1
|
Structural basis of the acyl-transfer mechanism of human GPAT1. Nat Struct Mol Biol 2023; 30:22-30. [PMID: 36522428 DOI: 10.1038/s41594-022-00884-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 10/31/2022] [Indexed: 12/23/2022]
Abstract
Glycerol-3-phosphate acyltransferase (GPAT)1 is a mitochondrial outer membrane protein that catalyzes the first step of de novo glycerolipid biosynthesis. Hepatic expression of GPAT1 is linked to liver fat accumulation and the severity of nonalcoholic fatty liver diseases. Here we present the cryo-EM structures of human GPAT1 in substrate analog-bound and product-bound states. The structures reveal an N-terminal acyltransferase domain that harbors important catalytic motifs and a tightly associated C-terminal domain that is critical for proper protein folding. Unexpectedly, GPAT1 has no transmembrane regions as previously proposed but instead associates with the membrane via an amphipathic surface patch and an N-terminal loop-helix region that contains a mitochondrial-targeting signal. Combined structural, computational and functional studies uncover a hydrophobic pathway within GPAT1 for lipid trafficking. The results presented herein lay a framework for rational inhibitor development for GPAT1.
Collapse
|
2
|
Stone SJ. Mechanisms of intestinal triacylglycerol synthesis. Biochim Biophys Acta Mol Cell Biol Lipids 2022; 1867:159151. [PMID: 35296424 DOI: 10.1016/j.bbalip.2022.159151] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 01/13/2022] [Accepted: 02/16/2022] [Indexed: 02/07/2023]
Abstract
Triacylglycerols are a major source of stored energy that are obtained either from the diet or can be synthesized to some extent by most tissues. Alterations in pathways of triacylglycerol metabolism can result in their excessive accumulation leading to obesity, insulin resistance, cardiovascular disease and nonalcoholic fatty liver disease. Most tissues in mammals synthesize triacylglycerols via the glycerol 3-phosphate pathway. However, in the small intestine the monoacylglycerol acyltransferase pathway is the predominant pathway for triacylglycerol biosynthesis where it participates in the absorption of dietary triacylglycerol. In this review, the enzymes that are part of both the glycerol 3-phosphate and monoacylglycerol acyltransferase pathways and their contributions to intestinal triacylglycerol metabolism are reviewed. The potential of some of the enzymes involved in triacylglycerol synthesis in the small intestine as possible therapeutic targets for treating metabolic disorders associated with elevated triacylglycerol is briefly discussed.
Collapse
Affiliation(s)
- Scot J Stone
- Department of Biochemistry, Microbiology and Immunology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada.
| |
Collapse
|
3
|
Miyata N, Kuge O. Topology of phosphatidylserine synthase 1 in the endoplasmic reticulum membrane. Protein Sci 2021; 30:2346-2353. [PMID: 34516042 DOI: 10.1002/pro.4182] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 09/02/2021] [Accepted: 09/07/2021] [Indexed: 12/28/2022]
Abstract
Phosphatidylserine (PS) synthase 1 (PSS1) of mammalian cells is a multiple membrane-spanning protein of the endoplasmic reticulum (ER) and regulated by inhibition with the product PS. Alanine-scanning mutagenesis of PSS1 has revealed eight amino acid residues as those crucial for its activity and six as those important for its regulation. Furthermore, three missense mutations in the human PSS1 gene, which lead to regulatory dysfunctions of PSS1 and are causative of Lenz-Majewski syndrome, have been identified. In this study, we investigated the membrane topology of PSS1 by means of epitope insertion and immunofluorescence. According to a 10-transmembrane segment model supported by topology analysis of PSS1, all the 8 amino acid residues crucial for the enzyme activity were localized to the luminal side of the lipid bilayer or the lumen of the ER, whereas all the 9 amino acid residues involved in the enzyme regulation were localized to the cytosol or the cytoplasmic side of the lipid bilayer of the ER. This localization of the functional amino acid residues suggests that PSS1 is regulated by inhibition with PS in the cytoplasmic leaflet of the ER membrane and synthesizes PS at the luminal leaflet.
Collapse
Affiliation(s)
- Non Miyata
- Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan
| | - Osamu Kuge
- Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan
| |
Collapse
|
4
|
Horibata Y, Mitsuhashi S, Shimizu H, Maejima S, Sakamoto H, Aoyama C, Ando H, Sugimoto H. The phosphatidylcholine transfer protein StarD7 is important for myogenic differentiation in mouse myoblast C2C12 cells and human primary skeletal myoblasts. Sci Rep 2020; 10:2845. [PMID: 32071354 PMCID: PMC7029042 DOI: 10.1038/s41598-020-59444-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 01/27/2020] [Indexed: 01/05/2023] Open
Abstract
StarD7 is a phosphatidylcholine (PC)-specific lipid transfer protein essential for the maintenance of mitochondrial PC composition, morphogenesis, and respiration. Here, we studied the role of StarD7 in skeletal myoblast differentiation using mouse myoblast C2C12 cells and human primary myoblasts. Immunofluorescence and immuno-electron microscopy revealed that StarD7 was distributed in the cytosol, inner mitochondria space, and outer leaflet of the outer mitochondrial membrane in C2C12 cells. Unlike human kidney embryonic cell line HEK293 cells, the mitochondrial proteinase PARL was not involved in the processing and maturation of StarD7 in C2C12 cells. StarD7 was constantly expressed during myogenic differentiation of C2C12 cells. The siRNA-mediated knockdown of StarD7 in C2C12 cells and human primary myoblasts significantly impaired myogenic differentiation and reduced the expression of myomaker, myomerger and PGC-1α. The reduction in mitochondrial PC levels and oxygen consumption rates, decreased expression of myomaker, myomerger and PGC-1α, as well as impaired myogenic differentiation, were completely restored when the protein was reintroduced into StarD7-knockout C2C12 cells. These results suggest that StarD7 is important for skeletal myogenesis in mammals.
Collapse
Affiliation(s)
- Yasuhiro Horibata
- Department of Biochemistry, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu, Tochigi, 321-0293, Japan
| | - Satomi Mitsuhashi
- Department of Human Genetics, Yokohama City University Graduate School of Medicine, Fukuura 3-9, Kanazawa-ku, Yokohama, 236-0004, Japan
| | - Hiroaki Shimizu
- Department of Biochemistry, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu, Tochigi, 321-0293, Japan
| | - Sho Maejima
- Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama, 701-4303, Japan
| | - Hirotaka Sakamoto
- Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama, 701-4303, Japan
| | - Chieko Aoyama
- Department of Biochemistry, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu, Tochigi, 321-0293, Japan
| | - Hiromi Ando
- Department of Biochemistry, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu, Tochigi, 321-0293, Japan
| | - Hiroyuki Sugimoto
- Department of Biochemistry, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu, Tochigi, 321-0293, Japan.
| |
Collapse
|
5
|
Zhu W, Guo Q, Cheng Y, Wu X. Identification and functional expression of two subtypes of glycerol-3-phosphate acyltransferase differently regulating triacylglyceride synthesis during ovary development in Chinese mitten crab, Eriocheir sinensis. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2019; 331:494-505. [PMID: 31436894 DOI: 10.1002/jez.2316] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 08/01/2019] [Indexed: 01/09/2023]
Abstract
Triacylglycerides (TAG) are a pivotal nutrient for crustacean reproduction, rapidly accumulating in gonads and hepatopancreas during the ovary development. Glycerol-3-phosphate acyltransferase (GPAT) is the enzyme catalyzing the first step in TAG synthesis. In the present study, two EsGPATs subtypes (EsGPAT1 and EsGPAT2) were identified and characterized. The transcript of EsGPAT1 was highly expressed in thoracic ganglia, hepatopancreas and ovary, while EsGPAT2 was mainly detected in nervous tissues and intestine. During the ovary development, in hepatopancreas, the expression levels of EsGPAT1 increased from Stage I to its maximum at Stage IV and then declined sharply. The transcription levels of EsGPAT2 were highest at Stage I and then gradually declined to reach its minimum at Stage IV. In ovaries, the EsGPAT1 expression levels increased from Stage I to reach its maximum at Stage IV and then declined. The transcription levels of EsGPAT2 reached the peak at Stage I and then declined to the minimum at Stage III. In situ hybridization revealed they were both located in the F cells and R cells of hepatopancreas and all types of cells at Stage I, the follicle cells and the exogenous vitellogenic oocytes at Stage III and nearly mature oocytes at Stage IV of the ovary. In addition, the knockdown of EsGPAT1 downregulated the expression levels of downstream genes in TAG synthesis pathway, but it was not observed in RNAi treatment group of EsGPAT2. These results indicate that the two EsGPATs identified have different roles in TAG metabolism during the ovarian development of E. sinensis.
