Chapter 9: Characterisation of Ligand Binding by Calorimetry

The number of proteins identified as targets for drug development is continuously increasing. While targets for drug development have been traditionally enzymes, the number of non-enzyme targets is fast approaching 50% of the total. Since non-enzyme targets are not amenable to rapid inhibition assays, the availability of methods that can measure and characterize the binding of ligands at a molecular level have become increasingly urgent. Isothermal titration calorimetry (ITC) is unique not only for its accuracy, but also for its unique ability to simultaneously measure binding affinity and its enthalpic and entropic components. Since the enthalpy and entropy changes reflect different types of interactions, ITC opens new dimensions to the analysis of binding. This chapter describes the characterization of different binding reactions including complex systems that involve proton coupling or cooperativity between ligands.