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Malvezzi M, Andra KK, Pandey K, Lee BC, Falzone ME, Brown A, Iqbal R, Menon AK, Accardi A. Out-of-the-groove transport of lipids by TMEM16 and GPCR scramblases. Proc Natl Acad Sci U S A 2018; 115:E7033-E7042. [PMID: 29925604 PMCID: PMC6065010 DOI: 10.1073/pnas.1806721115] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phospholipid scramblases externalize phosphatidylserine to facilitate numerous physiological processes. Several members of the structurally unrelated TMEM16 and G protein-coupled receptor (GPCR) protein families mediate phospholipid scrambling. The structure of a TMEM16 scramblase shows a membrane-exposed hydrophilic cavity, suggesting that scrambling occurs via the ‟credit-card" mechanism where lipid headgroups permeate through the cavity while their tails remain associated with the membrane core. Here we show that afTMEM16 and opsin, representatives of the TMEM16 and GCPR scramblase families, transport phospholipids with polyethylene glycol headgroups whose globular dimensions are much larger than the width of the cavity. This suggests that transport of these large headgroups occurs outside rather than within the cavity. These large lipids are scrambled at rates comparable to those of normal phospholipids and their presence in the reconstituted vesicles promotes scrambling of normal phospholipids. This suggests that both large and small phospholipids can move outside the cavity. We propose that the conformational rearrangements underlying TMEM16- and GPCR-mediated credit-card scrambling locally deform the membrane to allow transbilayer lipid translocation outside the cavity and that both mechanisms underlie transport of normal phospholipids.
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Affiliation(s)
- Mattia Malvezzi
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065
| | - Kiran K Andra
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Kalpana Pandey
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Byoung-Cheol Lee
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065
| | - Maria E Falzone
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Ashley Brown
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Rabia Iqbal
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
| | - Alessio Accardi
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065;
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY 10065
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52
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Falzone ME, Malvezzi M, Lee BC, Accardi A. Known structures and unknown mechanisms of TMEM16 scramblases and channels. J Gen Physiol 2018; 150:933-947. [PMID: 29915161 PMCID: PMC6028493 DOI: 10.1085/jgp.201711957] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 05/29/2018] [Indexed: 12/25/2022] Open
Abstract
Falzone et al. interpret the mechanisms underlying the activity of TMEM16 family members from recent structural and functional work. The TMEM16 family of membrane proteins is composed of both Ca2+-gated Cl− channels and Ca2+-dependent phospholipid scramblases. The functional diversity of TMEM16s underlies their involvement in numerous signal transduction pathways that connect changes in cytosolic Ca2+ levels to cellular signaling networks. Indeed, defects in the function of several TMEM16s cause a variety of genetic disorders, highlighting their fundamental pathophysiological importance. Here, we review how our mechanistic understanding of TMEM16 function has been shaped by recent functional and structural work. Remarkably, the recent determination of near-atomic-resolution structures of TMEM16 proteins of both functional persuasions has revealed how relatively minimal rearrangements in the substrate translocation pathway are sufficient to precipitate the dramatic functional differences that characterize the family. These structures, when interpreted in the light of extensive functional analysis, point to an unusual mechanism for Ca2+-dependent activation of TMEM16 proteins in which substrate permeation is regulated by a combination of conformational rearrangements and electrostatics. These breakthroughs pave the way to elucidate the mechanistic bases of ion and lipid transport by the TMEM16 proteins and unravel the molecular links between these transport activities and their function in human pathophysiology.