Collapse
Affiliation(s)
- Wangling Zhu
- Centre for Research on Environmental Ecology and Fish Nutrition of the Ministry of Agriculture, Shanghai Ocean University, Shanghai, China.,Key Laboratory of Freshwater Aquatic Genetic Resources, Ministry of Agriculture, Shanghai Ocean University, Shanghai, China
| | - Qing Guo
- Centre for Research on Environmental Ecology and Fish Nutrition of the Ministry of Agriculture, Shanghai Ocean University, Shanghai, China.,Key Laboratory of Freshwater Aquatic Genetic Resources, Ministry of Agriculture, Shanghai Ocean University, Shanghai, China
| | - Yongxu Cheng
- Centre for Research on Environmental Ecology and Fish Nutrition of the Ministry of Agriculture, Shanghai Ocean University, Shanghai, China.,Key Laboratory of Freshwater Aquatic Genetic Resources, Ministry of Agriculture, Shanghai Ocean University, Shanghai, China
| | - Xugan Wu
- Centre for Research on Environmental Ecology and Fish Nutrition of the Ministry of Agriculture, Shanghai Ocean University, Shanghai, China.,Shanghai Collaborative Innovation Centre for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai, China
| |
Collapse
|
6
|
Transcriptional Regulation of Acyl-CoA:Glycerol- sn-3-Phosphate Acyltransferases. Int J Mol Sci 2019; 20:ijms20040964. [PMID: 30813330 PMCID: PMC6412627 DOI: 10.3390/ijms20040964] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 02/14/2019] [Accepted: 02/15/2019] [Indexed: 12/13/2022] Open
Abstract
Acyl-CoA:glycerol-sn-3-phosphate acyltransferase (GPAT) is an enzyme responsible for the rate-limiting step in the synthesis of glycerophospholipids and triacylglycerol (TAG). The enzymes of mammalian species are classified into four isoforms; GPAT1 and GPAT2 are localized in the mitochondrial outer membrane, whereas GPAT3 and GPAT4 are localized in the endoplasmic reticulum membrane. The activity of each enzyme expressed is associated with physiological and pathological functions. The transcriptional regulation is well known, particularly in GPAT1. GPAT1 mRNA expression is mainly regulated by the binding of the transcriptional factor SREBP-1c to the specific element (the sterol regulatory element) flanking the GPAT1 promoter. The TAG level is controlled by the insulin-induced transcriptional expression of GPAT1, which occupies most of the GPAT activity in the liver. The transcriptional regulation of the other three GPAT isoforms remains undetermined in detail. It is predicted that retinoic acid serves as a transcription factor in the GPAT2 promoter. PPARγ (peroxisome proliferator-activated receptor γ) increases the mRNA expression of GPAT3, which is associated with TAG synthesis in adipose tissues. Although GPAT has been considered to be a key enzyme in the production of TAG, unexpected functions have recently been reported, particularly in GPAT2. It is likely that GPAT2 is associated with tumorigenesis and normal spermatogenesis. In this review, the physiological and pathophysiological roles of the four GPAT isoforms are described, alongside the transcriptional regulation of these enzymes.
Collapse
|
7
|
Keenan KA, Grove TJ, Oldham CA, O'Brien KM. Characterization of mitochondrial glycerol-3-phosphate acyltransferase in notothenioid fishes. Comp Biochem Physiol B Biochem Mol Biol 2016; 204:9-26. [PMID: 27836743 DOI: 10.1016/j.cbpb.2016.11.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2016] [Revised: 10/27/2016] [Accepted: 11/03/2016] [Indexed: 10/20/2022]
Abstract
Hearts of Antarctic icefishes (suborder Notothenioidei, family Channichthyidae) have higher densities of mitochondria, and mitochondria have higher densities of phospholipids, compared to red-blooded notothenioids. Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the rate-limiting step in glycerolipid biosynthesis. There are four isoforms of GPAT in vertebrates; GPAT1 and GPAT2 are localized to the outer mitochondrial membrane, whereas GPAT3 and GPAT4 are localized to the endoplasmic reticulum membrane. We hypothesized that transcript levels of GPAT1 and/or GPAT2 would mirror densities of mitochondrial phospholipids and be higher in the icefish Chaenocephalus aceratus compared to the red-blooded species Notothenia coriiceps. Transcript levels of GPAT1 were quantified in heart ventricles and liver using qRT-PCR. Additionally, GPAT1 cDNA was sequenced in the Antarctic notothenioids, C. aceratus and N. coriiceps, and in the sub-Antarctic notothenioid, Eleginops maclovinus, to identify amino acid substitutions that may maintain GPAT1 function at cold temperature. Transcript levels of GPAT1 were higher in liver compared to heart ventricles but were not significantly different between the two species. In contrast, transcripts of GPAT2 were only detected in ventricle where they were 6.6-fold higher in C. aceratus compared to N. coriiceps. These data suggest GPAT1 may be more important for synthesizing triacylglycerol, whereas GPAT2 may regulate synthesis of phospholipids. GPAT1 amino acid sequences are highly conserved among the three notothenioids with 97.9-98.7% identity. Four amino acid substitutions within the cytosolic region of Antarctic notothenioid GPAT1 may maintain conformational changes necessary for binding and catalysis at cold temperature.
Collapse
Affiliation(s)
- Kelly A Keenan
- University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775, United States
| | - Theresa J Grove
- Department of Biology, Valdosta State University, Valdosta, GA 31698, United States
| | - Corey A Oldham
- University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775, United States
| | - Kristin M O'Brien
- University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775, United States.
| |
Collapse
|
8
|
Gonzalez-Baro MR, Coleman RA. Mitochondrial acyltransferases and glycerophospholipid metabolism. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:49-55. [PMID: 27377347 DOI: 10.1016/j.bbalip.2016.06.023] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Revised: 06/23/2016] [Accepted: 06/28/2016] [Indexed: 12/14/2022]
Abstract
Our understanding of the synthesis and remodeling of mitochondrial phospholipids remains incomplete. Two isoforms of glycerol-3-phosphate acyltransferase (GPAT1 and 2) and two isoforms of acylglycerol-3-phosphate acyltransferase (AGPAT4 and 5) are located on the outer mitochondrial membrane, suggesting that both lysophosphatidic acid and phosphatidic acid are synthesized in situ for de novo glycerolipid biosynthesis. However, it is believed that the phosphatidic acid substrate for cardiolipin and phosphatidylethanolamine biosynthesis is produced at the endoplasmic reticulum whereas the phosphatidic acid synthesized in the mitochondria must be transferred to the endoplasmic reticulum before it undergoes additional steps to form the mature phospholipids that are trafficked back to the mitochondria. It is unclear whether mitochondrial phospholipids are remodeled by mitochondrial acyltransferases or whether lysophospholipids must return to the endoplasmic reticulum or to the mitochondrial associated membrane for reesterification. In this review we will focus on the few glycerolipid acyltransferases that are known to be mitochondrial. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.
Collapse
Affiliation(s)
- Maria R Gonzalez-Baro
- Instituto de Investigaciones Bioquımicas de La Plata, CONICET, Facultad de Ciencias Medicas, Universidad Nacional de La Plata, La Plata 1900, Argentina
| | - Rosalind A Coleman
- Department of Nutrition, University of North Carolina, Chapel Hill, NC 27599, USA.
| |
Collapse
|
9
|
Patel N, Pirani KA, Zhu T, Cheung-See-Kit M, Lee S, Chen DG, Zufferey R. The Glycerol-3-Phosphate Acyltransferase TbGAT is Dispensable for Viability and the Synthesis of Glycerolipids in Trypanosoma brucei. J Eukaryot Microbiol 2016; 63:598-609. [PMID: 26909872 DOI: 10.1111/jeu.12309] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Revised: 01/30/2016] [Accepted: 02/16/2016] [Indexed: 01/09/2023]
Abstract
Glycerolipids are the main constituents of biological membranes in Trypanosoma brucei, which causes sleeping sickness in humans. Importantly, they occur as a structural component of the glycosylphosphatidylinositol lipid anchor of the abundant cell surface glycoproteins procyclin in procyclic forms and variant surface glycoprotein in bloodstream form, that play crucial roles for the development of the parasite in the insect vector and the mammalian host, respectively. The present work reports the characterization of the glycerol-3-phosphate acyltransferase TbGAT that initiates the biosynthesis of ester glycerolipids. TbGAT restored glycerol-3-phosphate acyltransferase activity when expressed in a Leishmania major deletion strain lacking this activity and exhibited preference for medium length, unsaturated fatty acyl-CoAs. TbGAT localized to the endoplasmic reticulum membrane with its N-terminal domain facing the cytosol. Despite that a TbGAT null mutant in T. brucei procyclic forms lacked glycerol-3-phosphate acyltransferase activity, it remained viable and exhibited similar growth rate as the wild type. TbGAT was dispensable for the biosynthesis of phosphatidylcholine, phosphatidylinositol, phosphatidylserine, and GPI-anchored protein procyclin. However, the null mutant exhibited a slight decrease in phosphatidylethanolamine biosynthesis that was compensated with a modest increase in production of ether phosphatidylcholine. Our data suggest that an alternative initial acyltransferase takes over TbGAT's function in its absence.
Collapse
Affiliation(s)
- Nipul Patel
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439
| | - Karim A Pirani
- Department of Biochemistry, Kansas State University, Manhattan, Kansas, 66506
| | - Tongtong Zhu
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439
| | - Melanie Cheung-See-Kit
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439
| | - Sungsu Lee
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439
| | - Daniel G Chen
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439
| | - Rachel Zufferey
- Department of Biological Sciences, St John's University, 8000 Utopia Parkway, Jamaica, New York, 11439.,Department of Biochemistry, Kansas State University, Manhattan, Kansas, 66506
| |
Collapse
|
10
|
Zhang Y, Liu X, Bai J, Tian X, Zhao X, Liu W, Duan X, Shang W, Fan HY, Tong C. Mitoguardin Regulates Mitochondrial Fusion through MitoPLD and Is Required for Neuronal Homeostasis. Mol Cell 2016; 61:111-24. [DOI: 10.1016/j.molcel.2015.11.017] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 10/12/2015] [Accepted: 11/09/2015] [Indexed: 11/30/2022]
|
11
|
Identification and characterization of a gene encoding a putative lysophosphatidyl acyltransferase from Arachis hypogaea. J Biosci 2013; 37:1029-39. [PMID: 23151793 DOI: 10.1007/s12038-012-9277-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Lysophosphatidyl acyltransferase (LPAT) is the important enzyme responsible for the acylation of lysophosphatidic acid (LPA), leading to the generation of phosphatidic acid (PA) in plant. Its encoding gene is an essential candidate for oil crops to improve oil composition and increase seed oil content through genetic engineering. In this study, a full length AhLPAT4 gene was isolated via cDNA library screening and rapid amplification of cDNA ends (RACE); our data demonstrated that AhLPAT4 had 1631 nucleotides, encoding a putative 43.8 kDa protein with 383 amino acid residues. The deduced protein included a conserved acyltransferase domain and four motifs (I–IV) with putative LPA and acyl-CoA catalytic and binding sites. Bioinformatic analysis indicated that AhLPAT4 contained four transmembrane domains (TMDs), localized to the endoplasmic reticulum (ER) membrane; detailed analysis indicated that motif I and motifs II–III in AhLPAT4 were separated by the third TMD, which located on cytosolic and ER luminal side respectively, and hydrophobic residues on the surface of AhLPAT4 protein fold to form a hydrophobic tunnel to accommodate the acyl chain. Subcellular localization analysis confirmed that AhLPAT4 was a cytoplasm protein.Phylogenetic analysis revealed that AhLPAT4 had a high homology (63.7–78.3%) with putative LPAT4 proteins from Glycine max, Arabidopsis thaliana and Ricinus communis. AhLPAT4 was ubiquitously expressed in diverse tissues except in flower, which is almost undetectable. The expression analysis in different developmental stages in peanut seeds indicated that AhLPAT4 did not coincide with oil accumulation.
