacuum, This latter resulted 20% larger than the interaction energy derived from the use o f potential energy functions. (C) 1997 Wiley-Liss, Inc.