1
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Shin SM, Itson-Zoske B, Fan F, Xiao Y, Qiu C, Cummins TR, Hogan QH, Yu H. Peripherally targeted analgesia via AAV-mediated sensory neuron-specific inhibition of multiple pronociceptive sodium channels. J Clin Invest 2024; 134:e170813. [PMID: 38722683 PMCID: PMC11213509 DOI: 10.1172/jci170813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 05/07/2024] [Indexed: 06/30/2024] Open
Abstract
This study reports that targeting intrinsically disordered regions of the voltage-gated sodium channel 1.7 (NaV1.7) protein facilitates discovery of sodium channel inhibitory peptide aptamers (NaViPA) for adeno-associated virus-mediated (AAV-mediated), sensory neuron-specific analgesia. A multipronged inhibition of INa1.7, INa1.6, INa1.3, and INa1.1 - but not INa1.5 and INa1.8 - was found for a prototype and named NaViPA1, which was derived from the NaV1.7 intracellular loop 1, and is conserved among the TTXs NaV subtypes. NaViPA1 expression in primary sensory neurons (PSNs) of dorsal root ganglia (DRG) produced significant inhibition of TTXs INa but not TTXr INa. DRG injection of AAV6-encoded NaViPA1 significantly attenuated evoked and spontaneous pain behaviors in both male and female rats with neuropathic pain induced by tibial nerve injury (TNI). Whole-cell current clamp of the PSNs showed that NaViPA1 expression normalized PSN excitability in TNI rats, suggesting that NaViPA1 attenuated pain by reversal of injury-induced neuronal hypersensitivity. IHC revealed efficient NaViPA1 expression restricted in PSNs and their central and peripheral terminals, indicating PSN-restricted AAV biodistribution. Inhibition of sodium channels by NaViPA1 was replicated in the human iPSC-derived sensory neurons. These results summate that NaViPA1 is a promising analgesic lead that, combined with AAV-mediated PSN-specific block of multiple TTXs NaVs, has potential as a peripheral nerve-restricted analgesic therapeutic.
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Affiliation(s)
- Seung Min Shin
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Brandon Itson-Zoske
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Fan Fan
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, Georgia, USA
| | - Yucheng Xiao
- Department of Biology, School of Science, Indiana University-Purdue University, Indianapolis, Indiana, USA
| | - Chensheng Qiu
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
- Department of Orthopedic Surgery, Qingdao Municipal Hospital, Qingdao, China
| | - Theodore R. Cummins
- Department of Biology, School of Science, Indiana University-Purdue University, Indianapolis, Indiana, USA
| | - Quinn H. Hogan
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Hongwei Yu
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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2
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Foster J, McPhee M, Yue L, Dellaire G, Pelech S, Ridgway ND. Lipid- and phospho-regulation of CTP:Phosphocholine Cytidylyltransferase α association with nuclear lipid droplets. Mol Biol Cell 2024; 35:ar33. [PMID: 38170618 PMCID: PMC10916874 DOI: 10.1091/mbc.e23-09-0354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 12/12/2023] [Accepted: 12/19/2023] [Indexed: 01/05/2024] Open
Abstract
Fatty acids stored in triacylglycerol-rich lipid droplets are assembled with a surface monolayer composed primarily of phosphatidylcholine (PC). Fatty acids stimulate PC synthesis by translocating CTP:phosphocholine cytidylyltransferase (CCT) α to the inner nuclear membrane, nuclear lipid droplets (nLD) and lipid associated promyelocytic leukemia (PML) structures (LAPS). Huh7 cells were used to identify how CCTα translocation onto these nuclear structures are regulated by fatty acids and phosphorylation of its serine-rich P-domain. Oleate treatment of Huh7 cells increased nLDs and LAPS that became progressively enriched in CCTα. In cells expressing the phosphatidic acid phosphatase Lipin1α or 1β, the expanded pool of nLDs and LAPS had a proportional increase in associated CCTα. In contrast, palmitate induced few nLDs and LAPS and inhibited the oleate-dependent translocation of CCTα without affecting total nLDs. Phospho-memetic or phospho-null mutations in the P-domain revealed that a 70% phosphorylation threshold, rather than site-specific phosphorylation, regulated CCTα association with nLDs and LAPS. In vitro candidate kinase and inhibitor studies in Huh7 cells identified cyclin-dependent kinase (CDK) 1 and 2 as putative P-domain kinases. In conclusion, CCTα translocation onto nLDs and LAPS is dependent on available surface area and fatty acid composition, as well as threshold phosphorylation of the P-domain potentially involving CDKs.
