Protein unfolding coupled to ligand binding. Differential scanning calorimetry simulation approach.

CELEJ, M.S.; DASSIE, S.A; FIDELIO. G.D.

JOURNAL OF CHEMICAL EDUCATION

AMER CHEMICAL SOC

Año: 2005 vol. 82 p. 85 - 92

0021-9584

The aim of this work is to present to undergraduate and postgraduate chemistry students in the field of biochemistry and biophysics the physicochemical basis underlying the changes in protein thermostability upon ligand binding. The paper deals with the thermodynamic coupling of thermal unfolding with ligand binding. The effect of ligand binding on the protein thermal behavior can be easily followed by using differential scanning calorimetry (DSC). We present a simple model allowing to obtain the thermogram (heat capacity-temperature course) by taking into account the relatives changes in the proportion of protein states during thermal unfolding. The model envisages the binding of a ligand to a single site either to native, unfolded or to both protein conformations. Besides a mathematical description of the equilibriums involved in the system, the model provides the general formulation allowing to simulate thermograms, together with the changes of protein species during the temperature scan. First, we describe the ligand interaction emphasizing the relationship between protein stability parameters and changes of species in equilibrium. Second, we describe the logical manifestation of thermograms with bimodality as well as the effect of changes in the concentration of the interacting species but keeping constant the protein to ligand mole ratio.