IQUIFIB   02644
INSTITUTO DE QUIMICA Y FISICOQUIMICA BIOLOGICAS "PROF. ALEJANDRO C. PALADINI"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Thermodynamics of SDS-induced unfolding of helical membrane proteins
Autor/es:
ALVARO RECOULAT; F. LUIS GONZÁLEZ FLECHA
Lugar:
Brisbane
Reunión:
Congreso; 18th International Biophysics Congress; 2014
Institución organizadora:
International Union of Pure and Applied Biophysics (IUPAB)
Resumen:
Understanding protein folding has been one of the great challenges in biochemistry and molecular biophysics. Although membrane proteins constitute about a third of the proteins encoded in known genomes, folding and stability studies on these proteins have been impaired mainly due to experimental limitations. Helical membrane proteins appear resistant to chemical denaturation by urea or guanidine hydrochloride but ionic detergents, such as SDS, have been efficiently used to unfold some of these. The amphipathic nature of detergents combine the possibility of disrupting tertiary contacts and solubilizing the secondary structure elements buried in biological membranes. As chaotropes, SDS binds to both native and denatured proteins, and unfolding is driven by the higher affinity for the denatured state. However, the binding mechanism is different. The driving force contains important favorable entropic contributions, making the denaturing effect evident at millimolar concentrations (SDS is about 1000-times more efficient denaturant than chaotropes). Besides, hydrophobic clusters of SDS molecules are able to induce helical structure in amphipathic non-structured chains. Thus, the final denatured state has high secondary structure content. Thermodynamic characterization of membrane protein stability requires experimental conditions where unfolding can be reversibly achieved. When this is possible, equilibrium thermodynamics provides the framework for determining the Gibbs free-energy change for transfer the membrane protein from an ideal one molar solution of the pure folded protein in water to an ideal one molar aqueous solution of the pure ?unfolded? protein, which is the accepted form to quantify the structural stability of a protein. Given the differences between the unfolded states induced by urea (or guanidine hydrochloride) and that formed when SDS is used as denaturant, comparison of the unfolding thermodynamic parameters cannot be directly performed although both quantities are extrapolated to zero denaturant concentration