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Affiliation(s)
- Jason Foster
- Departments of Pediatrics and Biochemistry & Molecular Biology, Atlantic Research Centre, and
| | - Michael McPhee
- Departments of Pediatrics and Biochemistry & Molecular Biology, Atlantic Research Centre, and
| | - Lambert Yue
- Division of Neurology, Department of Medicine, University of British Columbia, Vancouver, BC, Canada V6T 2B5
| | - Graham Dellaire
- Departments of Pathology and Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H4R2
| | - Steven Pelech
- Division of Neurology, Department of Medicine, University of British Columbia, Vancouver, BC, Canada V6T 2B5
- Kinexus Bioinformatics Corporation, Vancouver, BC, Canada V6P 6T3
| | - Neale D. Ridgway
- Departments of Pediatrics and Biochemistry & Molecular Biology, Atlantic Research Centre, and
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3
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Liu X, Giarola V, Quan W, Song X, Bartels D. Identification and characterization of CTP:phosphocholine cytidylyltransferase CpCCT1 in the resurrection plant Craterostigma plantagineum. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2021; 302:110698. [PMID: 33288011 DOI: 10.1016/j.plantsci.2020.110698] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 09/08/2020] [Accepted: 10/02/2020] [Indexed: 06/12/2023]
Abstract
Phosphatidylcholine is a major phospholipid which is shown to be involved in stress adaptation. Phosphatidylcholine increased during dehydration in Craterostigma plantagineum, and therefore we characterized CTP:phosphocholine cytidylyltransferase (CpCCT1), a key regulatory enzyme for phosphatidylcholine synthesis in plants. The CpCCT1 gene from the resurrection plant C. plantagineum was cloned and the amino acid sequence was compared with homologs from other species including yeast and rat. CCT proteins have conserved catalytic and membrane-binding domains while the N-terminal and C-terminal domains have diverged. The tissue specific expression analysis indicated that CpCCT1 is expressed in all tested tissues and it is induced by dehydration and in response to 0.5 M NaCl solutions. In plants exposed to low temperature in the dark, the CpCCT1 transcript increased after 4 h at 4 °C. CpCCT1 expression also increased during mannitol and sorbitol treatments in a concentration dependent manner. Phytohormones such as abscisic acid and indole-3-acetic acid also trigged transcript accumulation. Comparisons of transcript and protein accumulations for different treatments (except for dehydration) suggest transcriptional and translational control mechanisms. Analysis of promoter activity and polysome occupancy suggest that CpCCT1 gene expression is mainly under translational regulation during dehydration.
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Affiliation(s)
- Xun Liu
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115, Bonn, Germany
| | - Valentino Giarola
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115, Bonn, Germany.
| | - Wenli Quan
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115, Bonn, Germany; Key Laboratory for Quality Control of Characteristic Fruits and Vegetables of Hubei Province, College of Life Science and Technology, Hubei Engineering University, Xiaogan, Hubei, 432000, China
| | - Xiaomin Song
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115, Bonn, Germany
| | - Dorothea Bartels
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115, Bonn, Germany.
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4
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Tavasoli M, Lahire S, Reid T, Brodovsky M, McMaster CR. Genetic diseases of the Kennedy pathways for membrane synthesis. J Biol Chem 2020; 295:17877-17886. [PMID: 33454021 PMCID: PMC7762932 DOI: 10.1074/jbc.rev120.013529] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 10/20/2020] [Indexed: 11/06/2022] Open
Abstract
The two branches of the Kennedy pathways (CDP-choline and CDP-ethanolamine) are the predominant pathways responsible for the synthesis of the most abundant phospholipids, phosphatidylcholine and phosphatidylethanolamine, respectively, in mammalian membranes. Recently, hereditary diseases associated with single gene mutations in the Kennedy pathways have been identified. Interestingly, genetic diseases within the same pathway vary greatly, ranging from muscular dystrophy to spastic paraplegia to a childhood blinding disorder to bone deformations. Indeed, different point mutations in the same gene (PCYT1; CCTα) result in at least three distinct diseases. In this review, we will summarize and review the genetic diseases associated with mutations in genes of the Kennedy pathway for phospholipid synthesis. These single-gene disorders provide insight, indeed direct genotype-phenotype relationships, into the biological functions of specific enzymes of the Kennedy pathway. We discuss potential mechanisms of how mutations within the same pathway can cause disparate disease.
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Affiliation(s)
- Mahtab Tavasoli
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Sarah Lahire
- University of Reims Champagne-Ardenne, Reims, France
| | - Taryn Reid
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Maren Brodovsky
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
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5
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Izrael R, Marton L, Nagy GN, Pálinkás HL, Kucsma N, Vértessy BG. Identification of a nuclear localization signal in the Plasmodium falciparum CTP: phosphocholine cytidylyltransferase enzyme. Sci Rep 2020; 10:19739. [PMID: 33184408 PMCID: PMC7665022 DOI: 10.1038/s41598-020-76829-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 11/02/2020] [Indexed: 12/30/2022] Open
Abstract
The phospholipid biosynthesis of the malaria parasite, Plasmodium falciparum is a key process for its survival and its inhibition is a validated antimalarial therapeutic approach. The second and rate-limiting step of the de novo phosphatidylcholine biosynthesis is catalysed by CTP: phosphocholine cytidylyltransferase (PfCCT), which has a key regulatory function within the pathway. Here, we investigate the functional impact of the key structural differences and their respective role in the structurally unique pseudo-heterodimer PfCCT protein in a heterologous cellular context using the thermosensitive CCT-mutant CHO-MT58 cell line. We found that a Plasmodium-specific lysine-rich insertion within the catalytic domain of PfCCT acts as a nuclear localization signal and its deletion decreases the nuclear propensity of the protein in the model cell line. We further showed that the putative membrane-binding domain also affected the nuclear localization of the protein. Moreover, activation of phosphatidylcholine biosynthesis by phospholipase C treatment induces the partial nuclear-to-cytoplasmic translocation of PfCCT. We additionally investigated the cellular function of several PfCCT truncated constructs in a CHO-MT58 based rescue assay. In absence of the endogenous CCT activity we observed that truncated constructs lacking the lysine-rich insertion, or the membrane-binding domain provided similar cell survival ratio as the full length PfCCT protein.
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Affiliation(s)
- Richard Izrael
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary.
- Doctoral School of Multidisciplinary Medical Sciences, University of Szeged, 6720, Szeged, Hungary.
