The Human FA2H Gene Encodes a Fatty Acid 2-Hydroxylase

Abstract

2-Hydroxysphingolipids are a subset of sphingolipids containing 2-hydroxy fatty acids. The 2-hydroxylation occurs during de novo ceramide synthesis and is catalyzed by fatty acid 2-hydroxylase (also known as fatty acid ␣-hydroxylase). In mammals, 2-hydroxysphingolipids are present abundantly in brain because the major myelin lipids galactosylceramides and sulfatides contain 2-hydroxy fatty acids. Here we report identification and characterization of a human gene that encodes a fatty acid 2-hydroxylase. Data base searches revealed a human homologue of the yeast ceramide 2-hydroxylase gene (FAH1), which we named FA2H. The FA2H gene encodes a 372-amino acid protein with 36% identity and 46% similarity to yeast Fah1p. The amino acid sequence indicates that FA2H protein contains an N-terminal cytochrome b 5 domain and four potential transmembrane domains. FA2H also contains the iron-binding histidine motif conserved among membrane-bound desaturases/ hydroxylases. COS7 cells expressing human FA2H contained 3-20-fold higher levels of 2-hydroxyceramides (C16, C18, C24, and C24:1) and 2-hydroxy fatty acids compared with control cells. Microsomal fractions prepared from transfected COS7 cells showed tetracosanoic acid 2-hydroxylase activities in an NADPH-and NADPH: cytochrome P-450 reductase-dependent manner. FA2H lacking the N-terminal cytochrome b 5 domain had little activity, indicating that this domain is a functional component of this enzyme. Northern blot analysis showed that the FA2H gene is highly expressed in brain and colon tissues. These results demonstrate that the human FA2H gene encodes a fatty acid 2-hydroxylase. FA2H is likely involved in the formation of myelin 2-hydroxy galactosylceramides and -sulfatides.Sphingolipids are a large class of lipids found in all eukaryotic cells and are involved in a variety of cellular processes. The structural diversity of sphingolipids stems from over 300 known distinct head groups as well as modifications of the hydrophobic ceramide moiety. One of the common modifications of the ceramide moiety is 2-hydroxylation of the N-acyl chain. Sphingolipids with 2-hydroxy fatty acid are found in most organisms including plants, yeast, worms, vertebrate animals, and some bacterial species.In mammals, 2-hydroxy fatty acid-containing sphingolipids are uniquely abundant in nervous and epidermal tissues. In mammalian central and peripheral nervous systems, galactosylceramides and sulfatides (3-sulfate ester of galactosylceramide) are major lipid components of myelin (1, 2). These glycosphingolipids contain a high proportion (ϳ50%) of 2-hydroxy fatty acid (3) and are critical components of myelin (4, 5). In mammalian epidermal tissues, there are several unique, very long chain ceramides with 2-hydroxy fatty acids, which are critical for the permeability barrier function of epidermis (6, 7).Several biophysical studies (8 -10) demonstrated that the 2-hydroxyl group in sphingolipids has a profound effect in the lipid organization within membranes because of its hydrogenbonding capability....

Breakdown of 2-Hydroxylated Straight Chain Fatty Acids via Peroxisomal 2-Hydroxyphytanoyl-CoA Lyase

“…Regardless of this discrepancy, a recently described fatty acid 2-hydroxylase, highly abundant in brain and encoded by the FA2H gene (18), is likely responsible for the formation of 2-hydroxyfatty acids in man.…”

The Crystal Structure of an Integral Membrane Fatty Acid α-Hydroxylase

“…GalCer is generated from a ceramide-based precursor composed of a long chain base (LCB) moiety that is derived from palmitoyl-CoA and a very long chain fatty acid (VLCFA) moiety that is typically 26 carbons long (2). Over 50% of GalCer and sulfatide within the myelin sheath are hydroxylated at C-2 of the VLCFA moiety by the enzyme FA2H (3,4). No other mammalian tissues contain such high levels of hydroxylated lipid.…”

Phytosphingosine degradation pathway includes fatty acid α-oxidation reactions in the endoplasmic reticulum

“…The FA 2-hydroxylase FA2H directly forms 2-OH FAs from FAs (12,17). Although the PHS degradation pathway generates 2-OH C16:0-COOH almost exclusively, FA2H can produces 2-OH FAs ranging from long chain to very long chain (17,41).…”

“…The FA 2-hydroxylase FA2H directly forms 2-OH FAs from FAs (12,17). Although the PHS degradation pathway generates 2-OH C16:0-COOH almost exclusively, FA2H can produces 2-OH FAs ranging from long chain to very long chain (17,41). 2-OH very long-chain FAs with C22 or C24 chain length exist abundantly in galactosylceramides and sulfatides in myelin and are important for myelin function and maintenance (16,(18)(19)(20).…”

“…Their 2-OH groups are important for the formation and maintenance of the myelin sheath, which is composed of a multilayered lipid structure, probably by enhancing lipid-lipid interactions via hydrogen bonds. The FA 2-hydroxylase FA2H catalyzes conversion of FAs to 2-OH FAs (12,17). Reflecting the importance of the 2-OH groups of galactosylceramide and sulfatide in myelin, FA2H mutations cause hereditary spastic paraplegia in human (18, 19) and late-onset axon and myelin sheath degeneration in mice (16,20).…”