Thermodynamic Analysis of Protein-Lipid Interactions by Isothermal Titration Calorimetry

Isothermal titration calorimetry is a highly sensitive and powerful technique for the study of molecular interactions. This method can be applied universally for studying the interaction between moleculeAbstracts, molecular assembles and ions as it measures the heat changes resulting from such interactions and does not need any probe molecule/moiety to be incorporated into the system under investigation. This method has been applied quite extensively to investigate the interaction of proteins with other biomolecules such as small ligands, other proteins, nucleic acids, lipid membranes as well as to study the interaction of antibodies, drugs, metal ions and nanoparticles with target proteins or antigens, nucleic acids, and membranes. In this chapter, we describe the application of ITC for the investigation of thermodynamics of protein-lipid interaction. A number of important parameters such as enthalpy of binding (ΔH), entropy of binding (ΔS), association constant (K_a), binding stoichiometry (n) and free energy of binding (ΔG) can be obtained from a single calorimetric titration, providing a complete thermodynamic characterization of the interaction. The method is described in detail taking the major protein of the bovine seminal plasma, PDC-109, which exhibits a high preference for interaction with choline-containing lipids, as an example. The method can be applied to investigate thermodynamic parameters associated with the interaction of other soluble proteins with lipid membranes.