Collapse
|
12
|
Pagac M, Vazquez HM, Bochud A, Roubaty C, Knöpfli C, Vionnet C, Conzelmann A. Topology of the microsomal glycerol-3-phosphate acyltransferase Gpt2p/Gat1p ofSaccharomyces cerevisiae. Mol Microbiol 2012; 86:1156-66. [DOI: 10.1111/mmi.12047] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/18/2012] [Indexed: 02/06/2023]
Affiliation(s)
- Martin Pagac
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Hector M. Vazquez
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Arlette Bochud
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Carole Roubaty
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Cécile Knöpfli
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Christine Vionnet
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| | - Andreas Conzelmann
- Department of Biology; University of Fribourg; CH-1700; Fribourg; Switzerland
| |
Collapse
|
13
|
Bertolesi GE, Iannattone S, Johnston J, Zaremberg V, McFarlane S. Identification and expression analysis of GPAT family genes during early development of Xenopus laevis. Gene Expr Patterns 2012; 12:219-27. [PMID: 22564474 DOI: 10.1016/j.gep.2012.04.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Revised: 03/27/2012] [Accepted: 04/10/2012] [Indexed: 11/27/2022]
Abstract
Production of lysophosphatidic acid (LPA) is the first step in the de novo pathway for glycerolipid biosynthesis, which is mainly catalyzed by the glycerol-3-phosphate acyltransferases (GPATs; EC2.3.1.15). DHAPAT (EC2.3.1.42) also contributes in a minor way, using dihydroxyacetone phosphate as substrate. Final products and intermediates of the glycerolipid synthesis pathway are the main structural components of cellular membranes, and provide signalling molecules that regulate diverse biological processes, including cell proliferation, differentiation and growth. Here we identified the four orthologs of the mammalian GPATs (1-4) and DHAPAT in Xenopus, including a novel, short variant of GPAT2, and analyzed their expression pattern during embryonic development. Xenopus GPAT1/2 localized to mitochondria, while GPAT3/4 associated with the endoplasmic reticulum. All are similarly expressed in the early embryonic nervous system. A more tissue specific pattern emerges during organogenesis, including liver expression for GPAT1/4, and testis expression for GPAT2. All acyltransferases were expressed in kidney, though GPAT3 was excluded from the pronephric ducts. Our results suggest important roles of GPATs and DHAPAT during early organogenesis.
Collapse
Affiliation(s)
- Gabriel E Bertolesi
- Hotchkiss Brain Institute, Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada T2N 4N1
| | | | | | | | | |
Collapse
|
14
|
Membrane topology of murine glycerol-3-phosphate acyltransferase 2. Biochem Biophys Res Commun 2012; 418:506-11. [DOI: 10.1016/j.bbrc.2012.01.055] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Accepted: 01/11/2012] [Indexed: 10/14/2022]
|
15
|
Coleman RA, Mashek DG. Mammalian triacylglycerol metabolism: synthesis, lipolysis, and signaling. Chem Rev 2011; 111:6359-86. [PMID: 21627334 PMCID: PMC3181269 DOI: 10.1021/cr100404w] [Citation(s) in RCA: 206] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Rosalind A Coleman
- Department of Nutrition, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
| | | |
Collapse
|
16
|
Kerner J, Lee K, Hoppel CL. Post-translational modifications of mitochondrial outer membrane proteins. Free Radic Res 2010; 45:16-28. [DOI: 10.3109/10715762.2010.515218] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
|
17
|
Gidda SK, Shockey JM, Rothstein SJ, Dyer JM, Mullen RT. Arabidopsis thaliana GPAT8 and GPAT9 are localized to the ER and possess distinct ER retrieval signals: functional divergence of the dilysine ER retrieval motif in plant cells. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2009; 47:867-79. [PMID: 19539490 DOI: 10.1016/j.plaphy.2009.05.008] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Revised: 05/14/2009] [Accepted: 05/27/2009] [Indexed: 05/03/2023]
Abstract
Glycerol-3-phosphate acyltransferase (GPAT; EC 2.3.1.15) catalyzes the committed step in the production of glycerolipids, which are major components of cellular membranes, seed storage oils, and epicuticular wax coatings. While the biochemical activities of GPATs have been characterized in detail, the cellular features of these enzymes are only beginning to emerge. Here we characterized the phylogenetic relationships and cellular properties of two GPAT enzymes from the relatively large Arabidopsis thaliana GPAT family, including GPAT8, which is involved in cutin biosynthesis, and GPAT9, which is a new putative GPAT that has extensive homology with a GPAT from mammalian cells involved in storage oil formation and, thus, may have a similar role in plants. Immunofluorescence microscopy of transiently-expressed myc-epitope-tagged GPAT8 and GPAT9 revealed that both proteins were localized to the endoplasmic reticulum (ER), and differential permeabilization experiments indicated that their N- and C-termini were oriented towards the cytosol. However, these two proteins contained distinct types of ER retrieval signals, with GPAT8 possessing a divergent type of dilysine motif (-KK-COOH rather than the prototypic -KKXX-COOH or -KXKXX-COOH motif) and GPAT9 possessing a hydrophobic pentapeptide motif (-phi-X-X-K/R/D/E-phi-; where phi are large hydrophobic amino acid residues). Notably, the divergent dilysine motif in GPAT8 only functioned effectively when additional upstream residues were included to provide the proper protein context. Extensive mutational analyses of the divergent dilysine motif, based upon sequences present in the C-termini of other GPAT8s from various plant species, further expanded the functional definition of this molecular targeting signal, thereby providing insight to the targeting signals in other GPAT family members as well as other ER-resident membrane proteins within plant cells.
Collapse
Affiliation(s)
- Satinder K Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | | | | | | | | |
Collapse
|
18
|
Doolittle MH, Neher SB, Ben-Zeev O, Ling-Liao J, Gallagher CM, Hosseini M, Yin F, Wong H, Walter P, Péterfy M. Lipase maturation factor LMF1, membrane topology and interaction with lipase proteins in the endoplasmic reticulum. J Biol Chem 2009; 284:33623-33. [PMID: 19783858 DOI: 10.1074/jbc.m109.049395] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipase maturation factor 1 (LMF1) is predicted to be a polytopic protein localized to the endoplasmic reticulum (ER) membrane. It functions in the post-translational attainment of enzyme activity for both lipoprotein lipase and hepatic lipase. By using transmembrane prediction methods in mouse and human orthologs, models of LMF1 topology were constructed and tested experimentally. Employing a tagging strategy that used insertion of ectopic glycan attachment sites and terminal fusions of green fluorescent protein, we established a five-transmembrane model, thus dividing LMF1 into six domains. Three domains were found to face the cytoplasm (the amino-terminal domain and loops B and D), and the other half was oriented to the ER lumen (loops A and C and the carboxyl-terminal domain). This representative model shows the arrangement of an evolutionarily conserved domain within LMF1 (DUF1222) that is essential to lipase maturation. DUF1222 comprises four of the six domains, with the two largest ones facing the ER lumen. We showed for the first time, using several naturally occurring variants featuring DUF1222 truncations, that Lmf1 interacts physically with lipoprotein lipase and hepatic lipase and localizes the lipase interaction site to loop C within DUF1222. We discuss the implication of our results with regard to lipase maturation and DUF1222 domain structure.
Collapse
Affiliation(s)
- Mark H Doolittle
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Wendel AA, Lewin TM, Coleman RA. Glycerol-3-phosphate acyltransferases: rate limiting enzymes of triacylglycerol biosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA 2009; 1791:501-6. [PMID: 19038363 PMCID: PMC2737689 DOI: 10.1016/j.bbalip.2008.10.010] [Citation(s) in RCA: 191] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 10/08/2008] [Accepted: 10/28/2008] [Indexed: 12/24/2022]
Abstract
Four homologous isoforms of glycerol-3-phosphate acyltransferase (GPAT), each the product of a separate gene, catalyze the synthesis of lysophosphatidic acid from glycerol-3-phosphate and long-chain acyl-CoA. This step initiates the synthesis of all the glycerolipids and evidence from gain-of-function and loss-of-function studies in mice and in cell culture strongly suggests that each isoform contributes to the synthesis of triacylglycerol. Much work remains to fully delineate the regulation of each GPAT isoform and its individual role in triacylglycerol synthesis.