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Affiliation(s)
- Maria E Falzone
- Department of Biochemistry, Weill Cornell Medical School, New York, NY
| | - Mattia Malvezzi
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY
| | - Byoung-Cheol Lee
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY
| | - Alessio Accardi
- Department of Biochemistry, Weill Cornell Medical School, New York, NY .,Department of Anesthesiology, Weill Cornell Medical School, New York, NY.,Department of Physiology, Biophysics and Systems Biology, Weill Cornell Medical School, New York, NY
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53
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Andra KK, Dorsey S, Royer CA, Menon AK. Structural mapping of fluorescently-tagged, functional nhTMEM16 scramblase in a lipid bilayer. J Biol Chem 2018; 293:12248-12258. [PMID: 29903908 DOI: 10.1074/jbc.ra118.003648] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 06/12/2018] [Indexed: 01/25/2023] Open
Abstract
Most members of the TransMEMbrane protein 16 (TMEM16) family are Ca2+-regulated scramblases that facilitate the bidirectional movement of phospholipids across membranes necessary for diverse physiological processes. The nhTMEM16 scramblase (from the fungus Nectria hematococca) is a homodimer with a large cytoplasmic region and a hydrophilic, membrane-exposed groove in each monomer. The groove provides the transbilayer conduit for lipids, but the mechanism by which Ca2+ regulates it is not clear. Because fusion of large protein tags at either the N or C terminus abolishes nhTMEM16 activity, we hypothesized that its cytoplasmic portion containing both termini may regulate lipid translocation via a Ca2+-dependent conformational change. To test this hypothesis, here we used fluorescence methods to map key distances within the nhTMEM16 homodimer and between its termini and the membrane. To this end, we developed functional nhTMEM16 variants bearing an acyl carrier protein (ACP) tag at one or both of the termini. These constructs were fluorescently labeled by ACP synthase-mediated insertion of CoA-conjugated fluorophores and reconstituted into vesicles containing fluorescent lipids to obtain the distance of closest approach between the labeled tag and the membrane via FRET. Fluorescence lifetime measurements with phasor analysis were used to determine the distance between the N and C termini of partnering monomers in the nhTMEM16 homodimer. We now report that the measured distances do not vary significantly between Ca2+-replete and EGTA-treated samples, indicating that whereas the cytoplasmic portion of the protein is important for function, it does not appear to regulate scramblase activity via a detectable conformational change.
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Affiliation(s)
- Kiran K Andra
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065
| | - Savanna Dorsey
- Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Catherine A Royer
- Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065.
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54
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Kumar S, Calianese D, Birge RB. Efferocytosis of dying cells differentially modulate immunological outcomes in tumor microenvironment. Immunol Rev 2018; 280:149-164. [PMID: 29027226 DOI: 10.1111/imr.12587] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Programmed cell death (apoptosis) is an integral part of tissue homeostasis in complex organisms, allowing for tissue turnover, repair, and renewal while simultaneously inhibiting the release of self antigens and danger signals from apoptotic cell-derived constituents that can result in immune activation, inflammation, and autoimmunity. Unlike cells in culture, the physiological fate of cells that die by apoptosis in vivo is their rapid recognition and engulfment by phagocytic cells (a process called efferocytosis). To this end, apoptotic cells express specific eat-me signals, such as externalized phosphatidylserine (PS), that are recognized in a specific context by receptors to initiate signaling pathways for engulfment. The importance of carefully regulated recognition and clearance pathways is evident in the spectrum of inflammatory and autoimmune disorders caused by defects in PS receptors and signaling molecules. However, in recent years, several additional cell death pathways have emerged, including immunogenic cell death, necroptosis, pyroptosis, and netosis that interweave different cell death pathways with distinct innate and adaptive responses from classical apoptosis that can shape long-term host immunity. In this review, we discuss the role of different cell death pathways in terms of their immune potential outcomes specifically resulting in specific cell corpse/phagocyte interactions (phagocytic synapses) that impinge on host immunity, with a main emphasis on tolerance and cancer immunotherapy.
