Using isothermal titration calorimetry for the determination of thermodynamic properties of protein-ligand and protein-protein interactions

Abstract

Protein-protein and protein-ligand interactions are crucial events for the regulation of proteins and protein activity, for instance, it is responsible for enzyme activation or inhibition, by conformational changes in proteins for cell signaling, transport and storage of substances, etc. Few experimental techniques allow studying these types of interactions in solution, and provide a wide range of thermodynamic data such as isothermal titration calorimetry (ITC). This method uses heat, a universal probe, to yield information such as stoichiometry of the interaction, the interaction enthalpy, affinity constant (and change in free energy) and interaction entropy. Besides this information, ITC experiments at different temperatures allow to determine the change of heat capacity of interaction. Altogether, these data provide a "thermodynamic signature" of interaction that can assist in understanding the mechanism of interaction involved in the molecular level, especially with the aid of structural information obtained by other techniques. The molecular understanding of protein-ligand or protein-protein interactions may assist in understanding the mechanism of protein regulation and may also contribute to the rational drug design. The ITC also allows to monitor the flow of an enzymatic reaction producing information as a constant Michaelis-Menten, constant of catalysis and inhibition constant when performed in the presence of inhibitors. Thus, the objective of this project is to apply the ITC to obtain thermodynamic data for protein-ligand or protein-protein interactions to correlate this information with structural data, at low and high resolution, of several proteins in the study group BMB/IQSC/USP. The group BMB cover research in four main lines involving molecular chaperones Hsp90 and Hsp70 families (and their co-chaperones) from human and protozoa, also a trypanocidal-metabolizing enzyme. The ITC technique can considerably help the characterization of these proteins under study in the group BMB. (AU)