Collapse
Affiliation(s)
- Angela A Wendel
- Department of Nutrition, CB# 7461, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | | | | |
Collapse
|
20
|
Distler AM, Kerner J, Hoppel CL. Proteomics of mitochondrial inner and outer membranes. Proteomics 2009; 8:4066-82. [PMID: 18763707 DOI: 10.1002/pmic.200800102] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
For the proteomic study of mitochondrial membranes, documented high quality mitochondrial preparations are a necessity to ensure proper localization. Despite the state-of-the-art technologies currently in use, there is no single technique that can be used for all studies of mitochondrial membrane proteins. Herein, we use examples to highlight solubilization techniques, different chromatographic methods, and developments in gel electrophoresis for proteomic analysis of mitochondrial membrane proteins. Blue-native gel electrophoresis has been successful not only for dissection of the inner membrane oxidative phosphorylation system, but also for the components of the outer membrane such as those involved in protein import. Identification of PTMs such as phosphorylation, acetylation, and nitration of mitochondrial membrane proteins has been greatly improved by the use of affinity techniques. However, understanding of the biological effect of these modifications is an area for further exploration. The rapid development of proteomic methods for both identification and quantitation, especially for modifications, will greatly impact the understanding of the mitochondrial membrane proteome.
Collapse
Affiliation(s)
- Anne M Distler
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
| | | | | |
Collapse
|
21
|
Rodríguez-Calvo R, Barroso E, Serrano L, Coll T, Sánchez RM, Merlos M, Palomer X, Laguna JC, Vázquez-Carrera M. Atorvastatin prevents carbohydrate response element binding protein activation in the fructose-fed rat by activating protein kinase A. Hepatology 2009; 49:106-15. [PMID: 19053045 DOI: 10.1002/hep.22570] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
UNLABELLED High fructose intake contributes to the overall epidemic of obesity and metabolic disease. Here we examined whether atorvastatin treatment blocks the activation of the carbohydrate response element binding protein (ChREBP) in the fructose-fed rat. Fructose feeding increased blood pressure (21%, P < 0.05), plasma free fatty acids (59%, P < 0.01), and plasma triglyceride levels (129%, P < 0.001) compared with control rats fed standard chow. These increases were prevented by atorvastatin. Rats fed the fructose-rich diet showed enhanced hepatic messenger RNA (mRNA) levels of glycerol-3-phosphate acyltransferase (Gpat1) (1.45-fold induction, P < 0.05), which is the rate-limiting enzyme for the synthesis of triglycerides, and liver triglyceride content (2.35-fold induction, P < 0.001). Drug treatment inhibited the induction of Gpat1 and increased the expression of liver-type carnitine palmitoyltransferase 1 (L-Cpt-1) (128%, P < 0.01). These observations indicate that atorvastatin diverts fatty acids from triglyceride synthesis to fatty acid oxidation, which is consistent with the reduction in liver triglyceride levels (28%, P < 0.01) observed after atorvastatin treatment. The expression of Gpat1 is regulated by ChREBP and sterol regulatory element binding protein-1c (SREBP-1c). Atorvastatin treatment prevented fructose-induced ChREBP translocation and the increase in ChREBP DNA-binding activity while reducing SREBP-1c DNA-binding activity. Statin treatment increased phospho-protein kinase A (PKA), which promotes nuclear exclusion of ChREBP and reduces its DNA-binding activity. Human HepG2 cells exposed to fructose showed enhanced ChREBP DNA-binding activity, which was not observed in the presence of atorvastatin. Furthermore, atorvastatin treatment increased the CPT-I mRNA levels in these cells. Interestingly, both effects of this drug were abolished in the presence of the PKA inhibitor H89. CONCLUSION These findings indicate that atorvastatin inhibits fructose-induced ChREBP activity and increases CPT-I expression by activating PKA.
Collapse
Affiliation(s)
- Ricardo Rodríguez-Calvo
- Pharmacology Unit, Department of Pharmacology and Therapeutic Chemistry, Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM)-Instituto de Salud Carlos III, University of Barcelona, Spain
| | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Lysophosphatidylcholine acyltransferase 1 (LPCAT1) overexpression in human colorectal cancer. J Mol Med (Berl) 2008; 87:85-97. [PMID: 18974965 DOI: 10.1007/s00109-008-0409-0] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 09/16/2008] [Accepted: 09/25/2008] [Indexed: 01/28/2023]
Abstract
The alteration of the choline metabolite profile is a well-established characteristic of cancer cells. In colorectal cancer (CRC), phosphatidylcholine is the most prominent phospholipid. In the present study, we report that lysophosphatidylcholine acyltransferase 1 (LPCAT1; NM_024830.3), the enzyme that converts lysophosphatidylcholine into phosphatidylcholine, was highly overexpressed in colorectal adenocarcinomas when compared to normal mucosas. Our microarray transcription profiling study showed a significant (p < 10(-8)) transcript overexpression in 168 colorectal adenocarcinomas when compared to ten normal mucosas. Immunohistochemical analysis of colon tumors with a polyclonal antibody to LPCAT1 confirmed the upregulation of the LPCAT1 protein. Overexpression of LPCAT1 in COS7 cells localized the protein to the endoplasmic reticulum and the mitochondria and increased LPCAT1 specific activity 38-fold. In cultured cells, overexpressed LPCAT1 enhanced the incorporation of [(14)C]palmitate into phosphatidylcholine. COS7 cells transfected with LPCAT1 showed no growth rate alteration, in contrast to the colon cancer cell line SW480, which significantly (p < 10(-5)) increased its growth rate by 17%. We conclude that LPCAT1 may contribute to total choline metabolite accumulation via phosphatidylcholine remodeling, thereby altering the CRC lipid profile, a characteristic of malignancy.
Collapse
|
23
|
Abstract
Mutations in PTEN-induced putative kinase 1 (PINK1) are a cause of autosomal recessive familial Parkinson's disease (PD). Efforts in deducing the PINK1 signaling pathway have been hindered by controversy around its subcellular and submitochondrial localization and the authenticity of its reported substrates. We show here that this mitochondrial protein exhibits a topology in which the kinase domain faces the cytoplasm and the N-terminal tail is inside the mitochondria. Although deletion of the transmembrane domain disrupts this topology, common PD-linked PINK1 mutations do not. These results are critical in rectifying the location and orientation of PINK1 in mitochondria, and they should help decipher its normal physiological function and potential pathogenic role in PD.
Collapse
|
24
|
Gimeno RE, Cao J. Thematic review series: glycerolipids. Mammalian glycerol-3-phosphate acyltransferases: new genes for an old activity. J Lipid Res 2008; 49:2079-88. [PMID: 18658143 DOI: 10.1194/jlr.r800013-jlr200] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Glycerol-3-phosphate acyltransferases (GPATs; EC2.3.1.15) catalyze the first step in the de novo synthesis of neutral lipids (triglycerides) and glycerophospholipids. The existence of multiple enzyme isoforms with GPAT activity was predicted many years ago when GPAT activities with distinct kinetic profiles and sensitivity to inhibitors were characterized in two subcellular compartments, mitochondria and microsomes. We now know that mammals have at least four GPAT isoforms with distinct tissue distribution and function. GPAT1 is the major mitochondrial GPAT isoform and is characterized by its resistance to sulfhydryl-modifying reagents, such as N-ethylmaleimide (NEM). GPAT2 is a minor NEM-sensitive mitochondrial isoform. The activity referred to as microsomal GPAT is encoded by two closely related genes, GPAT3 and GPAT4. GPAT isoforms are important regulators of cellular triglyceride and phospholipid content, and may channel fatty acids toward particular metabolic fates. Overexpression and knock-out studies suggest that GPAT isoforms can play important roles in the development of hepatic steatosis, insulin resistance, and obesity; GPAT isoforms are also important for lactation. This review summarizes the current state of knowledge on mammalian GPAT isoforms.
Collapse
Affiliation(s)
- Ruth E Gimeno
- Cardiovascular and Metabolic Diseases, Wyeth Research, Cambridge, MA 02140, USA.
| | | |
Collapse
|
25
|
Zhang YM, Rock CO. Thematic review series: Glycerolipids. Acyltransferases in bacterial glycerophospholipid synthesis. J Lipid Res 2008; 49:1867-74. [PMID: 18369234 DOI: 10.1194/jlr.r800005-jlr200] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Phospholipid biosynthesis is a vital facet of bacterial physiology that begins with the synthesis of the fatty acids by a soluble type II fatty acid synthase. The bacterial glycerol-phosphate acyltransferases utilize the completed fatty acid chains to form the first membrane phospholipid and thus play a critical role in the regulation of membrane biogenesis. The first bacterial acyltransferase described was PlsB, a glycerol-phosphate acyltransferase. PlsB is a key regulatory point that coordinates membrane phospholipid formation with cell growth and macromolecular synthesis. Phosphatidic acid is then produced by PlsC, a 1-acylglycerol-phosphate acyltransferase. These two acyltransferases use thioesters of either CoA or acyl carrier protein (ACP) as the acyl donors and have homologs that perform the same reactions in higher organisms. However, the most prevalent glycerol-phosphate acyltransferase in the bacterial world is PlsY, which uses a recently discovered acyl-phosphate fatty acid intermediate as an acyl donor. This unique activated fatty acid is formed from the acyl-ACP end products of the fatty acid biosynthetic pathway by PlsX, an acyl-ACP:phosphate transacylase.
