Thermodynamic model for the analysis of calorimetric data of oligomeric proteins

INES BURGOS; SERGIO DASSIE; GERARDO FIDELIO

JOURNAL OF PHYSICAL CHEMISTRY B

American Chemical Society

Lugar: Washington; Año: 2008 vol. 112 p. 14325 - 14333

1089-5647

The thermodynamic parameters for the process of protein unfolding can be obtained through differential scanning calorimetry. However, the unfolding process may not be a two state one. Between the native and the unfolded state there may be association or dissociation processes or the formation of an intermediate state. As a consequence of this, the precise interpretation of the calorimetric data should be done with a specific thermodynamic model. In this work we present two general models for the unfolding process of an oligomeric protein: (model A) and (model B). In model A, the first step represents the dissociation of the oligomer into the monomeric native species and the second step represents the denaturation process. In model B the first step represents the conformational change of the oligomer and the second step the dissociation of this species with the concomitant unfolding process. A canonical ensemble was employed to describe these systems, considering that the total protein concentration remains constant. In the present work we show and analyze the behavior of these systems in different conditions, and how could this analysis help with the identification of the unfolding mechanism experimentally observed.