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary.
| | - Lívia Marton
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
| | - Gergely N Nagy
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, OX3 7BN, UK
| | - Hajnalka L Pálinkás
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
- Doctoral School of Multidisciplinary Medical Sciences, University of Szeged, 6720, Szeged, Hungary
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary
| | - Nóra Kucsma
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
| | - Beáta G Vértessy
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary.
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary.
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6
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Cornell RB. Membrane Lipids Assist Catalysis by CTP: Phosphocholine Cytidylyltransferase. J Mol Biol 2020; 432:5023-5042. [PMID: 32234309 DOI: 10.1016/j.jmb.2020.03.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 03/22/2020] [Accepted: 03/25/2020] [Indexed: 02/06/2023]
Abstract
While most of the articles in this issue review the workings of integral membrane enzymes, in this review, we describe the catalytic mechanism of an enzyme that contains a soluble catalytic domain but appears to catalyze its reaction on the membrane surface, anchored and assisted by a separate regulatory amphipathic helical domain and inter-domain linker. Membrane partitioning of CTP: phosphocholine cytidylyltransferase (CCT), a key regulatory enzyme of phosphatidylcholine metabolism, is regulated chiefly by changes in membrane phospholipid composition, and boosts the enzyme's catalytic efficiency >200-fold. Catalytic enhancement by membrane binding involves the displacement of an auto-inhibitory helix from the active site entrance-way and promotion of a new conformational ensemble for the inter-domain, allosteric linker that has an active role in the catalytic cycle. We describe the evidence for close contact between membrane lipid, a compact allosteric linker, and the CCT active site, and discuss potential ways that this interaction enhances catalysis.
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Affiliation(s)
- Rosemary B Cornell
- Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada V5A-1S6.
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7
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Molecular Docking Reveals the Binding Modes of Anticancer Alkylphospholipids and Lysophosphatidylcholine within the Catalytic Domain of Cytidine Triphosphate: Phosphocholine Cytidyltransferase. EUR J LIPID SCI TECH 2020. [DOI: 10.1002/ejlt.201900422] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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8
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Yue L, McPhee MJ, Gonzalez K, Charman M, Lee J, Thompson J, Winkler DFH, Cornell RB, Pelech S, Ridgway ND. Differential dephosphorylation of CTP:phosphocholine cytidylyltransferase upon translocation to nuclear membranes and lipid droplets. Mol Biol Cell 2020; 31:1047-1059. [PMID: 32186954 PMCID: PMC7346725 DOI: 10.1091/mbc.e20-01-0014] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase-alpha (CCTα) and CCTβ catalyze the rate-limiting step in phosphatidylcholine (PC) biosynthesis. CCTα is activated by association of its α-helical M-domain with nuclear membranes, which is negatively regulated by phosphorylation of the adjacent P-domain. To understand how phosphorylation regulates CCT activity, we developed phosphosite-specific antibodies for pS319 and pY359+pS362 at the N- and C-termini of the P-domain, respectively. Oleate treatment of cultured cells triggered CCTα translocation to the nuclear envelope (NE) and nuclear lipid droplets (nLDs) and rapid dephosphorylation of pS319. Removal of oleate led to dissociation of CCTα from the NE and increased phosphorylation of S319. Choline depletion of cells also caused CCTα translocation to the NE and S319 dephosphorylation. In contrast, Y359 and S362 were constitutively phosphorylated during oleate addition and removal, and CCTα-pY359+pS362 translocated to the NE and nLDs of oleate-treated cells. Mutagenesis revealed that phosphorylation of S319 is regulated independently of Y359+S362, and that CCTα-S315D+S319D was defective in localization to the NE. We conclude that the P-domain undergoes negative charge polarization due to dephosphorylation of S319 and possibly other proline-directed sites and retention of Y359 and S362 phosphorylation, and that dephosphorylation of S319 and S315 is involved in CCTα recruitment to nuclear membranes.
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Affiliation(s)
- Lambert Yue
- Department of Medicine, Division of Neurology, University of British Columbia, Vancouver, BC V6T 2B5, Canada
| | - Michael J McPhee
- Department of Pediatrics and Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Kevin Gonzalez
- Department of Medicine, Division of Neurology, University of British Columbia, Vancouver, BC V6T 2B5, Canada
| | - Mark Charman
- Department of Pediatrics and Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Jonghwa Lee
- Department of Pediatrics and Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Jordan Thompson
- Department of Pediatrics and Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Dirk F H Winkler
- Kinexus Bioinformatics Corporation, Vancouver, BC V6P 6T3, Canada
| | - Rosemary B Cornell
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
| | - Steven Pelech
- Department of Medicine, Division of Neurology, University of British Columbia, Vancouver, BC V6T 2B5, Canada.,Kinexus Bioinformatics Corporation, Vancouver, BC V6P 6T3, Canada
| | - Neale D Ridgway
- Department of Pediatrics and Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
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9
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Knowles DG, Lee J, Taneva SG, Cornell RB. Remodeling of the interdomain allosteric linker upon membrane binding of CCTα pulls its active site close to the membrane surface. J Biol Chem 2019; 294:15531-15543. [PMID: 31488548 DOI: 10.1074/jbc.ra119.009850] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 08/18/2019] [Indexed: 01/10/2023] Open
Abstract
The rate-limiting step in the biosynthesis of the major membrane phospholipid, phosphatidylcholine, is catalyzed by CTP:phosphocholine cytidylyltransferase (CCT), which is regulated by reversible membrane binding of a long amphipathic helix (domain M). The M domain communicates with the catalytic domain via a conserved ∼20-residue linker, essential for lipid activation of CCT. Previous analysis of this region (denoted as the αEC/J) using MD simulations, cross-linking, mutagenesis, and solvent accessibility suggested that membrane binding of domain M promotes remodeling of the αEC/J into a more compact structure that is required for enzyme activation. Here, using tryptophan fluorescence quenching, we show that the allosteric linker lies superficially on the membrane surface. Analyses with truncated CCTs show that the αEC/J can interact with lipids independently of the M domain. We observed strong FRET between engineered tryptophans in the αEC/J and vesicles containing dansyl-phosphatidylethanolamine that depended on the native J sequence. These data are incompatible with the extended conformation of the αE helix observed in the previously determined crystal structure of inactive CCT but support a bent αE helix conformation stabilized by J segment interactions. Our results suggest that the membrane-adsorbed, folded allosteric linker may partially cover the active site cleft and pull it close to the membrane surface, where cytidyl transfer can occur efficiently in a relatively anhydrous environment.