Collapse
Affiliation(s)
- Yong-Mei Zhang
- Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
| | | |
Collapse
|
26
|
Chen YQ, Kuo MS, Li S, Bui HH, Peake DA, Sanders PE, Thibodeaux SJ, Chu S, Qian YW, Zhao Y, Bredt DS, Moller DE, Konrad RJ, Beigneux AP, Young SG, Cao G. AGPAT6 is a novel microsomal glycerol-3-phosphate acyltransferase. J Biol Chem 2008; 283:10048-57. [PMID: 18238778 DOI: 10.1074/jbc.m708151200] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
AGPAT6 is a member of the 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) family that appears to be important in triglyceride biosynthesis in several tissues, but the precise biochemical function of the enzyme is unknown. In the current study, we show that AGPAT6 is a microsomal glycerol-3-phosphate acyltransferase (GPAT). Membranes from HEK293 cells overexpressing human AGPAT6 had higher levels of GPAT activity. Substrate specificity studies suggested that AGPAT6 was active against both saturated and unsaturated long-chain fatty acyl-CoAs. Both glycerol 3-phosphate and fatty acyl-CoA increased the GPAT activity, and the activity was sensitive to N-ethylmaleimide, a sulfhydryl-modifying reagent. Purified AGPAT6 protein possessed GPAT activity but not AGPAT activity. Using [(13)C(7)]oleic acid labeling and mass spectrometry, we found that overexpression of AGPAT6 increased both lysophosphatidic acid and phosphatidic acid levels in cells. In these studies, total triglyceride and phosphatidylcholine levels were not significantly altered, although there were significant changes in the abundance of specific phosphatidylcholine species. Human AGPAT6 is localized to endoplasmic reticulum and is broadly distributed in tissues. Membranes of mammary epithelial cells from Agpat6-deficient mice exhibited markedly reduced GPAT activity compared with membranes from wild-type mice. Reducing AGPAT6 expression in HEK293 cells through small interfering RNA knockdown suggested that AGPAT6 significantly contributed to HEK293 cellular GPAT activity. Our data indicate that AGPAT6 is a microsomal GPAT, and we propose renaming this enzyme GPAT4.
Collapse
Affiliation(s)
- Yan Qun Chen
- Lilly Research Laboratories, Eli Lilly & Company, Indianapolis, IN 46285, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
27
|
Wang S, Lee DP, Gong N, Schwerbrock NMJ, Mashek DG, Gonzalez-Baró MR, Stapleton C, Li LO, Lewin TM, Coleman RA. Cloning and functional characterization of a novel mitochondrial N-ethylmaleimide-sensitive glycerol-3-phosphate acyltransferase (GPAT2). Arch Biochem Biophys 2007; 465:347-58. [PMID: 17689486 PMCID: PMC2133398 DOI: 10.1016/j.abb.2007.06.033] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Revised: 06/07/2007] [Accepted: 06/11/2007] [Indexed: 12/22/2022]
Abstract
Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the initial and rate-limiting step in glycerolipid synthesis. Several mammalian GPAT activities have been recognized, including N-ethylmaleimide (NEM)-sensitive isoforms in microsomes and mitochondria and an NEM-resistant form in mitochondrial outer membrane (GPAT1). We have now cloned a second mitochondrial isoform, GPAT2 from mouse testis. The open-reading frame encodes a protein of 798 amino acids with a calculated mass of 88.8kDa and 27% amino acid identity to GPAT1. Testis mRNA expression was 50-fold higher than in liver or brown adipose tissue, but the specific activity of NEM-sensitive GPAT in testis mitochondria was similar to that in liver. When Cos-7 cells were transiently transfected with GPAT2, NEM-sensitive GPAT activity increased 30%. Confocal microscopy confirmed a mitochondrial location. Incubation of GPAT2-transfected Cos-7 cells with trace (3 microM; 0.25 microCi) [1-(14)C]oleate for 6h increased incorporation of [(14)C]oleate into TAG 84%. In contrast, incorporation into phospholipid species was lower than in control cells. Although a polyclonal antibody raised against full-length GPAT1 detected an approximately 89-kDa band in liver and testis from GPAT1 null mice and both 89- and 80-kDa bands in BAT from the knockout animals, the GPAT2 protein expressed in Cos-7 cells was only 80 kDa. In vitro translation showed a single product of 89 kDa. Unlike GPAT1, GPAT2 mRNA abundance in liver was not altered by fasting or refeeding. GPAT2 is likely to have a specialized function in testis.
Collapse
Affiliation(s)
- Shuli Wang
- Department of Nutrition, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Yamashita A, Nakanishi H, Suzuki H, Kamata R, Tanaka K, Waku K, Sugiura T. Topology of acyltransferase motifs and substrate specificity and accessibility in 1-acyl-sn-glycero-3-phosphate acyltransferase 1. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:1202-15. [PMID: 17707131 DOI: 10.1016/j.bbalip.2007.07.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 06/22/2007] [Accepted: 07/04/2007] [Indexed: 11/20/2022]
Abstract
1-acyl-sn-glycero-3-phosphate (AGP) acyltransferases (AGPAT) are involved in de novo biosynthesis of glycerolipids, such as phospholipids and triacylglycerol. Alignment of amino acid sequences from AGPAT, sn-glycerol-3-phosphate acyltransferase, and dihydroxyacetonephosphate acyltransferase reveals four regions with strong homology (acyltransferase motifs I-IV). The invariant amino acids within these regions may be part of a catalytically important site in this group of acyl-CoA acyltransferases. However, in human AGPAT1 a transmembrane domain is predicted to separate motif I on the cytosolic side from motifs II-III on the lumenal side, with motif IV near surface of the membrane. The topology of motifs I and III was confirmed by experiments with recombinant AGPAT1 containing potential glycosylation site near the motifs. This topology conflicts with the expectation that catalytically important sites are near one another, raising questions of whether the acyltransferase motifs really are important for AGPAT catalysis, and how substrates access motifs II-III on the lumenal side of the endoplasmic reticulum membrane. Using human AGPAT1 as a model, we have examined the catalytic roles of highly conserved residues in the four acyltransferase motifs by site-directed mutagenesis. Modifications of the sidechain structures of His104, Asp109, Phe146, Arg149, Glu178, Gly179, Thr180, Arg181 and Ile208 all affected AGPAT1 activity, indicating that the acyltransferase motifs indeed are important for AGPAT catalysis. In addition, we examined substrate accessibility to the catalytic domain of human AGPAT1 using a competition assay. Lysophosphatidic acid (LPA) with fatty acid chains shorter than 10 carbons did not access the catalytic domain, suggesting that LPA hydrophobicity is important. In contrast, short chain acyl-CoAs did access the catalytic domain but did not serve as the second substrate. These results suggest that motifs II and III are involved in LPA binding and motifs I and IV are involved in acyl-CoA binding.
Collapse
Affiliation(s)
- Atsushi Yamashita
- Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Sagamihara, Kanagawa 229-0195, Japan.
| | | | | | | | | | | | | |
Collapse
|
29
|
Pellon-Maison M, Montanaro MA, Coleman RA, Gonzalez-Baró MR. Mitochondrial glycerol-3-P acyltransferase 1 is most active in outer mitochondrial membrane but not in mitochondrial associated vesicles (MAV). Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:830-8. [PMID: 17493869 PMCID: PMC2230616 DOI: 10.1016/j.bbalip.2007.04.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2006] [Revised: 03/29/2007] [Accepted: 04/02/2007] [Indexed: 11/18/2022]
Abstract
Glycerol 3-phosphate acyltransferase-1 (GPAT1), catalyzes the committed step in phospholipid and triacylglycerol synthesis. Because both GPAT1 and carnitine-palmitoyltransferase 1 are located on the outer mitochondrial membrane (OMM) it has been suggested that their reciprocal regulation controls acyl-CoA metabolism at the OMM. To determine whether GPAT1, like carnitine-palmitoyltransferase 1, is enriched in both mitochondrial contact sites and OMM, and to correlate protein location and enzymatic function, we used Percoll and sucrose gradient fractionation of rat liver to obtain submitochondrial fractions. Most GPAT1 protein was present in a vesicular membrane fraction associated with mitochondria (MAV) but GPAT specific activity in this fraction was low. In contrast, highest GPAT1 specific activity was present in purified mitochondria. Contact sites from crude mitochondria, which contained markers for both endoplasmic reticulum (ER) and mitochondria, also showed high expression of GPAT1 protein but low specific activity, whereas contact sites isolated from purified mitochondria lacked ER markers and expressed highly active GPAT1. To determine how GPAT1 is targeted to mitochondria, recombinant protein was synthesized in vitro and its incorporation into crude and purified mitochondria was assayed. GPAT1 was rapidly incorporated into mitochondria, but not into microsomes. Incorporation was ATP-driven, and lack of GPAT1 removal by alkali and a chaotropic agent showed that GPAT1 had become an integral membrane protein after incorporation. These results demonstrate that two pools of GPAT1 are present in rat liver mitochondria: an active one, located in OMM and a less active one, located in membranes (ER-contact sites and mitochondrial associated vesicles) associated with both mitochondria and ER.
Collapse
Affiliation(s)
- Magalí Pellon-Maison
- Instituto de Investigaciones Bioquímicas de La Plata (CONICET-UNLP), 60 and 120, 1900 La Plata, Argentina
| | | | | | | |
Collapse
|
30
|
Steinberg GR, Macaulay SL, Febbraio MA, Kemp BE. AMP-activated protein kinase--the fat controller of the energy railroad. Can J Physiol Pharmacol 2007; 84:655-65. [PMID: 16998529 DOI: 10.1139/y06-005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
AMP-activated protein kinase plays an important role in the regulation of lipid metabolism in response to metabolic stress and energy demand. It is also under endocrine control. AMPK acts at multiple steps and has a central role controlling fatty acid, triglyceride, and cholesterol synthesis, as well as the oxidation of fatty acids through direct phosphorylation effects and the control of gene transcription. As such, it can be considered to be the fat controller of the energy railroad. It is thought that AMPK may be a major mediator of the health benefits of exercise in mitigating the development of obesity and age-onset diseases.
