title: Binding of cationic lipids to milk β-lactoglobulin.
abstract: We determined the bindings of several lipids such as cholesterol (CHOL), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), dioctadecyldimethyl-ammoniumbromide (DDAB), and dioleoylphosphatidylethanolamine (DOPE) to β-lactoglobulin (β-LG) at physiological conditions. FTIR, CD, and fluorescence spectroscopic methods as well as molecular modeling were used to determine the binding of lipid-protein complexes. Structural analysis showed that lipids bind β-LG via both hydrophilic and hydrophobic interactions with overall binding constants of K(CHOL-β-LG) = 6.0 (±0.6) × 10(3) M(-1), K(DOPE-β-LG) = 6.5 (±0.7) × 10(3) M(-1), K(DDAB-β-LG) = 1.6 (±0.3) × 10(4) M(-1), and K(DOTAP-β-LG) = 2.2 (±0.67) × 10(4) M(-1). The number of lipid bound per protein molecule (n) was 0.8 (CHOL), 0.7 (DOPE), 1.0 (DDAB), and 1.3 (DOTAP). Molecular modeling showed the participation of several amino acid residues in lipid-protein complexation with the order of binding DOTAP > DDAB > DOPE > CHOL. Alterations of the protein conformation were observed in the presence of lipids with a minor decrease in β-sheet and an increase in turn structure.
authors.affiliation: Département de Chimie-Biologie, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada.
authors.forename: Imed
authors.initials: I
authors.lastname: Hasni
authors.forename: Philippe
authors.initials: P
authors.lastname: Bourassa
authors.forename: Heidar-Ali
authors.initials: HA
authors.lastname: Tajmir-Riahi
mesh_terms: D000818:Animals; D002412:Cations / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D002942:Circular Dichroism; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002412:Cations; D005229:Fatty Acids, Monounsaturated; D007782:Lactoglobulins; D010714:Phosphatidylethanolamines; D000644:Quaternary Ammonium Compounds; C046112:didodecyldimethylammonium; C094877:dioleoyl phosphatidylethanolamine; D002784:Cholesterol; C070046:1,2-dioleoyloxy-3-(trimethylammonium)propane