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Affiliation(s)
- Sushil Kumar
- New Jersey Medical School, Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University, Newark, NJ, USA
| | - David Calianese
- New Jersey Medical School, Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University, Newark, NJ, USA
| | - Raymond B Birge
- New Jersey Medical School, Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University, Newark, NJ, USA
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55
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Di Zanni E, Gradogna A, Scholz-Starke J, Boccaccio A. Gain of function of TMEM16E/ANO5 scrambling activity caused by a mutation associated with gnathodiaphyseal dysplasia. Cell Mol Life Sci 2018; 75:1657-1670. [PMID: 29124309 PMCID: PMC5897490 DOI: 10.1007/s00018-017-2704-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/10/2017] [Accepted: 10/30/2017] [Indexed: 12/31/2022]
Abstract
Mutations in the human TMEM16E (ANO5) gene are associated both with the bone disease gnathodiaphyseal dysplasia (GDD; OMIM: 166260) and muscle dystrophies (OMIM: 611307, 613319). However, the physiological function of TMEM16E has remained unclear. We show here that human TMEM16E, when overexpressed in mammalian cell lines, displayed partial plasma membrane localization and gave rise to phospholipid scrambling (PLS) as well as non-selective ionic currents with slow time-dependent activation at highly depolarized membrane potentials. While the activity of wild-type TMEM16E depended on elevated cytosolic Ca2+ levels, a mutant form carrying the GDD-causing T513I substitution showed PLS and large time-dependent ion currents even at low cytosolic Ca2+ concentrations. Contrarily, mutation of the homologous position in the Ca2+-activated Cl- channel TMEM16B paralog hardly affected its function. In summary, these data provide the first direct demonstration of Ca2+-dependent PLS activity for TMEM16E and suggest a gain-of-function phenotype related to a GDD mutation.
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Affiliation(s)
- Eleonora Di Zanni
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy
| | - Antonella Gradogna
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy
| | - Joachim Scholz-Starke
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy.
| | - Anna Boccaccio
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy.
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56
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Abstract
Membrane biology seeks to understand how lipids and proteins within bilayers assemble into large structures such as organelles and the plasma membranes. Historically, lipids were thought to merely provide structural support for bilayer formation and membrane protein function. Research has now revealed that phospholipid metabolism regulates nearly all cellular processes. Sophisticated techniques helped identify >10,000 lipid species suggesting that lipids support many biological processes. Here, we highlight the synthesis of the most abundant glycerophospholipid classes and their distribution in organelles. We review vesicular and nonvesicular transport pathways shuttling lipids between organelles and discuss lipid regulators of membrane trafficking and second messengers in eukaryotic cells.
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Affiliation(s)
- Yanbo Yang
- From the Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario M5B 1W8.,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, and
| | - Minhyoung Lee
- From the Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario M5B 1W8.,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, and
| | - Gregory D Fairn
- From the Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario M5B 1W8, .,the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, and.,the Department of Surgery, University of Toronto, Toronto, Ontario M5T 1P5, Canada
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57
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Abstract
Transmembrane protein 16F (TMEM16F) is a Ca2+-dependent phospholipid scramblase that translocates phospholipids bidirectionally between the leaflets of the plasma membrane. Phospholipid scrambling of TMEM16F causes exposure of phosphatidylserine in activated platelets to induce blood clotting and in differentiated osteoblasts to promote bone mineralization. Despite the importance of TMEM16F-mediated phospholipid scrambling in various biological reactions, the fundamental features of the scrambling reaction remain elusive due to technical difficulties in the preparation of a platform for assaying scramblase activity in vitro. Here, we established a method to express and purify mouse TMEM16F as a dimeric molecule by constructing a stable cell line and developed a microarray containing membrane bilayers with asymmetrically distributed phospholipids as a platform for single-molecule scramblase assays. The purified TMEM16F was integrated into the microarray, and monitoring of phospholipid translocation showed that a single TMEM16F molecule transported phospholipids nonspecifically between the membrane bilayers in a Ca2+-dependent manner. Thermodynamic analysis of the reaction indicated that TMEM16F transported 4.5 × 104 lipids per second at 25 °C, with an activation free energy of 47 kJ/mol. These biophysical features were similar to those observed with channels, which transport substrates by facilitating diffusion, and supported the stepping-stone model for the TMEM16F phospholipid scramblase.
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58
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Abstract
The human body generates 10-100 billion cells every day, and the same number of cells die to maintain homeostasis in our body. Cells infected by bacteria or viruses also die. The cell death that occurs under physiological conditions mainly proceeds by apoptosis, which is a noninflammatory, or silent, process, while pathogen infection induces necroptosis or pyroptosis, which activates the immune system and causes inflammation. Dead cells generated by apoptosis are quickly engulfed by macrophages for degradation. Caspases are a large family of cysteine proteases that act in cascades. A cascade that leads to caspase 3 activation mediates apoptosis and is responsible for killing cells, recruiting macrophages, and presenting an "eat me" signal(s). When apoptotic cells are not efficiently engulfed by macrophages, they undergo secondary necrosis and release intracellular materials that represent a damage-associated molecular pattern, which may lead to a systemic lupus-like autoimmune disease.