Collapse
|
31
|
Lu YJ, Zhang F, Grimes KD, Lee RE, Rock CO. Topology and active site of PlsY: the bacterial acylphosphate:glycerol-3-phosphate acyltransferase. J Biol Chem 2007; 282:11339-46. [PMID: 17308305 DOI: 10.1074/jbc.m700374200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The most widely distributed biosynthetic pathway to initiate phosphatidic acid formation in bacterial membrane phospholipid biosynthesis involves the conversion of acyl-acyl carrier protein to acylphosphate by PlsX and the transfer of the acyl group from acylphosphate to glycerol 3-phosphate by an integral membrane protein, PlsY. The membrane topology of Streptococcus pneumoniae PlsY was determined using the substituted cysteine accessibility method. PlsY has five membrane-spanning segments with the amino terminus and two short loops located on the external face of the membrane. Each of the three larger cytoplasmic domains contains a highly conserved sequence motif. Site-directed mutagenesis revealed that each conserved domain was critical for PlsY catalysis. Motif 1 had an essential serine and arginine residue. Motif 2 had the characteristics of a phosphate-binding loop. Mutations of the conserved glycines in motif 2 to alanines resulted in a Km defect for glycerol 3-phosphate binding leading to the conclusion that this motif corresponded to the glycerol 3-phosphate binding site. Motif 3 contained a conserved histidine and asparagine that were important for activity and a glutamate that was critical to the structural integrity of PlsY. PlsY was noncompetitively inhibited by palmitoyl-CoA. These data define the membrane architecture and the critical active site residues in the PlsY family of bacterial acyltransferases.
Collapse
Affiliation(s)
- Ying-Jie Lu
- Department of Infectious Diseases, St. Jude Children's Research Hospital, and Department of Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee 38105-2794, USA
| | | | | | | | | |
Collapse
|
32
|
Harada N, Hara S, Yoshida M, Zenitani T, Mawatari K, Nakano M, Takahashi A, Hosaka T, Yoshimoto K, Nakaya Y. Molecular cloning of a murine glycerol-3-phosphate acyltransferase-like protein 1 (xGPAT1). Mol Cell Biochem 2006; 297:41-51. [PMID: 17013544 DOI: 10.1007/s11010-006-9321-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2006] [Accepted: 08/25/2006] [Indexed: 10/24/2022]
Abstract
A novel murine glycerol-3-phosphate acyltransferase-like protein 1 (named xGPAT1) has been cloned. The mouse xGPAT1 gene is located on mouse Chromosome 2, spans >19 kb, and consists of at least 23 exons. The protein is 32% identical and 72% similar to mouse mitochondrial GPAT (mtGPAT) on the amino acid level. Sequencing analysis confirmed that xGPAT1 has a 2403-bp open reading frame (ORF) that encodes an 801-amino acid protein with an estimated molecular mass of 89.1 kDa. A hydropathy plot of the deduced xGPAT1 protein showed a high degree of similarity with that of the mtGPAT protein. Using 5'-rapid amplification of cDNA ends, two alternate, untranslated exon 1 (1a and b) isoforms were obtained, generating variants xGPAT1-v1 and xGPAT1-v2. xGPAT1-v1 is expressed in mouse heart, liver, spleen, kidney and murine inner medullary collecting duct 3 (mIMCD3) cells, while xGPAT1-v2 is expressed in mouse liver, spleen, kidney, white and brown adipose tissues and 3T3-L1 pre- and post-adipocytes. xGPAT1 was distributed in the membrane fraction and showed GPAT activity when epitope-tagged xGPAT1 was expressed in Chinese hamster ovary (CHO)-K1 cells.
Collapse
Affiliation(s)
- Nagakatsu Harada
- Department of Nutrition and Metabolism, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15, Kuramoto-cho, Tokushima City 770-8503, Japan.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Xu H, Wilcox D, Nguyen P, Voorbach M, Suhar T, Morgan SJ, An WF, Ge L, Green J, Wu Z, Gimeno RE, Reilly R, Jacobson PB, Collins CA, Landschulz K, Surowy T. Hepatic knockdown of mitochondrial GPAT1 in ob/ob mice improves metabolic profile. Biochem Biophys Res Commun 2006; 349:439-48. [PMID: 16935266 DOI: 10.1016/j.bbrc.2006.08.071] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Accepted: 08/15/2006] [Indexed: 10/24/2022]
Abstract
Glycerol-3-phosphate acyltransferase (GPAT) controls the first step of triglyceride (TAG) synthesis. Three distinct GPAT activities have been identified, two localized in mitochondria and one in microsomes. Mitochondrial GPAT1 (mtGPAT1) is abundantly expressed in the liver and constitutes approximately 50% of total GPAT activities in this organ. Hepatic mtGPAT1 activity is elevated in obese rodents. Mice deficient in mtGPAT1 have an improved lipid profile. To investigate if beneficial effects can result from reduced hepatic expression of mtGPAT1 in adult obese mice, adenoviral vector-based short hairpin RNA interference (shRNA) technology was used to knockdown mtGPAT1 expression in livers of ob/ob mice. Reduced expression of mtGPAT1 mRNA in liver of ob/ob mice resulted in dramatic and dose dependent reduction in mtGPAT1 activity. Reduced hepatic TAG, diacylglycerol, and free fatty acid, as well as reduced plasma cholesterol and glucose, were also observed. Fatty acid composition analysis revealed decrease of C16:0 in major lipid species. Our results demonstrate that acute reduction of mtGPAT1 in liver of ob/ob mice reduces TAG synthesis, which points to a role for mtGPAT1 in the correction of obesity and related disorders.
Collapse
Affiliation(s)
- Haiyan Xu
- Metabolic Disease Research, Abbott Laboratories, Abbott Park, IL 60064, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Burri L, Vascotto K, Gentle IE, Chan NC, Beilharz T, Stapleton DI, Ramage L, Lithgow T. Integral membrane proteins in the mitochondrial outer membrane of Saccharomyces cerevisiae. FEBS J 2006; 273:1507-15. [PMID: 16689936 DOI: 10.1111/j.1742-4658.2006.05171.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Mitochondria evolved from a bacterial endosymbiont ancestor in which the integral outer membrane proteins would have been beta-barrel structured within the plane of the membrane. Initial proteomics on the outer membrane from yeast mitochondria suggest that while most of the protein components are integral in the membrane, most of these mitochondrial proteins behave as if they have alpha-helical transmembrane domains, rather than beta-barrels. These proteins are usually predicted to have a single alpha-helical transmembrane segment at either the N- or C-terminus, however, more complex topologies are also seen. We purified the novel outer membrane protein Om14 and show it is encoded in the gene YBR230c. Protein sequencing revealed an intron is spliced from the transcript, and both transcription from the YBR230c gene and steady-state level of the Om14 protein is dramatically less in cells grown on glucose than in cells grown on nonfermentable carbon sources. Hydropathy predictions together with data from limited protease digestion show three alpha-helical transmembrane segments in Om14. The alpha-helical outer membrane proteins provide functions derived after the endosymbiotic event, and require the translocase in the outer mitochondrial membrane complex for insertion into the outer membrane.
Collapse
Affiliation(s)
- Lena Burri
- Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Australia
| | | | | | | | | | | | | | | |
Collapse
|
35
|
Pellon-Maison M, Coleman RA, Gonzalez-Baró MR. The C-terminal region of mitochondrial glycerol-3-phosphate acyltransferase-1 interacts with the active site region and is required for activity. Arch Biochem Biophys 2006; 450:157-66. [PMID: 16620760 DOI: 10.1016/j.abb.2006.03.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 03/08/2006] [Accepted: 03/08/2006] [Indexed: 11/19/2022]
Abstract
Glycerol phosphate acyltransferase (GPAT) catalyzes the formation of 1-acyl-sn-glycerol-3-phosphate from glycerol-3-phosphate and long chain fatty acyl-CoA substrates. We previously determined the topography of the mitochondrial GPAT1 isoform (mtGPAT1, 828 amino acids). mtGPAT1 has two transmembrane domains (TMDs) (aa 472-493 and aa 576-592) with both the N- and C-termini facing the cytosol and a loop (aa 494-575) facing the intermembrane space. Alignment of amino acid sequences from mtGPAT1 and other acyltransferases and site directed mutagenesis studies have demonstrated that the active site of the enzyme resides in the N-terminal domain of the protein. In this study, we sequentially truncated the C-terminal domain and characterized the properties of the resulting mutants expressed in CHO cells. Although the mutants were overexpressed, none of them conferred GPAT activity. The loss of activity was not due to the miss-targeting of the proteins since immunofluorescence experiments demonstrated their mitochondrial localization. Instead, chemical crosslinking and protein cleavage studies demonstrated that the N- and C-termini of the protein interact. These results suggest that the C-terminal domain is necessary for mtGPAT1 activity, and probably contributes to catalysis or substrate binding.
Collapse
|
36
|
Lindén D, William-Olsson L, Ahnmark A, Ekroos K, Hallberg C, Sjögren HP, Becker B, Svensson L, Clapham JC, Oscarsson J, Schreyer S. Liver-directed overexpression of mitochondrial glycerol-3-phosphate acyltransferase results in hepatic steatosis, increased triacylglycerol secretion and reduced fatty acid oxidation. FASEB J 2006; 20:434-43. [PMID: 16507761 DOI: 10.1096/fj.05-4568com] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first committed step in triacylglycerol (TAG) and phospholipid biosynthesis. GPAT activity has been identified in both ER and mitochondrial subcellular fractions. The ER activity dominates in most tissues except in liver, where the mitochondrial isoform (mtGPAT) can constitute up to 50% of the total activity. To study the in vivo effects of hepatic mtGPAT overexpression, mice were transduced with adenoviruses expressing either murine mtGPAT or a catalytically inactive variant of the enzyme. Overexpressing mtGPAT resulted in massive 12- and 7-fold accumulation of liver TAG and diacylglycerol, respectively but had no effect on phospholipid or cholesterol ester content. Histological analysis showed extensive lipid accumulation in hepatocytes. Furthermore, mtGPAT transduction markedly increased adipocyte differentiation-related protein and stearoyl-CoA desaturase-1 (SCD-1) in the liver. In line with increased SCD-1 expression, 18:1 and 16:1 in the hepatic TAG fraction increased. In addition, mtGPAT overexpression decreased ex vivo fatty acid oxidation, increased liver TAG secretion rate 2-fold, and increased plasma TAG and cholesterol levels. These results support the hypothesis that increased hepatic mtGPAT activity associated with obesity and insulin resistance contributes to increased TAG biosynthesis and inhibition of fatty acid oxidation, responses that would promote hepatic steatosis and dyslipidemia.
