Applications of Isothermal Titration Calorimetry to Lectin-Carbohydrate Interactions

The biological activities of lectins appear to be primarily due to their carbohydrate-binding properties. Thus, determination of the mechanisms of binding and specificities of lectins for carbohydrates and glycoconjugates provides insight into their biological properties. Historically, the relative affinities and specificities of lectins for carbohydrates were first addressed using hemagglutination inhibition, equilibrium dialysis, and quantitative precipitation inhibition techniques. Additionally techniques including gradient affinity chromatography, nuclear magnetic resonance, and surface plasmon resonance have been used. However, all of these methods either suffer from being indirect measurements of binding constants or have special conditions required for the measurements. The major advantage of isothermal titration calorimetry (ITC) in determining quantitative binding constants for carbohydrate-lectin interactions is that it provides direct determination of the association constant (K_a) for binding of unmodified molecules in solution by measuring their heat of binding. ITC also provides the stoichiometry of binding and all thermodynamic binding parameters. This chapter provides selective examples of the application of ITC to lectin-carbohydrate interactions including multivalent interactions.