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Jennings W, Doshi S, Hota PK, Prodeus A, Black S, Epand RM. Expression, Purification, and Properties of a Human Arachidonoyl-Specific Isoform of Diacylglycerol Kinase. Biochemistry 2017; 56:1337-1347. [PMID: 28199087 DOI: 10.1021/acs.biochem.6b01193] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Diacylglycerol kinase ε (DGKε) catalyzes the phosphorylation of diacylglycerol, producing phosphatidic acid. DGKε demonstrates exquisite specificity for the acyl chains of diacylglycerol. This contributes to the enrichment of particular acyl chains within the lipids of the phosphatidylinositol cycle. Phosphatidylinositol is highly enriched with 1-stearoyl-2-arachidonoyl, which is important for maintaining cellular health. Dysregulation of DGKε perturbs lipid signaling and biosynthesis, which has been linked to epilepsy, Huntington's disease, and heart disease. Recessive loss-of-function mutations in the DGKε gene cause atypical hemolytic uremic syndrome. Because DGKε has never been purified, little is known about its molecular properties. We expressed human DGKε and a truncated version lacking the first 40 residues (DGKεΔ40) and purified both proteins to near homogeneity using nickel affinity chromatography. Kinase activity measurements showed that both purified constructs retained their acyl chain specificity for diacylglycerol with an activity level comparable to that of N-terminally FLAG epitope-tagged forms of these proteins expressed in COS7 cells. Both constructs lost activity upon being stored, particularly upon freezing and thawing, which was minimized by the addition of glycerol. Circular dichroism revealed that DGKε and DGKεΔ40 both contain significant amounts of α-helical and β structure and exhibit biphasic thermal denaturations. The loss of secondary structure upon heating was irreversible for both constructs, with relatively little effect of added dioleoylphosphatidylcholine. The addition of 50% glycerol stabilized both constructs and facilitated refolding of their secondary structures after heating. This is the first successful purification and characterization of DGKε's enzymatic and conformational properties. The purification of DGKε permits detailed analyses of this unique enzyme and will improve our understanding of DGKε-related diseases.
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Affiliation(s)
- William Jennings
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | - Sejal Doshi
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | - Prasanta Kumar Hota
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | - Aaron Prodeus
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | - Stephanie Black
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
| | - Richard M Epand
- Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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Epand RM, So V, Jennings W, Khadka B, Gupta RS, Lemaire M. Diacylglycerol Kinase-ε: Properties and Biological Roles. Front Cell Dev Biol 2016; 4:112. [PMID: 27803897 PMCID: PMC5067486 DOI: 10.3389/fcell.2016.00112] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 09/27/2016] [Indexed: 12/20/2022] Open
Abstract
In mammals there are at least 10 isoforms of diacylglycerol kinases (DGK). All catalyze the phosphorylation of diacylglycerol (DAG) to phosphatidic acid (PA). Among DGK isoforms, DGKε has several unique features. It is the only DGK isoform with specificity for a particular species of DAG, i.e., 1-stearoyl-2-arachidonoyl glycerol. The smallest of all known DGK isoforms, DGKε, is also the only DGK devoid of a regulatory domain. DGKε is the only DGK isoform that has a hydrophobic segment that is predicted to form a transmembrane helix. As the only membrane-bound, constitutively active DGK isoform with exquisite specificity for particular molecular species of DAG, the functional overlap between DGKε and other DGKs is predicted to be minimal. DGKε exhibits specificity for DAG containing the same acyl chains as those found in the lipid intermediates of the phosphatidylinositol-cycle. It has also been shown that DGKε affects the acyl chain composition of phosphatidylinositol in whole cells. It is thus likely that DGKε is responsible for catalyzing one step in the phosphatidylinositol-cycle. Steps of this cycle take place in both the plasma membrane and the endoplasmic reticulum membrane. DGKε is likely present in both of these membranes. DGKε is the only DGK isoform that is associated with a human disease. Indeed, recessive loss-of-function mutations in DGKε cause atypical hemolytic-uremic syndrome (aHUS). This condition is characterized by thrombosis in the small vessels of the kidney. It causes acute renal insufficiency in infancy and most patients develop end-stage renal failure before adulthood. Disease pathophysiology is poorly understood and there is no therapy. There are also data suggesting that DGKε may play a role in epilepsy and Huntington disease. Thus, DGKε has many unique molecular and biochemical properties when compared to all other DGK isoforms. DGKε homologs also contain a number of conserved sequence features that are distinctive characteristics of either the rodents or specific groups of primate homologs. How cells, tissues and organisms harness DGKε's catalytic prowess remains unclear. The discovery of DGKε's role in causing aHUS will hopefully boost efforts to unravel the mechanisms by which DGKε dysfunction causes disease.