Collapse
Affiliation(s)
- Daniel Lindén
- Department of Integrative Pharmacology, AstraZeneca R&D, S-431 83 Mölndal, Sweden.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
37
|
Gully D, Bouveret E. A protein network for phospholipid synthesis uncovered by a variant of the tandem affinity purification method in Escherichia coli. Proteomics 2006; 6:282-93. [PMID: 16294310 DOI: 10.1002/pmic.200500115] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In prokaryotes, acyl carrier protein (ACP) is a cofactor central to a myriad of syntheses, including fatty acid and phospholipid synthesis. To fulfill its function, ACP must therefore interact with a multitude of different enzymes, which includes the thioesterase YbgC. We found a specific interaction between ACP and YbgC whose thioesterase activity has been demonstrated in vitro on acyl-CoA derivatives, but whose physiological function in bacteria remains unknown. Therefore, YbgC could be a thioesterase active on some specific acyl-ACPs. We then assigned a function to the ACP/YbgC pair by employing a proteomic approach derived from tandem affinity purification, the split tag method. This technique allowed us to purify proteins interacting with ACP and YbgC proteins at the same time. Interactions with PlsB, a sn-glycerol-3-phosphate acyltransferase and PssA, a phosphatidylserine synthase, were identified and validated, showing that YbgC is involved in phospholipid metabolism. Furthermore, using an in vivo bacterial two-hybrid interaction analysis, we showed for the first time that enzymes of the phospholipid synthesis pathway form a complex in the inner membrane. Taken together, these results describe an integrated protein network that could be involved in the coordination of phospholipid metabolism.
Collapse
Affiliation(s)
- Djamel Gully
- LISM, IBSM, CNRS, 31 chemin Joseph Aiguier, 13402 Marseille, France
| | | |
Collapse
|
38
|
Roy R, Ordovas L, Taourit S, Zaragoza P, Eggen A, Rodellar C. Genomic structure and an alternative transcript of bovine mitochondrial glycerol-3-phosphate acyltransferase gene (GPAM). Cytogenet Genome Res 2006; 112:82-9. [PMID: 16276094 DOI: 10.1159/000087517] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2005] [Accepted: 05/18/2005] [Indexed: 11/19/2022] Open
Abstract
GPAM maps in BTA26q22, where several QTLs affecting milk production, milk fat and protein content have been mapped. On the basis of the QTL location, the GPAM gene could be considered a good candidate gene for the mentioned traits. Glycerol-3-phosphate acyltransferase mitochondrial (GPAM) is the enzyme that catalyses the initial and committed step of glycerolipid synthesis and, therefore, it is a potential site for triacylglycerol synthesis regulation. In this study, the structure of the cDNA and the genomic DNA of the bovine GPAM gene were determined and the expression of its mRNA was studied. The cDNA of the gene was cloned by RT-PCR, 5' and 3' rapid amplification of cDNA ends. The GPAM mRNA sequence contains a 2,475-bp coding region and a 3,689-bp 3' UTR. Its ORF encoded for an 825-amino acid protein and has an 89% homology with the coding regions of previously characterized mouse and human GPAM genes. The predicted amino acid sequence had an 89 and 93% similarity with mouse and human GPAM proteins, respectively. Using a 5' RACE strategy, two different 5' UTRs were cloned. Northern blot analysis confirmed the presence of two different transcripts. Adipose tissues and lung had the highest levels of GPAM mRNA expression, whereas it was barely detectable in liver. This expression pattern differs with those of non-ruminant animals where liver is one of the tissues with higher GPAM mRNA expression level.
Collapse
Affiliation(s)
- R Roy
- Laboratorio de Genética Bioquímica, Universidad de Zaragoza, Zaragoza, Spain.
| | | | | | | | | | | |
Collapse
|
39
|
Kusunoki J, Kanatani A, Moller DE. Modulation of fatty acid metabolism as a potential approach to the treatment of obesity and the metabolic syndrome. Endocrine 2006; 29:91-100. [PMID: 16622296 DOI: 10.1385/endo:29:1:91] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Revised: 11/30/1999] [Accepted: 10/20/2005] [Indexed: 12/21/2022]
Abstract
Increased de novo lipogenesis and reduced fatty acid oxidation are probable contributors to adipose accretion in obesity. Moreover, these perturbations have a role in leading to non-alcoholic steatohepatitis, dyslipidemia, and insulin resistance--via "lipotoxicity"-related mechanisms. Research in this area has prompted an effort to evaluate several discrete enzymes in these pathways as targets for future therapeutic intervention. Acetyl-CoA carboxylase 1 (ACC1) and ACC2 regulate fatty acid synthesis and indirectly control fatty acid oxidation via a key product, malonyl CoA. Based on mouse genetic and preclinical pharmacologic evidence, inhibition of ACC1 and/or ACC2 may be a useful approach to treat obesity and metabolic syndrome. Similarly, available data suggest that inhibition of other enzymes in this pathway, including fatty acid synthase, stearoyl CoA desaturase, and diacylglycerol acytransferase 1, will have beneficial effects. AMP-activated protein kinase is a master regulator of nutrient metabolism, which controls several aspects of lipid metabolism. Activation of AMPK in selected tissues is also a potential therapeutic approach. Inhibition of hormone-sensitive lipase is another possible approach. The rationale for modulating the activity of these enzymes and their relative merits (and downsides) as possible therapeutic targets are further discussed.
Collapse
Affiliation(s)
- Jun Kusunoki
- Department of Metabolic Disorders, Banyu-Tsukuba Research Institute, Tsukuba, Japan
| | | | | |
Collapse
|
40
|
Abstract
Stearoyl-CoA desaturase (SCD) is an integral membrane protein anchored in the endoplasmic reticulum. It catalyzes the biosynthesis of monounsaturated fatty acids that are required for the synthesis of triglycerides, cholesteryl esters, and phospholipids. Four mouse isoforms of SCD (SCD1-4) and two human isoforms have been characterized. In the current study, we characterize the topology of the mouse SCD1 isoform. Hydropathy analysis of the 355-amino acid mouse SCD1 protein predicts that the protein contains four transmembrane domains (TMDs) and three loops connecting the membrane-spanning domains. To define the topology of the protein, recombinant SCD1 constructs containing epitope tags were transiently expressed in HeLa cells and analyzed by indirect immunofluorescence and cysteine derivatization. Our data provide evidence that the N and C termini of SCD1 are oriented toward the cytosol with four transmembrane domains separated by two very short hydrophilic loops in the ER lumen and one large hydrophilic loop in the cytosol. In addition, based on the previous observation that SCD is a thiol enzyme, we sought to investigate whether the cysteine residues were essential for enzyme activity through mutagenesis studies, and our data suggest that the cysteines in SCD are not catalytically essential.
Collapse
Affiliation(s)
- Weng Chi Man
- Biochemistry andNutritional Sciences, University of Wisconsin-Madison, 53706, USA
| | | | | | | |
Collapse
|
41
|
Onorato TM, Chakraborty S, Haldar D. Phosphorylation of Rat Liver Mitochondrial Glycerol-3-phosphate Acyltransferase by Casein Kinase 2. J Biol Chem 2005; 280:19527-34. [PMID: 15778226 DOI: 10.1074/jbc.m410422200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously shown rat liver mitochondrial glycerol-3-phosphate acyltransferase (mtGAT), which catalyzes the first step in de novo glycerolipid biosynthesis, is stimulated by casein kinase 2 (CK2) and that a phosphorylated protein of approximately 85 kDa is present in CK2-treated mitochondria. In this paper, we have identified the (32)P-labeled 85-kDa protein as mtGAT. We have also investigated whether the phosphorylation of mtGAT is because of CK2. Mitochondria were treated with CK2 and [gamma-(32)P]GTP as the phosphate donor. Autoradiography, Western blot, and immunoprecipitation results showed mtGAT was phosphorylated by CK2. Next, we incubated mitochondria with CK2 and either ATP or GTP, in the presence of heparin, a known inhibitor of CK2. Heparin inhibited CK2-induced stimulation of mtGAT activity; this inhibition resulted in decreased (32)P-labeling of mtGAT. Additionally, mitochondria were treated with CK2 and [gamma-(32)P]ATP in the presence of staurosporine (a serine/threonine protein kinase inhibitor), genistein (a tyrosine kinase inhibitor), and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB, a CK2 inhibitor). Only DRB, the CK2 inhibitor, greatly reduced the amount of (32)P-incorporation into mtGAT by CK2. Finally, isolated mitochondrial outer membrane was incubated with cytosol in the presence of [gamma-(32)P]GTP; (32)P-labeled mtGAT was detected. Collectively, these data suggest that CK2 phosphorylates mtGAT. The impact of our results in the regulation of mtGAT and other anabolic processes is discussed.
