Measurement and characterization of binding interactions between proteins and low molecular weight (LMW) ligands are a focus of academic research and drug discovery. Isothermal titration calorimetry (ITC) directly measures heat released or absorbed in a binding event, providing means for studying protein-small molecule interactions in solution without the need for labeling or immobilization. Importantly, ITC is often utilized to characterize differences in entropic and enthalpic contributions to binding of novel ligands.

One of the challenges associated with the measurement and characterization of binding interactions is the broad affinity range that needs to be addressed. Binding affinity values (measured as the dissociation equilibrium constant, KD) of small compounds binding to a target protein in a typical drug discovery project can span from low millimolar to subnanomolar range. Dependent on the biochemical system under study (receptor, transporter, enzyme, etc.), an equally broad affinity range is relevant for academic research.

Highly sensitive ITC instruments and properly designed experiments greatly simplify characterization of binding interactions. Our new ITC system, MicroCal PEAQ-ITC, is designed to improve signal stability, mixing, and signal-to-noise characteristics. These changes, along with an advanced experimental design feature integrated in the easy-to-use data analysis software, facilitate optimization of experiments for the studies of challenging interactions. This white paper highlights the beneficial features of the new MicroCal PEAQ-ITC instrument and software for the analysis of binding interactions through direct and competitive titrations.