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Affiliation(s)
- Daniel G Knowles
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Jaeyong Lee
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Svetla G Taneva
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Rosemary B Cornell
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada .,Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
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10
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Taneva SG, Lee J, Knowles DG, Tishyadhigama C, Chen H, Cornell RB. Interdomain communication in the phosphatidylcholine regulatory enzyme, CCTα, relies on a modular αE helix. J Biol Chem 2019; 294:15517-15530. [PMID: 31488547 DOI: 10.1074/jbc.ra119.009849] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 08/18/2019] [Indexed: 12/14/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT), the rate-limiting enzyme in phosphatidylcholine (PC) synthesis, is an amphitropic enzyme that regulates PC homeostasis. Recent work has suggested that CCTα activation by binding to a PC-deficient membrane involves conformational transitions in a helix pair (αE) that, along with a short linker of unknown structure (J segment), bridges the catalytic domains of the CCTα dimer to the membrane-binding (M) domains. In the soluble, inactive form, the αE helices are constrained into unbroken helices by contacts with two auto-inhibitory (AI) helices from domain M. In the active, membrane-bound form, the AI helices are displaced and engage the membrane. Molecular dynamics simulations have suggested that AI displacement is associated with hinge-like bending in the middle of the αE, positioning its C terminus closer to the active site. Here, we show that CCTα activation by membrane binding is sensitive to mutations in the αE and J segments, especially within or proximal to the αE hinge. Substituting Tyr-213 within this hinge with smaller uncharged amino acids that could destabilize interactions between the αE helices increased both constitutive and lipid-dependent activities, supporting a link between αE helix bending and stimulation of CCT activity. The solvent accessibilities of Tyr-213 and Tyr-216 suggested that these tyrosines move to new partially buried environments upon membrane binding of CCT, consistent with a folded αE/J structure. These data suggest that signal transduction through the modular αE helix pair relies on shifts in its conformational ensemble that are controlled by the AI helices and their displacement upon membrane binding.
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Affiliation(s)
- Svetla G Taneva
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Jaeyong Lee
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Daniel G Knowles
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Chanajai Tishyadhigama
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Hongwen Chen
- Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Rosemary B Cornell
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada .,Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
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11
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Cornell RB, Taneva SG, Dennis MK, Tse R, Dhillon RK, Lee J. Disease-linked mutations in the phosphatidylcholine regulatory enzyme CCTα impair enzymatic activity and fold stability. J Biol Chem 2018; 294:1490-1501. [PMID: 30559292 DOI: 10.1074/jbc.ra118.006457] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Revised: 12/05/2018] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT) is the key regulatory enzyme in phosphatidylcholine (PC) synthesis and is activated by binding to PC-deficient membranes. Mutations in the gene encoding CCTα (PCYT1A) cause three distinct pathologies in humans: lipodystrophy, spondylometaphyseal dysplasia with cone-rod dystrophy (SMD-CRD), and isolated retinal dystrophy. Previous analyses showed that for some disease-linked PCYT1A variants steady state levels of CCTα and PC synthesis were reduced in patient fibroblasts, but other variants impaired PC synthesis with little effect on CCT levels. To explore the impact on CCT stability and function we expressed WT and mutant CCTs in COS-1 cells, which have very low endogenous CCT. Over-expression of two missense variants in the catalytic domain (V142M and P150A) generated aggregated enzymes that could not be refolded after solubilization by denaturation. Other mutations in the catalytic core that generated CCTs with reduced solubility could be purified. Five variants destabilized the catalytic domain-fold as assessed by lower transition temperatures for unfolding, and three of these manifested defects in substrate Km values. A mutation (R223S) in a signal-transducing linker between the catalytic and membrane-binding domains also impaired enzyme kinetics. E280del, a single amino acid deletion in the autoinhibitory helix increased the constitutive (lipid-independent) enzyme activity ∼4-fold. This helix also participates in membrane binding, and surprisingly E280del enhanced the enzyme's response to anionic lipid vesicles ∼4-fold. These in vitro analyses on purified mutant CCTs will complement future measurements of their impact on PC synthesis in cultured cells and in tissues with a stringent requirement for CCTα.