Collapse
Affiliation(s)
- Thomas M Onorato
- Department of Biological Sciences, St. John's University, Queens, New York 11439, USA
| | | | | |
Collapse
|
42
|
Zufferey R, Mamoun CB. The initial step of glycerolipid metabolism inLeishmania majorpromastigotes involves a single glycerol-3-phosphate acyltransferase enzyme important for the synthesis of triacylglycerol but not essential for virulence. Mol Microbiol 2005; 56:800-10. [PMID: 15819633 DOI: 10.1111/j.1365-2958.2005.04579.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The synthesis of the major phospholipids, including those that play an essential role in Leishmania virulence, initiates with the acylation of glycerol-3-phosphate and dihydroxyacetonephosphate at the sn-1 position by glycerol-3-phosphate and dihydroxyacetonephosphate acyltransferases respectively. In this study, we show that Leishmania major promastigotes express a single glycerol-3-phosphate acyltransferase activity important for triacylglycerol synthesis but not essential for virulence. The encoding gene, LmGAT, expressed in yeast results in full complementation of the lethality of a mutant, gat1Deltagat2Delta, lacking glycerol-3-phosphate activity. Biochemical analyses revealed that LmGAT is a low-affinity glycerol-3-phosphate acyltransferase and exhibits higher specific activity with unsaturated long fatty acyl-CoA donors. A L. major null mutant, Deltalmgat/Deltalmgat, was created and a thorough analysis of its lipid composition was performed. Deletion of LmGAT resulted in a complete loss of Leishmania glycerol-3-phosphate acyltransferase activity and a major reduction in triacylglycerol synthesis. Consistent with the specificity of LmGAT for glycerol-3-phosphate but not dihydroxyacetonephosphate, Deltalmgat/Deltalmgat mutant expressed normal levels of the ether-lipid derivatives and virulence factors, lipophosphoglycan and GPI-anchored proteins, gp63, and its virulence was not affected in mice.
Collapse
Affiliation(s)
- Rachel Zufferey
- Center for Microbial Pathogenesis, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030, USA
| | | |
Collapse
|
43
|
Lindén D, William-Olsson L, Rhedin M, Asztély AK, Clapham JC, Schreyer S. Overexpression of mitochondrial GPAT in rat hepatocytes leads to decreased fatty acid oxidation and increased glycerolipid biosynthesis. J Lipid Res 2004; 45:1279-88. [PMID: 15102885 DOI: 10.1194/jlr.m400010-jlr200] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycerol-3-phosphate acyltransferase (GPAT) catalyses the first committed step in glycerolipid biosynthesis. The mitochondrial isoform (mtGPAT) is mainly expressed in liver, where it is highly regulated, indicating that mtGPAT may have a unique role in hepatic fatty acid metabolism. Because both mtGPAT and carnitine palmitoyl transferase-1 are located on the outer mitochondrial membrane, we hypothesized that mtGPAT directs fatty acyl-CoA away from beta-oxidation and toward glycerolipid synthesis. Adenoviral-mediated overexpression of murine mtGPAT in primary cultures of rat hepatocytes increased mtGPAT activity 2.7-fold with no compensatory effect on microsomal GPAT activity. MtGPAT overexpression resulted in a dramatic 80% reduction in fatty acid oxidation and a significant increase in hepatic diacylglycerol and phospholipid biosynthesis. Following lipid loading of the cells, intracellular triacylglycerol biosynthesis was also induced by mtGPAT overexpression. Changing an invariant aspartic acid residue to a glycine [D235G] in mtGPAT resulted in an inactive enzyme, which helps define the active site required for mammalian mtGPAT function. To determine if obesity increases hepatic mtGPAT activity, two models of rodent obesity were examined and shown to have >2-fold increased enzyme activity. Overall, these results support the concept that increased hepatic mtGPAT activity associated with obesity positively contributes to lipid disorders by reducing oxidative processes and promoting de novo glycerolipid synthesis.
Collapse
|
44
|
Orsini F, Migliaccio E, Moroni M, Contursi C, Raker VA, Piccini D, Martin-Padura I, Pelliccia G, Trinei M, Bono M, Puri C, Tacchetti C, Ferrini M, Mannucci R, Nicoletti I, Lanfrancone L, Giorgio M, Pelicci PG. The life span determinant p66Shc localizes to mitochondria where it associates with mitochondrial heat shock protein 70 and regulates trans-membrane potential. J Biol Chem 2004; 279:25689-95. [PMID: 15078873 DOI: 10.1074/jbc.m401844200] [Citation(s) in RCA: 219] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
P66Shc regulates life span in mammals and is a critical component of the apoptotic response to oxidative stress. It functions as a downstream target of the tumor suppressor p53 and is indispensable for the ability of oxidative stress-activated p53 to induce apoptosis. The molecular mechanisms underlying the apoptogenic effect of p66Shc are unknown. Here we report the following three findings. (i) The apoptosome can be properly activated in vitro in the absence of p66Shc only if purified cytochrome c is supplied. (ii) Cytochrome c release after oxidative signals is impaired in the absence of p66Shc. (iii) p66Shc induces the collapse of the mitochondrial trans-membrane potential after oxidative stress. Furthermore, we showed that a fraction of cytosolic p66Shc localizes within mitochondria where it forms a complex with mitochondrial Hsp70. Treatment of cells with ultraviolet radiation induced the dissociation of this complex and the release of monomeric p66Shc. We propose that p66Shc regulates the mitochondrial pathway of apoptosis by inducing mitochondrial damage after dissociation from an inhibitory protein complex. Genetic and biochemical evidence suggests that mitochondria regulate life span through their effects on the energetic metabolism (mitochondrial theory of aging). Our data suggest that mitochondrial regulation of apoptosis might also contribute to life span determination.
Collapse
Affiliation(s)
- Francesca Orsini
- Department of Experimental Oncology, European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Han GS, Johnston CN, Carman GM. Vacuole membrane topography of the DPP1-encoded diacylglycerol pyrophosphate phosphatase catalytic site from Saccharomyces cerevisiae. J Biol Chem 2003; 279:5338-45. [PMID: 14630917 DOI: 10.1074/jbc.m311779200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Saccharomyces cerevisiae DPP1-encoded diacylglycerol pyrophosphate phosphatase is a vacuole membrane-associated enzyme that catalyzes the removal of the beta-phosphate from diacylglycerol pyrophosphate to form phosphatidate, and it then removes the phosphate from phosphatidate to form diacylglycerol. The enzyme has six putative transmembrane domains and a hydrophilic region that contains a phosphatase motif required for its catalytic activity. In this work, we examined the topography of diacylglycerol-pyrophosphate phosphatase catalytic site within the transverse plane of the vacuole membrane. Results of protease protection analysis using endoproteinase Lys-C and labeling of cysteine residues using sulfhydryl reagents were consistent with a model where the catalytic site of diacylglycerol-pyrophosphate phosphatase was oriented to the cytosolic face of the vacuole membrane. In addition, diacylglycerol-pyrophosphate phosphatase activity was found with intact vacuoles. The phospholipids diacylglycerol pyrophosphate (0.6 mol %) and phosphatidate (1.4 mol %) were found in the vacuole membrane, and their levels decreased to an undetectable level and by 79%, respectively, when cells were depleted for zinc. The reduced levels of diacylglycerol pyrophosphate and phosphatidate correlated with the induced expression of diacylglycerol-pyrophosphate phosphatase. This work suggested that diacylglycerol pyrophosphate phosphatase functions to regulate the levels of diacylglycerol pyrophosphate and phosphatidate on the cytosolic face of the vacuole membrane.
Collapse
Affiliation(s)
- Gil-Soo Han
- Department of Food Science, Rutgers University, New Brunswick, New Jersey 08901, USA
| | | | | |
Collapse
|
46
|
Zaremberg V, McMaster CR. Differential partitioning of lipids metabolized by separate yeast glycerol-3-phosphate acyltransferases reveals that phospholipase D generation of phosphatidic acid mediates sensitivity to choline-containing lysolipids and drugs. J Biol Chem 2002; 277:39035-44. [PMID: 12167660 DOI: 10.1074/jbc.m207753200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study we demonstrate that the GAT1 and GAT2 genes encode the major glycerol-3-phosphate acyltransferase activities in Saccharomyces cerevisiae. Genetic inactivation of either GAT1 or GAT2 did not alter cell growth but inactivation of both resulted in growth cessation. Metabolic analyses of gat1 and gat2 yeast detected that the major differences were: (i) a 50% increase in the rate of triacylglycerol synthesis in gat1 yeast and a corresponding 50% decrease in gat2 yeast, and (ii) a 5-fold increase in glycerophosphocholine production through deacylation of phosphatidylcholine synthesized through the CDP-choline pathway in gat1 yeast, whereas gat2 yeast displayed a 10-fold decrease. To address why we observed alterations in phospholipid turnover specific to phosphatidylcholine produced through the CDP-choline pathway in gat1 and gat2 yeast we tested their sensitivity to various cytotoxic lysolipids and observed that gat2 cells were more sensitive to lysophosphatidylcholine, but not other lysolipids. To pursue the mechanism we analyzed their sensitivity to choline-containing lysolipids or drugs that could not be deacylated and/or reacylated. Our data showed that gat1 and gat2 yeast were resistant and sensitive to lysoplatelet activating factor, platelet activating factor, and the anti-tumor lipid edelfosine, respectively, indicating that their sensitivity to these compounds was not because of differences in rates of phosphatidylcholine deacylation. As growth of gat2 cells was impaired in the presence of ethanol, a phospholipase D (Spo14p) inhibitor, we inferred that phospholipase D may play important biologic and metabolic roles in phenotypes observed in gat yeast. Genetic inactivation of the SPO14 gene resulted in increased susceptibility, whereas expression of Escherichia coli diacylglycerol kinase relieved growth inhibition, to choline-containing lysolipids and drugs. Our results are consistent with a model whereby phosphatidic acid generated from phosphatidylcholine hydrolysis by Spo14p regulates susceptibility to choline-containing lysolipid analogs and drugs.
Collapse
Affiliation(s)
- Vanina Zaremberg
- Atlantic Research Centre, Department of Pediatrics, IWK Health Centre, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
| | | |
Collapse
|