Characterization of Vesicle-Micelle transitions by Fluorescence Correlation Spectroscopy (FCS) and Isothermal Titration Calorimetry (ITC)

MARTÍN DODES TRAIAN; MARÍA FLORENCIA PIGNATARO; VALERIA LEVI; FRANCISCO LUIS GONZÁLEZ FLECHA

Villa Carlos Paz

Congreso; XLII Reunión Anual de la Sociedad Argentina de Biofísica; 2013

Sociedad Argentina de Biofísica

Structural and kinetic studies of membrane proteins require their reconstitution in amphiphilic systems to ensure their proper folding and stability in aqueous media. The structure of these systems ranges from micelles to vesicles depending on the relative concentrations of phospholipids and detergent. To characterize the behaviour of these systems and the transitions among them we used Fluorescence Correlation Spectroscopy (FCS) and Isothermal Titration Calorimetry (ITC). We used FCS to measure the diffusion coefficient of the particles and thus this technique allowed us to gather information about the heterogeneity of the studied systems. ITC allows detecting membrane solubilisation by measuring the heat exchanged upon the addition of detergents. Working with a system similar to that used in membrane activity protocols we could observe the abrupt change in size characteristic of a micelle-vesicle transition at a phospholipid / detergent mole fraction around 0.75 and by ITC around 0.8 mole fraction the heat signature changes from endothermic to exothermic. These experiments contribute to our understanding of the correlation between the physical properties of the amphipilic systems and the function of membrane proteins inserted in them.