Interaction of Chicken Liver Basic Fatty Acid-Binding Protein (ChL-FABP) with Lipid Membranes

MARÍA VERÓNICA NOLAN, MASSIMILIANO PERDUCA, HUGO MÓNACO, BRUNO MAGGIO Y GUILLERMO MONTICH

Buenos Aires

Congreso; XlV International Biophysics Congress; 2002

IUPAB

We have studied the interactions of ChL-FABP with lipid model membranes. At low ionic strength, filtration binding assays indicate that this protein binds to palmitoyloleoylphosphatidylglycerol (POPG) large unilamellar vesicles (LUVs) but not to palmitoyloleoylphosphatidilcholine (POPC). FTIR spectroscopy revealed that binding to POPG at 25oC produces a decrease in the secondary structure of ChL-FABP. FTIR spectra as a function of temperature suggest a cooperative loss of secondary structure above 72oC for the protein in solution. The membrane-bound protein also shows an apparently cooperative transition at 56oC. Amide hydrogen-deuterium exchange for the pure protein and in presence of lipids was studied by FTIR. We have found that the rate of exchange for the protein in presence of POPC is less than the pure protein, mientras que for the protein incubated with POPG this rate is mucho mayor. The membrane-bound  protein at 25oC and low ionic strength can be released by increase in the ionic strength with recovery of the native FTIR spectra. Wide and low angle X-ray diffraction indicate that the binding of the protein produces an increase of the interlamellar spacing and an alteration of the laterall lipid-protein lattice. These results suggest that the conformational changes observed upon binding   do not correspond to an extensively unfolded protein but rather to a partially unfolded state, associated to the membrane, in reversible equilibrium with the protein in solution.