Isothermal Titration Calorimetry and Molecular Dynamics Simulation Studies on the Binding of Indometacin with Human Serum Albumin

Human serum albumin (HSA) is the most abundant protein in the blood plasma. Drug binding to HSA is crucial to study the absorption, distribution, metabolism, efficiency and bioavailability of drug molecules. In this study, isothermal titration calorimetry and molecular dynamics simulation of HSA and its complex with indometacin (IM) were performed to investigate thermodynamics parameters and the structural changes induced by the ligand binding, respectively. To estimate the binding affinity of drug molecule to subdomains IB and IIA in HSA protein, binding free energies were calculated using the Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA). The binding association constant (Ka) and the standard Gibbs free energy changes (G) of indometacin binding to the protein obtained from ITC technique are 9.12 103 M-1 and -5422 Kcal mol-1, respectively. All results indicate that the binding affinity of the drug molecule to subdomain IIA is more than that of subdomain IB of HSA. Thus the obtained thermodynamics characteristics, hydrophobic forces most likely played a major role, but hydrogen bonding also could not be ignored. One of the most important finding is that the subdomain IIA of HSA is the main binding site for indomethacin that confirmed by molecular dynamics simulation.