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Affiliation(s)
- Rosemary B Cornell
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada; Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada.
| | - Svetla G Taneva
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada
| | - Melissa K Dennis
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada
| | - Ronnie Tse
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada
| | - Randeep K Dhillon
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada
| | - Jaeyong Lee
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 Canada
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12
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Ramezanpour M, Lee J, Taneva SG, Tieleman DP, Cornell RB. An auto-inhibitory helix in CTP:phosphocholine cytidylyltransferase hijacks the catalytic residue and constrains a pliable, domain-bridging helix pair. J Biol Chem 2018. [PMID: 29519816 DOI: 10.1074/jbc.ra118.002053] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activity of CTP:phosphocholine cytidylyltransferase (CCT), a key enzyme in phosphatidylcholine synthesis, is regulated by reversible interactions of a lipid-inducible amphipathic helix (domain M) with membrane phospholipids. When dissociated from membranes, a portion of the M domain functions as an auto-inhibitory (AI) element to suppress catalysis. The AI helix from each subunit binds to a pair of α helices (αE) that extend from the base of the catalytic dimer to create a four-helix bundle. The bound AI helices make intimate contact with loop L2, housing a key catalytic residue, Lys122 The impacts of the AI helix on active-site dynamics and positioning of Lys122 are unknown. Extensive MD simulations with and without the AI helix revealed that backbone carbonyl oxygens at the point of contact between the AI helix and loop L2 can entrap the Lys122 side chain, effectively competing with the substrate, CTP. In silico, removal of the AI helices dramatically increased αE dynamics at a predicted break in the middle of these helices, enabling them to splay apart and forge new contacts with loop L2. In vitro cross-linking confirmed the reorganization of the αE element upon membrane binding of the AI helix. Moreover, when αE bending was prevented by disulfide engineering, CCT activation by membrane binding was thwarted. These findings suggest a novel two-part auto-inhibitory mechanism for CCT involving capture of Lys122 and restraint of the pliable αE helices. We propose that membrane binding enables bending of the αE helices, bringing the active site closer to the membrane surface.
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Affiliation(s)
- Mohsen Ramezanpour
- From the Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4 and
| | - Jaeyong Lee
- the Departments of Molecular Biology and Biochemistry and
| | | | - D Peter Tieleman
- From the Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4 and
| | - Rosemary B Cornell
- the Departments of Molecular Biology and Biochemistry and .,Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
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13
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Chang CC, Few LL, Konrad M, See Too WC. Phosphorylation of Human Choline Kinase Beta by Protein Kinase A: Its Impact on Activity and Inhibition. PLoS One 2016; 11:e0154702. [PMID: 27149373 PMCID: PMC4858151 DOI: 10.1371/journal.pone.0154702] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 04/18/2016] [Indexed: 12/19/2022] Open
Abstract
Choline kinase beta (CKβ) is one of the CK isozymes involved in the biosynthesis of phosphatidylcholine. CKβ is important for normal mitochondrial function and muscle development as the lack of the ckβ gene in human and mice results in the development of muscular dystrophy. In contrast, CKα is implicated in tumorigenesis and has been extensively studied as an anticancer target. Phosphorylation of human CKα was found to regulate the enzyme’s activity and its subcellular location. This study provides evidence for CKβ phosphorylation by protein kinase A (PKA). In vitro phosphorylation of CKβ by PKA was first detected by phosphoprotein staining, as well as by in-gel kinase assays. The phosphorylating kinase was identified as PKA by Western blotting. CKβ phosphorylation by MCF-7 cell lysate was inhibited by a PKA-specific inhibitor peptide, and the intracellular phosphorylation of CKβ was shown to be regulated by the level of cyclic adenosine monophosphate (cAMP), a PKA activator. Phosphorylation sites were located on CKβ residues serine-39 and serine-40 as determined by mass spectrometry and site-directed mutagenesis. Phosphorylation increased the catalytic efficiencies for the substrates choline and ATP about 2-fold, without affecting ethanolamine phosphorylation, and the S39D/S40D CKβ phosphorylation mimic behaved kinetically very similar. Remarkably, phosphorylation drastically increased the sensitivity of CKβ to hemicholinium-3 (HC-3) inhibition by about 30-fold. These findings suggest that CKβ, in concert with CKα, and depending on its phosphorylation status, might play a critical role as a druggable target in carcinogenesis.
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Affiliation(s)
- Ching Ching Chang
- School of Health Sciences, Health Campus, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia
| | - Ling Ling Few
- School of Health Sciences, Health Campus, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia
| | - Manfred Konrad
- Enzyme Biochemistry Group, Max Planck Institute for Biophysical Chemistry, 37077, Goettingen, Germany
- * E-mail: (WCST); (MK)
| | - Wei Cun See Too
- School of Health Sciences, Health Campus, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia
- * E-mail: (WCST); (MK)
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14
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A transducible nuclear/nucleolar protein, mLLP, regulates neuronal morphogenesis and synaptic transmission. Sci Rep 2016; 6:22892. [PMID: 26961175 PMCID: PMC4790632 DOI: 10.1038/srep22892] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Accepted: 02/23/2016] [Indexed: 12/03/2022] Open
Abstract
Cell-permeable proteins are emerging as unconventional regulators of signal transduction and providing a potential for therapeutic applications. However, only a few of them are identified and studied in detail. We identify a novel cell-permeable protein, mouse LLP homolog (mLLP), and uncover its roles in regulating neural development. We found that mLLP is strongly expressed in developing nervous system and that mLLP knockdown or overexpression during maturation of cultured neurons affected the neuronal growth and synaptic transmission. Interestingly, extracellular addition of mLLP protein enhanced dendritic arborization, demonstrating the non-cell-autonomous effect of mLLP. Moreover, mLLP interacts with CCCTC-binding factor (CTCF) as well as transcriptional machineries and modulates gene expression involved in neuronal growth. Together, these results illustrate the characteristics and roles of previously unknown cell-permeable protein mLLP in modulating neural development.
