Conformation of L-BAPB at lipid membrane interface. Effect of membrane surface electrostatic potential

MARÍA B. DECCA, VANESA V. GALASSI, GUILLERMO G. MONTICH

Los Cocos, Cordoba, Argentina

Congreso; Sociedad Argentina de Biofísica; 2009

Sociedad Argentina de Biofísica

L-BABP is a basic protein, member of a large family of proteins known as FABPs. They are involved in the transport and released of non-polar compounds to lipid membranes. L-BABP association to anionic lipid membranes is driven by electrostatic interactions. We have previously shown that association to lipid membranes promotes conformational changes in L-BABP, which are sensitive to the phase state of lipid membranes.                 The aim of this work was to evaluate the effect of the membrane surface electrostatic potential on the conformation of L-BABP. We studied the interaction of L-BABP with LUVs of different lipids in the presence of 0.1 M NaCl. Protein conformation was evaluated by FT-IR spectroscopy. Electrokinetic potentials of LUVs were measured by the autocorrelation of dynamic light scattering. We found that L-BABP associated to saturated anionic lipids membranes in gel phase retains the FT-IR spectrum of the free protein in solution, whereas L-BABP associated to saturated membranes (e.g. DMPG) in liquid-crystalline phase acquires a less structured conformation, characteristic of a partly unfolded state. No changes in L-BABP secondary structure were observed after binding to unsaturated POPG lipid membranes, even thought this membrane is in liquid-crystalline phase at the temperatures studied. Measurements of membrane electrokinetic potential correlates with protein conformation at the interface: POPG membranes have the lowest values æ-potential measured, whereas DMPG membranes have lower æ-potential in gel phase than in liquid crystalline phase. To further evaluate the influence of surface electrostatic potential in the conformation of membrane bound L-BABP, we modified the average surface charge density of DMPG membranes by adding small amounts of the zwitterionic lipid DMPC. FT-IR spectrum of LPABP is sensitive to the proportion of PC in the mixture. As low as 10 mol% PC prevents any changes in L-BABP secondary structure after protein association with lipid membranes.