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