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15
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Membrane lipid compositional sensing by the inducible amphipathic helix of CCT. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1861:847-861. [PMID: 26747646 DOI: 10.1016/j.bbalip.2015.12.022] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 12/22/2015] [Accepted: 12/29/2015] [Indexed: 11/21/2022]
Abstract
The amphipathic helical (AH) membrane binding motif is recognized as a major device for lipid compositional sensing. We explore the function and mechanism of sensing by the lipid biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase (CCT). As the regulatory enzyme in phosphatidylcholine (PC) synthesis, CCT contributes to membrane PC homeostasis. CCT directly binds and inserts into the surface of bilayers that are deficient in PC and therefore enriched in lipids that enhance surface charge and/or create lipid packing voids. These two membrane physical properties induce the folding of the CCT M domain into a ≥60 residue AH. Membrane binding activates catalysis by a mechanism that has been partially deciphered. We review the evidence for CCT compositional sensing, and the membrane and protein determinants for lipid selective membrane-interactions. We consider the factors that promote the binding of CCT isoforms to the membranes of the ER, nuclear envelope, or lipid droplets, but exclude CCT from other organelles and the plasma membrane. The CCT sensing mechanism is compared with several other proteins that use an AH motif for membrane compositional sensing. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
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16
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Cornell RB, Ridgway ND. CTP:phosphocholine cytidylyltransferase: Function, regulation, and structure of an amphitropic enzyme required for membrane biogenesis. Prog Lipid Res 2015; 59:147-71. [PMID: 26165797 DOI: 10.1016/j.plipres.2015.07.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Revised: 07/07/2015] [Accepted: 07/07/2015] [Indexed: 12/12/2022]
Abstract
CTP:phosphocholine cytidylyltransferase (CCT) catalyzes a rate-limiting and regulated step in the CDP-choline pathway for the synthesis of phosphatidylcholine (PC) and PC-derived lipids. Control of CCT activity is multi-layered, and includes direct regulation by reversible membrane binding involving a built-in lipid compositional sensor. Thus CCT contributes to phospholipid compositional homeostasis. CCT also modifies the curvature of its target membrane. Knowledge of CCT structure and regulation of its catalytic function are relatively advanced compared to many lipid metabolic enzymes, and are reviewed in detail. Recently the genetic origins of two human developmental and lipogenesis disorders have been traced to mutations in the gene for CCTα.
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Affiliation(s)
- Rosemary B Cornell
- Department of Molecular Biology and Biochemistry and the Department of Chemistry, Simon Fraser University, Burnaby, B.C. V5A-1S6, Canada.
| | - Neale D Ridgway
- Departments of Pediatrics, and Biochemistry and Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia B3H-4H7, Canada
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17
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Chong SSY, Taneva SG, Lee JMC, Cornell RB. The Curvature Sensitivity of a Membrane-Binding Amphipathic Helix Can Be Modulated by the Charge on a Flanking Region. Biochemistry 2014; 53:450-61. [DOI: 10.1021/bi401457r] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Sharon S. Y. Chong
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Svetla G. Taneva
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Joseph M. C. Lee
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Rosemary B. Cornell
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
- Department
of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
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18
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Lee J, Taneva SG, Holland BW, Tieleman DP, Cornell RB. Structural basis for autoinhibition of CTP:phosphocholine cytidylyltransferase (CCT), the regulatory enzyme in phosphatidylcholine synthesis, by its membrane-binding amphipathic helix. J Biol Chem 2013; 289:1742-55. [PMID: 24275660 DOI: 10.1074/jbc.m113.526970] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT) interconverts between an inactive soluble and active membrane-bound form in response to changes in membrane lipid composition. Activation involves disruption of an inhibitory interaction between the αE helices at the base of the active site and an autoinhibitory (AI) segment in the regulatory M domain and membrane insertion of the M domain as an amphipathic helix. We show that in the CCT soluble form the AI segment functions to suppress kcat and elevate the Km for CTP. The crystal structure of a CCT dimer composed of the catalytic and AI segments reveals an AI-αE interaction as a cluster of four amphipathic helices (two αE and two AI helices) at the base of the active sites. This interaction corroborates mutagenesis implicating multiple hydrophobic residues within the AI segment that contribute to its silencing function. The AI-αE interaction directs the turn at the C-terminal end of the AI helix into backbone-to-backbone contact with a loop (L2) at the opening to the active site, which houses the key catalytic residue, lysine 122. Molecular dynamics simulations suggest that lysine 122 side-chain orientations are constrained by contacts with the AI helix-turn, which could obstruct its engagement with substrates. This work deciphers how the CCT regulatory amphipathic helix functions as a silencing device.
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Affiliation(s)
- Jaeyong Lee
- From the Departments of Molecular Biology and Biochemistry and
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19
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Ridgway ND. The role of phosphatidylcholine and choline metabolites to cell proliferation and survival. Crit Rev Biochem Mol Biol 2013; 48:20-38. [PMID: 23350810 DOI: 10.3109/10409238.2012.735643] [Citation(s) in RCA: 206] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.
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Affiliation(s)
- Neale D Ridgway
- Departments of Pediatrics and Biochemistry & Molecular Biology, The Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia Canada.
