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Liver fatty Acid-Binding Protein: Structure and properties.

Tissue distribution and function of LFABP

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Liver fatty acid-binding protein (LFABP) belongs to the mammalian family of structurally related small cytosolic lipid binding proteins. LFABP is expressed in high concentrations in hepatocytes and co-expressed with intestinal fatty acid binding protein (IFABP), ileal lipid binding protein (ILBP), and cellular retinol binding protein II (CRBP II) in the small intestine, suggesting a functional specificity for different family members [1]. Fatty acid binding proteins (FABPs) are presumably involved in the uptake and targeting of long-chain fatty acids (LCFA) and in some cases other hydrophobic ligands, to intracellular organelles and metabolic pathways although their physiological functions are as yet unclear.

Specific properties of LFABP

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LFABP has particular characteristics within the FABP family which further support its unique functionality. This protein contains at least two fatty acid (FA) binding sites [2], while the other members have a single binding site for long-chain FA (LCFA) [3]; it binds a wide range of endogenous hydrophobic ligands besides LCFAs, among them acyl-CoAs [4] and lysophosphatidylcholine [5]. Besides these unique binding specificities, LFABP is distinguished from other family members by its diffusion-mediated mechanism of fatty acid transport under physiological ionic strength [6], which contrasts with the protein–membrane collisional process typical of IFABP as well as most of the other members of the FABP family of proteins [7].

LFABP structure

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FABPs share a common tertiary structure consisting of ten antiparallel β-strands that form a β-barrel, which is capped by two short α-helixes arranged as a helix-turn-helix segment. It has been proposed that this helical region is part of a “dynamic portal” that regulates fatty acid entry and exit from the internal cavity [8]. In solution one ligand is found to adopt a well-defined U shape which positions its long hydrophobic chain and ionized carboxylate deep within the cavity, whereas the other ligand has a more variable extended structure with its carboxylate group close to the surface.

Reference

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  1. ↑ [1] J. Storch, B. Corsico, The emerging functions and mechanisms of mammalian fatty acid-binding proteins, Annu. Rev. Nutr. 28 (2008) 73–95.
  2. ↑ J. Thompson, N. Winter, D. Terwey, J. Bratt, L. Banaszak, The crystal structure of the liver fatty acid-binding protein. A complex with two bound oleates, J. Biol. Chem. 14 (1997) 7140–7150.
  3. ↑ [3] J.C. Sacchettini, J.I. Gordon, L.J. Banaszak, Refined apoprotein structure of rat intestinal fatty acid binding protein produced in Escherichia coli, Biochim. Biophys. Acta 1747 (1989) 189–194.
  4. ↑ [4] G.V. Richieri, R.T. Ogata, A.M. Kleinfeld, Thermodynamic and kinetic properties of fatty acid interactions with rat liver fatty acid-binding protein, J. Biol. Chem. 271 (1996) 31068–31074.
  5. ↑ [5] R.E. Burrier, P. Brecher, Binding of lysophosphatidylcholine to the rat liver fatty acid binding protein, Biochim. Biophys. Acta 879 (1986) 229–239.
  6. ↑ [6] K.T. Hsu, J. Storch, Fatty acid transfer from liver and intestinal fatty acid-binding proteins to membranes occurs by different mechanisms, J. Biol. Chem. 271 (1996) 13317–13323.
  7. ↑ [7] A.E. Thumser, J. Storch, Liver and intestinal fatty acid-binding proteins obtain fatty acids from phospholipid membranes by different mechanisms, J. Lipid Res. 41 (2000) 647–656.
  8. ↑ [8] M.E. Hodsdon, D.P. Cistola, Ligand binding alters the backbone mobility of intestinal fatty acid-binding protein as monitored by 15 N NMR relaxation and 1H exchange, Biochemistry 36 (1997) 2278–2290.
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