Liver fatty acid binding protein enhances sterol transfer by membrane interaction.
Among the large family of fatty acid binding proteins, the liver L-FABP is unique in that it not only binds fatty acids but also interacts with sterols to enhance sterol transfer between membranes. Nevertheless, the mechanism whereby L-FABP potentiates intermembrane sterol transfer is unknown. Both fluorescence and dialysis data indicate L-FABP mediated sterol transfer between L-cell fibroblast plasma membranes occurs by a direct membrane effect: First, dansylated-L-FABP (DNS-L-FABP) is bound to L-cell fibroblast plasma membranes as indicated by increased DNS-L-FABP steady state polarization and phase resolved limiting anisotropy. Second, coumarin-L-FABP (CPM-L-FABP) fluorescence lifetimes were significantly increased upon interaction with plasma membranes. Third, dialysis studies with 3H-cholesterol loaded plasma membranes showed that L-FABP added to the donor compartment of the dialysis cell stimulated 3H-cholesterol transfer whether or not the dialysis membrane was permeable to L-FABP. However, L-FABP mediated intermembrane sterol transfer did require a sterol binding site on L-FABP. Chemically blocking the ligand binding site also inhibited L-FABP activity in intermembrane sterol transfer. Finally, L-FABP did not act either as an aqueous carrier or in membrane fusion. The fact that L-FABP interacted with plasma membrane vesicles and required a sterol binding site was consistent with a mode of action whereby L-FABP binds to the membrane prior to releasing sterol from the bilayer.
Woodford
J K
JK
Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati Medical Center, OH 45267-0524, USA.
Behnke
W D
WD
Schroeder
F
F
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005456:Fluorescent Dyes; D007739:L Cells; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018996:Myelin P2 Protein / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding; D051381:Rats; D013261:Sterols / Q000378:metabolism*
D002352:Carrier Proteins; C493320:Fabp1 protein, mouse; C493321:Fabp1 protein, rat; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D013261:Sterols