Poster Presentation 2014 International Biophysics Congress

The role of water during protein binding interactions and a suggested cause of entropy-enthalpy compensation observed during isothermal titration calorimetry studies (#689)

Robert J. Falconer 1 , Rachel L. Kilmister , Samuel Darby
  1. University of Sheffield, Sheffield, UK

Binding interactions between proteins and a range of partners’ plays an important role in a range of processes from cell physiology, drug function and nutrition. Isothermal titration calorimetry (ITC) was applied to study binding of purified proanthocyanidin oligomers to bovine serum albumin. The authors suggest tannin binding to proteins is opportunistic and involved multiple sites each with a different change in enthalpy (ΔH) and association constant (Ka) of binding. The titration curve had an apparent endothermic and exothermic component to binding which is consistent with water displacement and bond formation, respectively. The observation that there are competing endothermic and exothermic components to the binding reaction suggests that the observed change in enthalpy Hobs) is the sum of two opposing ΔH values and that care should be taken with interpretation of the calculated thermodynamic constants. Entropy-enthalpy compensation observed during ITC binding studies can be explained by an endothermic change in enthalpy associated with water reorganisation (ΔHs). The ΔHsskews both the ΔHobs and the calculated change in entropy (TΔScalc) equally.