The human fatty acid-binding protein family: Evolutionary divergences and functions
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The human fatty acid-binding protein family: Evolutionary divergences and functions Rebecca L . Smathers and Dennis R. Petersen* Molecular Toxicology and Environmental Health Sciences Program, Department of Pharmaceutical Sciences, University of Colorado Denver, Aurora, CO 80045, USA *Correspondence to: Tel: þ1 303 724 3397; Fax: þ1 303 724 7266; E-mail: [email protected] Date received (in revised form): 19th January 2011
Abstract Fatty acid-binding proteins (FABPs) are members of the intracellular lipid-binding protein (iLBP) family and are involved in reversibly binding intracellular hydrophobic ligands and trafficking them throughout cellular compartments, including the peroxisomes, mitochondria, endoplasmic reticulum and nucleus. FABPs are small, structurally conserved cytosolic proteins consisting of a water-filled, interior-binding pocket surrounded by ten anti-parallel beta sheets, forming a beta barrel. At the superior surface, two alpha-helices cap the pocket and are thought to regulate binding. FABPs have broad specificity, including the ability to bind long-chain (C16–C20) fatty acids, eicosanoids, bile salts and peroxisome proliferators. FABPs demonstrate strong evolutionary conservation and are present in a spectrum of species including Drosophila melanogaster, Caenorhabditis elegans, mouse and human. The human genome consists of nine putatively functional protein-coding FABP genes. The most recently identified family member, FABP12, has been less studied. Keywords: FABP, intracellular lipid-binding proteins, uptake and trafficking of lipids, metabolic diseases, human genome
Introduction Hydrophobic ligands, such as fatty acids (FAs) and their acyl-CoA derivatives (FA-CoA), serve many biological functions within the cell. They serve as metabolic energy sources, substrates for membranes and signalling molecules for metabolic regulation.1,2 The insoluble properties of FAs make for the requirement for chaperones to bind and transfer them throughout various cellular compartments, including the peroxisomes, mitochondria, endoplasmic reticulum, lipid droplets and nucleus. A family of highly expressed intracellular lipid-binding proteins (iLBPs)—the fatty acid-binding proteins (FABPs)—serves to bind these free ligands with high affinity. FABPs are ubiquitously expressed throughout tissues that are highly active in FA
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metabolism and comprise several isoforms. To date, nine FABP protein-coding genes have been identified in the human genome. These include liver(L-FABP), intestine- (I-FABP), heart- (H-FABP), adipocyte- (A-FABP), epidermal- (E-FABP), ileal(Il-FABP), brain- (B-FABP), myelin- (M-FABP) and testis-FABP (T-FABP). These different isoforms were first named for the organ in which they were first identified or mostly predominate, but their expression profiles are not exclusive to that specific organ. For example, L-FABP is not only expressed in the liver, but also in the intestine, pancreas, kidney, lung and stomach. In addition to the nine known FABPs that have been widely studied, a ne
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