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Adipocyte Fatty Acid-Binding Protein: Interaction with Phospholipid Membranes and Thermal Stability Studied by FTIR Spectroscopy

1997; American Chemical Society; Volume: 36; Issue: 27 Linguagem: Inglês

10.1021/bi970679s

1943-295X

Arne Gericke, Elizabeth R. Smith, David J. Moore, Richard Mendelsohn, Judith Storch,

Lipid Membrane Structure and Behavior

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 β-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.