Adipocyte fatty acid-binding protein: interaction with phospholipid membranes and thermal stability studied by FTIR spectroscopy.
Fatty acid-binding proteins (FABPs) found in many tissues constitute a family of low molecular weight proteins that are suggested to function as intracellular transporters of fatty acids. Studies of the transfer kinetics of fluorescent anthroyloxy-labeled long-chain fatty acids from FABP to model membranes led to the suggestion that the FABPs, typically considered to be cytosolic proteins, could nevertheless interact directly with membranes [Wootan, M. G., et al. (1993) Biochemistry 32, 8622-8627]. In the current study, the interaction of the adipocyte FABP (A-FABP) with vesicles of various phospholipids has been directly measured and confirmed with FTIR spectroscopy. The strength of this interaction was inferred from the lowering of the gel-liquid-crystal phase transition temperature as monitored from temperature-induced variations in the acyl chain CH2 stretching frequencies and from the intensities of the components of the CH2 wagging progressions. A-FABP interacts more strongly with anionic phospholipids (phosphatidylserine and cardiolipin) than with zwitterionic phosphatidylcholine. Unsaturation in the acyl chains leads to a greater reduction in Tm (stronger lipid-protein interaction). In contrast, neutralization of A-FABP surface charges by acetylation considerably weakens the interaction. Comparison of the shifts in lipid melting temperatures with those induced by other proteins suggests that A-FABP behaves like a typical peripheral membrane protein. The degree of membrane interaction correlates directly with the rate of fatty acid transfer, suggesting that contact between A-FABP and membranes is functionally related to its fatty acid transport properties. As expected, the protein exhibits a predominantly beta-sheet structure. It was found to aggregate with increasing temperature. With the exception of minor differences between the pure and lipid-associated A-FABP in the 1640-1660 cm-1 region, both the protein structure and thermal stability appeared essentially unchanged upon interaction with the lipid.
Gericke
A
A
Department of Chemistry, Rutgers University, Newark, New Jersey 07102, USA.
Smith
E R
ER
Moore
D J
DJ
Mendelsohn
R
R
Storch
J
J
D000107:Acetylation; D017667:Adipocytes / Q000737:chemistry*; D000818:Animals; D002308:Cardiolipins / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004355:Drug Stability; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D006358:Hot Temperature; D008081:Liposomes / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism*; D051379:Mice; D018996:Myelin P2 Protein / Q000737:chemistry / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D002308:Cardiolipins; D002352:Carrier Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D008081:Liposomes; D008563:Membrane Lipids; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids