Acyl-CoA:Lysophospholipid Acyltransferases

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Platelet-activating factor (PAF) is a potent proinflammatory phospholipid mediator that elicits various cellular functions under physiological and pathological conditions. We have recently identified two enzymes involved in PAF production: lysophosphatidylcholine acyltransferase-1 (LPCAT1) and LPCAT2. We found that LPCAT2 is highly expressed in inflammatory cells and is activated by lipopolysaccharide (LPS) treatment through Toll-like receptor 4. However, the molecular mechanism for the activation remains elusive. In this study, Phos-tag SDS-PAGE revealed the LPS-induced phosphorylation of LPCAT2. Furthermore, mass spectrometry and mutagenesis analyses identified Ser 34 of LPCAT2 as the phosphorylation site to enhance the catalytic activities. The experiments using inhibitors and siRNA against MAPK cascades demonstrated that LPCAT2 phosphorylation through LPS-TLR4 signaling may directly depend on MAPK-activated protein kinase 2 (MAPKAP kinase 2 or MK2). These findings develop a further understanding of both PAF production and phospholipid remodeling triggered by inflammatory stimuli. Specific inhibition of the PAF biosynthetic activity by phosphorylated LPCAT2 will provide a novel target for the regulation of inflammatory disorders.

Section: Discussionmentioning

confidence: 99%

“…This biosynthetic pathway of phospholipids, known as Lands' cycle or remodeling pathway, is responsible for generating the membrane diversity (16). PUFAs in phospholipids may affect membrane curvature and fluidity and store lipid mediator precursors that are converted to eicosanoids, such as prostaglandins, leukotrienes, and lipoxins (1).…”

mentioning

confidence: 99%

Phosphorylation of Lysophosphatidylcholine Acyltransferase 2 at Ser34 Enhances Platelet-activating Factor Production in Endotoxin-stimulated Macrophages

Morimoto

Shindou

Oda

et al. 2010

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“…1). Both of these subfamilies contain numerous members in humans, yeast, and bacteria and are characterized by the presence of four conserved sequence motifs comprised within a 100 -150-amino acid-long acyltransferase domain defined by PF01553 (Pfam), COG0204, or COG2937 (NCBI) (1,22,23). The acyltransferase family defined by PF01553 also contains the Escherichia coli GPAT PlsB, the E. coli LPAAT PlsC, and 14 human genes encoding enzymes with either GPAT (human GPAT1 to GPAT4), lysophospholipid acyltransferase, or unknown activities (22)(23)(24)(25)(26).…”

mentioning

confidence: 99%

Topology of 1-Acyl-sn-glycerol-3-phosphate Acyltransferases SLC1 and ALE1 and Related Membrane-bound O-Acyltransferases (MBOATs) of Saccharomyces cerevisiae

Pagac

Mora

Duperrex

et al. 2011

Background:The active sites of bacterial and mammalian 1-acyl-sn-glycerol-3-phosphate acyltransferases are assumed to reside in the cytosol. Results: The topology of yeast 1-acyl-sn-glycerol-3-phosphate acyltransferases has been determined. Their most conserved residues and motifs are located in the ER lumen. Conclusion: Biosynthesis of phosphatidic acid in yeast may occur on the lumenal side of the ER. Significance: The data invite additional, complementary experimentation.

“…Lyso-GPL acyltransferases play an important role in Land's cycle of acyl chain remodeling (28,38,47). With the identification of AT1G78690 as a lyso-GPL acyltransferase, its role in relation to the other lyso-GPL acyltransferases of A. thaliana (38) needs to be determined.…”

Section: Discussionmentioning

confidence: 99%

Putative N-Acylphosphatidylethanolamine Synthase from Arabidopsis thaliana Is a Lysoglycerophospholipid Acyltransferase

Bulat

Garrett

2011

AT1G78690, a gene found in Arabidopsis thaliana, has been reported to encode a N-acyltransferase that transfers an acyl chain from acyl-CoA to the headgroup of phosphatidylethanolamine (PE) to form N-acylphosphatidylethanolamine (N-acyl-PE). Our investigation suggests that At1g78690p is not a PE-dependent N-acyltransferase but is instead a lysoglycerophospholipid O-acyltransferase. We overexpressed AT1G78690 in Escherichia coli, extracted the cellular lipids, and identified the accumulating glycerophospholipid as acylphos- phatidylglycerol (acyl-PG). Electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-MS) analysis yielded [M ؊ H]؊ ions, corresponding by exact mass to acyl-PG rather than N-acyl-PE. Collision-induced dissociation mass spectrometry (MS/MS) yielded product ions consistent with acyl-PG. In addition, in vitro enzyme assays using both 32 P-and 14 C-radiolabeled substrates showed that AT1G78690 acylates 1-acyllysophosphatidylethanolamine (1-acyllyso-PE) and 1-acyllysophosphatidylglycerol (1-acyllyso-PG), but not PE or phosphatidylglycerol (PG), to form a diacylated product that co-migrates with PE and PG, respectively. We analyzed the diacylated product formed by AT1G78690 using a combination of base hydrolysis, phospholipase D treatment, ESI-MS, and MS/MS to show that AT1G78690 acylates the sn-2-position of 1-acyllyso-PE and 1-acyllyso-PG. N-Acylphosphatidylethanolamine (N-acyl-PE)2 is an anionic minor membrane glycerophospholipid (GPL) that is abundant in animals, higher plants, and certain microorganisms, such as yeast and Escherichia coli (1-7). This GPL is of particular interest because of its well documented role as the precursor to N-acylethanolamines (NAEs), a class of bioactive lipids that are involved in a variety of physiological processes, such as responses to pathogens, plant development, and germination in plants (8 -10) as well as control of appetite, inflammation, and apoptosis (11-13) in animals.In animals, N-acyl-PE synthesis is catalyzed by two distinct biochemical activities. A Ca 2ϩ -dependent membrane-associated protein has been characterized in brain, testis, and heart (14). This enzyme has been shown to catalyze the transfer of an acyl chain from the sn-1-position of a diacylated GPL, functions most efficiently at alkaline pH, and requires divalent cations (13,15,16). The gene encoding this enzyme has yet to be identified.A lecithin retinol acyltransferase-like protein from rats, RLP-1, has been shown to encode a Ca 2ϩ -independent N-acyltransferase (NAT) (17). It is predominantly expressed in testis and is, therefore, thought to be distinct from the Ca 2ϩ -dependent NAT. Ca 2ϩ -independent NAT activity is detected in both the soluble and membrane fractions when overexpressed in COS-7 cells and does not show preference for transfer of the sn-1 or sn-2 acyl chain to the amine of PE (17). Human and mouse homologs have been cloned and shown to possess similar NAT activity (18).In plants, N-acyl-PE is proposed to be synthesized from PE and unesterified fatty acid...