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20
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Cardozo Gizzi AM, Caputto BL. Mechanistic insights into the nongenomic regulation of phospholipid synthesizing enzymes. IUBMB Life 2013; 65:584-92. [PMID: 23712998 DOI: 10.1002/iub.1173] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 03/21/2013] [Indexed: 11/06/2022]
Abstract
Lipid synthesis is a complex process regulated at multiple levels. Here, we will discuss nongenomic regulatory mechanisms, particularly the activation and/or recruitment of key enzymes to membranes. The phospholipid synthesis enzymes Lipin and CTP:phosphocholine cytidylyltransferase are taken as examples of these mechanisms that are mediated by posttranslational modifications or by an intrinsic property of the enzyme that senses lipid composition. In addition, special emphasis will be put on another relevant non genomic lipid synthesis regulation mechanism that is dependent on c-Fos, a protein that has deserved less attention so far. This latter regulatory mechanism is emerging as an important determinant for processes that require high rates of lipid synthesis such as those of growth and proliferation.
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Affiliation(s)
- Andrés M Cardozo Gizzi
- Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC (UNC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
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21
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Lagace TA, Ridgway ND. The role of phospholipids in the biological activity and structure of the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2499-510. [PMID: 23711956 DOI: 10.1016/j.bbamcr.2013.05.018] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 05/09/2013] [Accepted: 05/15/2013] [Indexed: 01/22/2023]
Abstract
The endoplasmic reticulum (ER) is an interconnected network of tubular and planar membranes that supports the synthesis and export of proteins, carbohydrates and lipids. Phospholipids, in particular phosphatidylcholine (PC), are synthesized in the ER where they have essential functions including provision of membranes required for protein synthesis and export, cholesterol homeostasis, and triacylglycerol storage and secretion. Coordination of these biological processes is essential, as highlighted by findings that link phospholipid metabolism in the ER with perturbations in lipid storage/secretion and stress responses, ultimately contributing to obesity/diabetes, atherosclerosis and neurological disorders. Phospholipid synthesis is not uniformly distributed in the ER but is localized at membrane interfaces or contact zones with other organelles, and in dynamic, proliferating ER membranes. The topology of phospholipid synthesis is an important consideration when establishing the etiology of diseases that arise from ER dysfunction. This review will highlight our current understanding of the contribution of phospholipid synthesis to proper ER function, and how alterations contribute to aberrant stress responses and disease. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Thomas A Lagace
- University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
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22
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Uversky VN. The most important thing is the tail: multitudinous functionalities of intrinsically disordered protein termini. FEBS Lett 2013; 587:1891-901. [PMID: 23665034 DOI: 10.1016/j.febslet.2013.04.042] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 04/24/2013] [Accepted: 04/29/2013] [Indexed: 01/29/2023]
Abstract
Many functional proteins do not have well-folded structures in their substantial parts, representing hybrids that possess both ordered and disordered regions. Disorder is unevenly distributed within these hybrid proteins and is typically more common at protein termini. Disordered tails are engaged in a wide range of functions, some of which are unique for termini and cannot be found in other disordered parts of a protein. This review covers some of the key functions of disordered protein termini and emphasizes that these tails are not simple flexible protrusions but are evolved to serve.
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine, USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
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23
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Bórquez DA, Olmos C, Álvarez S, Di Genova A, Maass A, González-Billault C. Bioinformatic survey for new physiological substrates of Cyclin-dependent kinase 5. Genomics 2013; 101:221-8. [DOI: 10.1016/j.ygeno.2013.01.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 12/26/2012] [Accepted: 01/26/2013] [Indexed: 11/27/2022]
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24
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Huang HKH, Taneva SG, Lee J, Silva LP, Schriemer DC, Cornell RB. The membrane-binding domain of an amphitropic enzyme suppresses catalysis by contact with an amphipathic helix flanking its active site. J Mol Biol 2012; 425:1546-64. [PMID: 23238251 DOI: 10.1016/j.jmb.2012.12.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 11/24/2012] [Accepted: 12/03/2012] [Indexed: 11/29/2022]
Abstract
CTP:phosphocholine cytidylyltransferase (CCT), the regulatory enzyme in the synthesis of phosphatidylcholine, is activated by binding membranes using a lipid-induced amphipathic helix (domain M). Domain M functions to silence catalysis when CCT is not membrane engaged. The silencing mechanism is unknown. We used photo-cross-linking and mass spectrometry to identify contacts between domain M and other CCT domains in its soluble form. Each of four sites in domain M forged cross-links to the same set of peptides that flank the active site and overlap at helix αE at the base of the active site. These cross-links were broken in the presence of activating lipid vesicles. Mutagenesis of domain M revealed that multiple hydrophobic residues within a putative auto-inhibitory (AI) motif contribute to the contact with helix αE and silencing. Helix αE was confirmed as the docking site for domain M by deuterium exchange analysis. We compared the dynamics and fold stability of CCT domains by site-directed fluorescence anisotropy and urea denaturation. The results suggest a bipartite structure for domain M: a disordered N-terminal portion and an ordered C-terminal AI motif with an unfolding transition identical with that of helix αE. Reduction in hydrophobicity of the AI motif decreased its order and fold stability, as did deletion of the catalytic domain. These results support a model in which catalytic silencing is mediated by the docking of an amphipathic AI motif onto the amphipathic helices αE. An unstructured leash linking αE with the AI motif may facilitate both the silencing contact and its membrane-triggered disruption.