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Affiliation(s)
- Richard M Epand
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Vincent So
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences CentreHamilton, ON, Canada; Nephrology Division and Cell Biology Program, Hospital for Sick ChildrenToronto, ON, Canada
| | - William Jennings
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Bijendra Khadka
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Radhey S Gupta
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Mathieu Lemaire
- Nephrology Division and Cell Biology Program, Hospital for Sick ChildrenToronto, ON, Canada; Department of Biochemistry, University of TorontoToronto, ON, Canada; Institute of Medicine, University of TorontoToronto, ON, Canada
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Epand RM, So V, Jennings W, Khadka B, Gupta RS, Lemaire M. Diacylglycerol Kinase-ε: Properties and Biological Roles. Front Cell Dev Biol 2016. [PMID: 27803897 DOI: 10.3389/fcell.2016.00112)] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
In mammals there are at least 10 isoforms of diacylglycerol kinases (DGK). All catalyze the phosphorylation of diacylglycerol (DAG) to phosphatidic acid (PA). Among DGK isoforms, DGKε has several unique features. It is the only DGK isoform with specificity for a particular species of DAG, i.e., 1-stearoyl-2-arachidonoyl glycerol. The smallest of all known DGK isoforms, DGKε, is also the only DGK devoid of a regulatory domain. DGKε is the only DGK isoform that has a hydrophobic segment that is predicted to form a transmembrane helix. As the only membrane-bound, constitutively active DGK isoform with exquisite specificity for particular molecular species of DAG, the functional overlap between DGKε and other DGKs is predicted to be minimal. DGKε exhibits specificity for DAG containing the same acyl chains as those found in the lipid intermediates of the phosphatidylinositol-cycle. It has also been shown that DGKε affects the acyl chain composition of phosphatidylinositol in whole cells. It is thus likely that DGKε is responsible for catalyzing one step in the phosphatidylinositol-cycle. Steps of this cycle take place in both the plasma membrane and the endoplasmic reticulum membrane. DGKε is likely present in both of these membranes. DGKε is the only DGK isoform that is associated with a human disease. Indeed, recessive loss-of-function mutations in DGKε cause atypical hemolytic-uremic syndrome (aHUS). This condition is characterized by thrombosis in the small vessels of the kidney. It causes acute renal insufficiency in infancy and most patients develop end-stage renal failure before adulthood. Disease pathophysiology is poorly understood and there is no therapy. There are also data suggesting that DGKε may play a role in epilepsy and Huntington disease. Thus, DGKε has many unique molecular and biochemical properties when compared to all other DGK isoforms. DGKε homologs also contain a number of conserved sequence features that are distinctive characteristics of either the rodents or specific groups of primate homologs. How cells, tissues and organisms harness DGKε's catalytic prowess remains unclear. The discovery of DGKε's role in causing aHUS will hopefully boost efforts to unravel the mechanisms by which DGKε dysfunction causes disease.
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Affiliation(s)
- Richard M Epand
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Vincent So
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences CentreHamilton, ON, Canada; Nephrology Division and Cell Biology Program, Hospital for Sick ChildrenToronto, ON, Canada
| | - William Jennings
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Bijendra Khadka
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Radhey S Gupta
- Department of Biochemistry and Biomedical Sciences, McMaster University Health Sciences Centre Hamilton, ON, Canada
| | - Mathieu Lemaire
- Nephrology Division and Cell Biology Program, Hospital for Sick ChildrenToronto, ON, Canada; Department of Biochemistry, University of TorontoToronto, ON, Canada; Institute of Medicine, University of TorontoToronto, ON, Canada
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Molecular properties of diacylglycerol kinase-epsilon in relation to function. Chem Phys Lipids 2015; 192:100-108. [PMID: 26134136 DOI: 10.1016/j.chemphyslip.2015.06.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 06/21/2015] [Indexed: 01/12/2023]
Abstract
The epsilon isoform of mammalian diacylglycerol kinase (DGKϵ) is an enzyme that associates strongly with membranes and acts on a lipid substrate, diacylglycerol. The protein has one segment that is predicted to be a transmembrane helix, but appears to interconvert between a transmembrane helix and a re-entrant helix. Despite the hydrophobicity of this segment and the fact that the lipid substrate is also hydrophobic, removal of this hydrophobic segment by truncating the protein at the amino terminus has no effect on its enzymatic activity. The amino acid sequence of the catalytic segment of DGKϵ is highly homologous to that of a bacterial DGK, DgkB. This has allowed us to predict a conformation of DGKϵ based on the known crystal structure of DgkB. An important property of DGKϵ is that it is specific for diacylglycerol species containing an arachidonoyl group. The region of DGKϵ that interacts with this group is found within the accessory domain of the protein and not in the active site nor in the hydrophobic amino terminus. The nature of the acyl chain specificity of the enzyme indicates that DGKϵ is associated with the synthesis of phosphatidylinositol. Defects or deletion of the enzyme give rise to several disease states.
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Petro EJ, Raben DM. Bacterial expression strategies for several Sus scrofa diacylglycerol kinase alpha constructs: solubility challenges. Sci Rep 2013; 3:1609. [PMID: 23558375 PMCID: PMC3617429 DOI: 10.1038/srep01609] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 03/19/2013] [Indexed: 01/27/2023] Open
Abstract
We pursued several strategies for expressing either full-length Sus scrofa diacylglycerol kinase (DGK) alpha or the catalytic domain (alphacat) in Escherichia coli. Alphacat could be extracted, refolded, and purified from inclusion bodies, but when subjected to analytical gel filtration chromatography, it elutes in the void volume, in what we conclude are microscopic aggregates unsuitable for x-ray crystallography. Adding glutathione S-transferase, thioredoxin, or maltose binding protein as N-terminal fusion tags did not improve alphacat's solubility. Coexpressing with bacterial chaperones increased the yield of alphacat in the supernatant after high-speed centrifugation, but the protein still elutes in the void upon analytical gel filtration chromatography. We believe our work will be of interest to those interested in the structure of eukaryotic DGKs, so that they know which expression strategies have already been tried, as well as to those interested in protein folding and those interested in chaperone/target-protein interactions.
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Affiliation(s)
- Elizabeth J. Petro
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD
| | - Daniel M. Raben
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD
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