Structural and functional interaction of fatty acids with human liver fatty acid‐binding protein (L‐FABP) T94A variant

Abstract

The human liver fatty acid binding protein (L-FABP) T94A variant, the most common in the FABP family, has been associated with elevated liver triglyceride (TG) levels. How this amino acid substitution elicits these effects is not known. This issue was addressed with human recombinant wild-type (WT, T94T) and T94A variant L-FABP proteins as well as cultured primary human hepatocytes expressing the respective proteins (genotyped as TT, TC, and CC). T94A substitution did not or only slightly alter L-FABP binding affinities for saturated, monounsaturated, or polyunsaturated long chain fatty acids (LCFA), nor did it change the affinity for intermediates in TG synthesis. Nevertheless, T94A substitution markedly altered the secondary structural response of L-FABP induced by binding LCFA or intermediates of TG synthesis. Finally, T94A substitution markedly diminished polyunsaturated fatty acid, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), induction of peroxisome proliferator-activated receptor alpha (PPARα) - regulated proteins such as L-FABP, fatty acid transport protein 5 (FATP5), and PPARα itself in cultured primary human hepatocytes. Thus, while T94A substitution did not alter the affinity of human L-FABP for LCFAs, it significantly altered human L-FABP structure and stability as well as conformational and functional response to these ligands.

Recent insights into the biological functions of liver fatty acid binding protein 1

“…A signifi cant trend of higher plasma triglyceride ( 98,99 ) and LDL-cholesterol concentrations was also observed ( 100 ). This genetic variation alters the protein structure, stability, and interaction with fatty acids as well as PPAR ␣ agonists, and subsequently impacts fatty acid metabolism and PPAR ␣ activation ( 99,101,102 ). Therefore, FABP1 T94A missense mutation could infl uence obesity indices and the risk to exhibit residual hypertriglyceridemia following lipidlowering therapy.…”

Δ9-Tetrahydrocannabinol induces endocannabinoid accumulation in mouse hepatocytes: antagonism by Fabp1 gene ablation

“…in (21). While the human FABP1 T94A variant protein differs only modestly from its wild-type FABP counterpart in affinities for endocannabinoids (AEA, 2-AG) (25) as well as a variety of other ligands (26)(27)(28)(29), the conformation of FABP1 T94A variant is much less responsive to ligand-induced change (25,26) which in turn diminishes its ability to enter nuclei, interaction with, and activation of peroxisome proliferator activated receptor- (PPAR) therein (29).…”

Loss of L-FABP, SCP-2/SCP-x, or both induces hepatic lipid accumulation in female mice

“…Human genetic variants in the SCP-2/SCP-x gene are associated with lipid metabolic abnormalities [92]; ii) L-FABP [93]. Human genetic variants in L-FABP gene are also associated with lipid metabolic abnormalities [10;11;22;60-63;94-97]; iii) acyl CoA binding protein (ACBP) which exclusively binds LCFA-CoA and facilitates ACAT-2-mediated esterification in the endoplasmic reticulum [26;98-100]. While studies with individually ablated SCP-2/SCP-x or L-FABP genes have been informative, impact on phenotype interpretations of many SCP-2/SCP-x gene-ablated mouse studies have been complicated by concomitant upregulation of L-FABP [66-68].…”

“…While neither SCP-2 nor L-FABP have intrinsic enzymatic activity, in vitro studies show that both SCP-2 and L-FABP: i) bind cholesterol [15-18]; ii) bind LCFA-CoA [19-22]; iii) enhance LCFA-CoA transacylation to cholesterol by microsomal ACAT-2, the rate limiting enzymes in cholesteryl ester synthesis in vitro [23-26] and in cultured fibroblasts overexpressing the respective proteins [27;28]; iii) enhance LCFA-CoA transacylation to glycerol-3-phosphate by microsomal glycerol-3-phosphate acyltransferase (GPAT/GPAM), the rate limiting enzyme in glyceride (phospholipid, triglyceride) synthesis [29-31]. Conversely, both SCP-2 and L-FABP also stimulate carnitine palmitoyl acyl transferase I (CPT1)-mediated LCFA-CoA transacylation in the outer mitochondrial membrane to facilitate LCFA β-oxidation [32].…”