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Affiliation(s)
- Harris K-H Huang
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
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25
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Agassandian M, Mallampalli RK. Surfactant phospholipid metabolism. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:612-25. [PMID: 23026158 DOI: 10.1016/j.bbalip.2012.09.010] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 09/07/2012] [Accepted: 09/16/2012] [Indexed: 12/16/2022]
Abstract
Pulmonary surfactant is essential for life and is composed of a complex lipoprotein-like mixture that lines the inner surface of the lung to prevent alveolar collapse at the end of expiration. The molecular composition of surfactant depends on highly integrated and regulated processes involving its biosynthesis, remodeling, degradation, and intracellular trafficking. Despite its multicomponent composition, the study of surfactant phospholipid metabolism has focused on two predominant components, disaturated phosphatidylcholine that confers surface-tension lowering activities, and phosphatidylglycerol, recently implicated in innate immune defense. Future studies providing a better understanding of the molecular control and physiological relevance of minor surfactant lipid components are needed. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
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Affiliation(s)
- Marianna Agassandian
- Department of Medicine, Acute Lung Injury Center of Excellence, the University of Pittsburgh, Pittsburgh, PA 15213, USA
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26
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Phosphatidylcholine and the CDP-choline cycle. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:523-32. [PMID: 23010477 DOI: 10.1016/j.bbalip.2012.09.009] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Accepted: 09/16/2012] [Indexed: 11/20/2022]
Abstract
The CDP-choline pathway of phosphatidylcholine (PtdCho) biosynthesis was first described more than 50 years ago. Investigation of the CDP-choline pathway in yeast provides a basis for understanding the CDP-choline pathway in mammals. PtdCho is considered as an intermediate in a cycle of synthesis and degradation, and the activity of a CDP-choline cycle is linked to subcellular membrane lipid movement. The components of the mammalian CDP-choline pathway include choline transport, choline kinase, phosphocholine cytidylyltransferase, and choline phosphotransferase activities. The protein isoforms and biochemical mechanisms of regulation of the pathway enzymes are related to their cell- and tissue-specific functions. Regulated PtdCho turnover mediated by phospholipases or neuropathy target esterase participates in the mammalian CDP-choline cycle. Knockout mouse models define the biological functions of the CDP-choline cycle in mammalian cells and tissues. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
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27
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Ding Z, Taneva SG, Huang HKH, Campbell SA, Semenec L, Chen N, Cornell RB. A 22-mer segment in the structurally pliable regulatory domain of metazoan CTP: phosphocholine cytidylyltransferase facilitates both silencing and activating functions. J Biol Chem 2012; 287:38980-91. [PMID: 22988242 DOI: 10.1074/jbc.m112.402081] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT), an amphitropic enzyme that regulates phosphatidylcholine synthesis, is composed of a catalytic head domain and a regulatory tail. The tail region has dual functions as a regulator of membrane binding/enzyme activation and as an inhibitor of catalysis in the unbound form of the enzyme, suggesting conformational plasticity. These functions are well conserved in CCTs across diverse phyla, although the sequences of the tail regions are not. CCT regulatory tails of diverse origins are composed of a long membrane lipid-inducible amphipathic helix (m-AH) followed by a highly disordered segment, reminiscent of the Parkinson disease-linked protein, α-synuclein, which we show shares a novel sequence motif with vertebrate CCTs. To unravel features required for silencing, we created chimeric enzymes by fusing the catalytic domain of rat CCTα to the regulatory tail of CCTs from Drosophila, Caenorhabditis elegans, or Saccharomyces cerevisiae or to α-synuclein. Only the tail domains of the two invertebrate CCTs were competent for both suppression of catalytic activity and for activation by lipid vesicles. Thus, both silencing and activating functions of the m-AH can tolerate significant changes in length and sequence. We identified a highly amphipathic 22-residue segment in the m-AH with features conserved among animal CCTs but not yeast CCT or α-synuclein. Deletion of this segment from rat CCT increased the lipid-independent V(max) by 10-fold, equivalent to the effect of deleting the entire tail, and severely weakened membrane binding affinity. However, membrane binding was required for additional increases in catalytic efficiency. Thus, full activation of CCT may require not only loss of a silencing conformation in the m-AH but a gain of an activating conformation, promoted by membrane binding.
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Affiliation(s)
- Ziwei Ding
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
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28
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The amphipathic helix of an enzyme that regulates phosphatidylcholine synthesis remodels membranes into highly curved nanotubules. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1173-86. [DOI: 10.1016/j.bbamem.2012.01.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 01/09/2012] [Accepted: 01/10/2012] [Indexed: 11/20/2022]
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29
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Kupke T, Di Cecco L, Müller HM, Neuner A, Adolf F, Wieland F, Nickel W, Schiebel E. Targeting of Nbp1 to the inner nuclear membrane is essential for spindle pole body duplication. EMBO J 2011; 30:3337-52. [PMID: 21785410 DOI: 10.1038/emboj.2011.242] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 06/30/2011] [Indexed: 12/29/2022] Open
Abstract
Spindle pole bodies (SPBs), like nuclear pore complexes, are embedded in the nuclear envelope (NE) at sites of fusion of the inner and outer nuclear membranes. A network of interacting proteins is required to insert a cytoplasmic SPB precursor into the NE. A central player of this network is Nbp1 that interacts with the conserved integral membrane protein Ndc1. Here, we establish that Nbp1 is a monotopic membrane protein that is essential for SPB insertion at the inner face of the NE. In vitro and in vivo studies identified an N-terminal amphipathic α-helix of Nbp1 as a membrane-binding element, with crucial functions in SPB duplication. The karyopherin Kap123 binds to a nuclear localization sequence next to this amphipathic α-helix and prevents unspecific tethering of Nbp1 to membranes. After transport into the nucleus, Nbp1 binds to the inner nuclear membrane. These data define the targeting pathway of a SPB component and suggest that the amphipathic α-helix of Nbp1 is important for SPB insertion into the NE from within the nucleus.
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Affiliation(s)
- Thomas Kupke
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany
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