Thermodynamic and structural analysis of homodimeric proteins: Model of β-lactoglobulin

BURGOS INÉS; DASSIE SERGIO; VILLARREAL MARCOS ARIEL; FIDELIO GERARDO DANIEL

BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS

ELSEVIER SCIENCE BV

Año: 2011 p. 383 - 391

1570-9639

The energetics of protein homo-oligomerization was analyzed in detail with the application of a general thermodynamicmodel. We have studied the thermodynamic aspects of protein–protein interaction employingβ-lactoglobulin A from bovine milk at pH=6.7 where the protein is mainly in its dimeric form. We performeddifferential calorimetric scans at different total protein concentration and the resulting thermogramswere analyzed with the thermodynamic model for oligomeric proteins previously developed. The thermodynamicmodel employed, allowed the prediction of the sign of the enthalpy of dimerization, the analysis ofcomplex calorimetric profiles without transitions baselines subtraction and the obtainment of the thermodynamicparameters from the unfolding and the association processes and the compared with association parametersobtained with Isothermal Titration Calorimetry performed at different temperatures. Thedissociation and unfolding reactions were also monitored by Fourier-transform infrared spectroscopy andthe results indicated that the dimer of β-lactoglobulin (N2) reversibly dissociates into monomeric units (N)which are structurally distinguishable by changes in their infrared absorbance spectra upon heating.Hence, it is proposed that β-lactoglobulin follows the conformational path induced by temperature:N2⇌2N⇌2D. The general model was validated with these results indicating that it can be employed in thestudy of the thermodynamics of other homo-oligomeric protein systems.