A Study of Structurally Related Binding Properties of Concanavalin A Using Differential Scanning Calorimetry

Differential scanning calorimetry has been used to study the interactions between concanavalin A and different carbohydrates. It was found that the binding of carbohydrate to concanavalin A stabilizes the structure of the protein as judged by an increase in transition temperature of the lectin. Furthermore, the degree of stabilization is shown to be a function of the association constant for each sugar moiety. Interactions between concanavalin A and the glycoprotein horseradish peroxidase were also studied. On changing the molar ratio of peroxidase to concanavalin A from 0.1 to 16, an initial dramatic increase in the transition temperature for concanavalin A was observed, but at ratios above four the degree of stabilization decreased; no stabilization of peroxidase was found in molar ratios above one. Results are also presented on the importance of Mn2+ and Ca2+ for the stabilization of the concanavalin A structure and for its ability to bind carbohydrates. In the presence of Mn2+ ions alone, the lectin could not form the necessary conformation for binding the carbohydrate. However, with Ca2+ ions alone the lectin was able to bind the carbohydrate ligands, as judged by the shift in its transition temperature.