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Affiliation(s)
- Shigekazu Nagata
- Laboratory of Biochemistry and Immunology, World Premier International Research Center Initiative Immunology Frontier Research Center, Osaka University, Osaka 565-0871, Japan;
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59
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Balla T. Ca 2+ and lipid signals hold hands at endoplasmic reticulum-plasma membrane contact sites. J Physiol 2018; 596:2709-2716. [PMID: 29210464 DOI: 10.1113/jp274957] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 11/17/2017] [Indexed: 12/13/2022] Open
Abstract
Discovery of the STIM1 and Orai proteins as the principal components of store-operated Ca2+ entry has drawn attention to contact sites between the endoplasmic reticulum (ER) and the plasma membrane (PM). Such contacts between adjacent membranes of different cellular organelles, primarily between the mitochondria and the ER, had already been known as the sites where Ca2+ released from the ER can be efficiently channelled to the mitochondria and also where phosphatidylserine synthesis and transfer takes place. Recent studies have identified contact sites between virtually every organelle and the ER and the functional importance of these small specialized membrane domains is increasingly recognized. Most recent developments have highlighted the role of phosphatidylinositol 4-phosphate gradients as critical determinants of the non-vesicular transport of various lipids from the ER to other organelles such as the Golgi or PM. As we learn more about membrane contact sites it becomes apparent that Ca2+ is not only transported at these sites but also controls both the dynamics and the lipid transfer efficiency of these processes. Conversely, lipids are critical for regulating the Ca2+ entry process. This review will summarize some of the most exciting recent developments in this rapidly expanding research field.
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Affiliation(s)
- Tamas Balla
- Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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60
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Verchère A, Ou WL, Ploier B, Morizumi T, Goren MA, Bütikofer P, Ernst OP, Khelashvili G, Menon AK. Light-independent phospholipid scramblase activity of bacteriorhodopsin from Halobacterium salinarum. Sci Rep 2017; 7:9522. [PMID: 28842688 PMCID: PMC5572738 DOI: 10.1038/s41598-017-09835-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 07/31/2017] [Indexed: 12/11/2022] Open
Abstract
The retinylidene protein bacteriorhodopsin (BR) is a heptahelical light-dependent proton pump found in the purple membrane of the archaeon Halobacterium salinarum. We now show that when reconstituted into large unilamellar vesicles, purified BR trimers exhibit light-independent lipid scramblase activity, thereby facilitating transbilayer exchange of phospholipids between the leaflets of the vesicle membrane at a rate >10,000 per trimer per second. This activity is comparable to that of recently described scramblases including bovine rhodopsin and fungal TMEM16 proteins. Specificity tests reveal that BR scrambles fluorescent analogues of common phospholipids but does not transport a glycosylated diphosphate isoprenoid lipid. In silico analyses suggest that membrane-exposed polar residues in transmembrane helices 1 and 2 of BR may provide the molecular basis for lipid translocation by coordinating the polar head-groups of transiting phospholipids. Consistent with this possibility, extensive coarse-grained molecular dynamics simulations of a BR trimer in an explicit phospholipid membrane revealed water penetration along transmembrane helix 1 with the cooperation of a polar residue (Y147 in transmembrane helix 5) in the adjacent protomer. These results suggest that the lipid translocation pathway may lie at or near the interface of the protomers of a BR trimer.
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Affiliation(s)
- Alice Verchère
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York, 10065, USA
| | - Wei-Lin Ou
- Department of Biochemistry, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - Birgit Ploier
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York, 10065, USA
| | - Takefumi Morizumi
- Department of Biochemistry, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - Michael A Goren
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York, 10065, USA
| | - Peter Bütikofer
- Institute of Biochemistry and Molecular Medicine, University of Bern, 3012, Bern, Switzerland
| | - Oliver P Ernst
- Department of Biochemistry, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada, M5S 1A8.,Department of Molecular Genetics, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - George Khelashvili
- Department of Physiology and Biophysics, and Institute for Computational Biomedicine, Weill Cornell Medical College, 1300 York Avenue, New York, New York, 10065, USA
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York, 10065, USA.
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