51
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Tembo M, Wozniak KL, Bainbridge RE, Carlson AE. Phosphatidylinositol 4,5-bisphosphate (PIP 2) and Ca 2+ are both required to open the Cl - channel TMEM16A. J Biol Chem 2019; 294:12556-12564. [PMID: 31266809 DOI: 10.1074/jbc.ra118.007128] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 07/01/2019] [Indexed: 12/27/2022] Open
Abstract
Transmembrane member 16A (TMEM16A) is a widely expressed Ca2+-activated Cl- channel with various physiological functions ranging from mucosal secretion to regulating smooth muscle contraction. Understanding how TMEM16A controls these physiological processes and how its dysregulation may cause disease requires a detailed understanding of how cellular processes and second messengers alter TMEM16A channel gating. Here we assessed the regulation of TMEM16A gating by recording Ca2+-evoked Cl- currents conducted by endogenous TMEM16A channels expressed in Xenopus laevis oocytes, using the inside-out configuration of the patch clamp technique. During continuous application of Ca2+, we found that TMEM16A-conducted currents decay shortly after patch excision. Such current rundown is common among channels regulated by phosphatidylinositol 4,5-bisphosphate (PIP2). Thus, we sought to investigate a possible role of PIP2 in TMEM16A gating. Consistently, synthetic PIP2 rescued the current after rundown, and the application of PIP2 modulating agents altered the speed kinetics of TMEM16A current rundown. First, two PIP2 sequestering agents, neomycin and anti-PIP2, applied to the intracellular surface of excised patches sped up TMEM16A current rundown to nearly twice as fast. Conversely, rephosphorylation of phosphatidylinositol (PI) derivatives into PIP2 using Mg-ATP or inhibiting dephosphorylation of PIP2 using β-glycerophosphate slowed rundown by nearly 3-fold. Our results reveal that TMEM16A regulation is more complicated than it initially appeared; not only is Ca2+ necessary to signal TMEM16a opening, but PIP2 is also required. These findings improve our understanding of how the dysregulation of these pathways may lead to disease and suggest that targeting these pathways could have utility for potential therapies.
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Affiliation(s)
- Maiwase Tembo
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Katherine L Wozniak
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Rachel E Bainbridge
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Anne E Carlson
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260.
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52
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Le T, Jia Z, Le SC, Zhang Y, Chen J, Yang H. An inner activation gate controls TMEM16F phospholipid scrambling. Nat Commun 2019; 10:1846. [PMID: 31015464 PMCID: PMC6478717 DOI: 10.1038/s41467-019-09778-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 03/27/2019] [Indexed: 12/15/2022] Open
Abstract
Transmembrane protein 16F (TMEM16F) is an enigmatic Ca2+-activated phospholipid scramblase (CaPLSase) that passively transports phospholipids down their chemical gradients and mediates blood coagulation, bone development and viral infection. Despite recent advances in the structure and function understanding of TMEM16 proteins, how mammalian TMEM16 CaPLSases open and close, or gate their phospholipid permeation pathways remains unclear. Here we identify an inner activation gate, which is established by three hydrophobic residues, F518, Y563 and I612, in the middle of the phospholipid permeation pathway of TMEM16F-CaPLSase. Disrupting the inner gate profoundly alters TMEM16F phospholipid permeation. Lysine substitutions of F518 and Y563 even lead to constitutively active CaPLSases that bypass Ca2+-dependent activation. Strikingly, an analogous lysine mutation to TMEM16F-F518 in TMEM16A (L543K) is sufficient to confer CaPLSase activity to the Ca2+-activated Cl- channel (CaCC). The identification of an inner activation gate can help elucidate the gating and permeation mechanism of TMEM16 CaPLSases and channels.
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Affiliation(s)
- Trieu Le
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA
| | - Son C Le
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - Yang Zhang
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, 01003, MA, USA
| | - Huanghe Yang
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA.
- Department of Neurobiology, Duke University Medical Center, Durham, 27710, NC, USA.
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53
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Tembo M, Carlson AE. Under pressure: Ano1 mediates pressure sensing in the lymphatic system. J Gen Physiol 2019; 151:404-406. [PMID: 30886053 PMCID: PMC6445580 DOI: 10.1085/jgp.201912320] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Tembo and Carlson reflect on recent work describing a new role for Ano1 in lymphatic collecting vessels.
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Affiliation(s)
- Maiwase Tembo
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA
| | - Anne E Carlson
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA
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54
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Kalienkova V, Clerico Mosina V, Bryner L, Oostergetel GT, Dutzler R, Paulino C. Stepwise activation mechanism of the scramblase nhTMEM16 revealed by cryo-EM. eLife 2019; 8:e44364. [PMID: 30785398 PMCID: PMC6414200 DOI: 10.7554/elife.44364] [Citation(s) in RCA: 77] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Accepted: 02/08/2019] [Indexed: 12/26/2022] Open
Abstract
Scramblases catalyze the movement of lipids between both leaflets of a bilayer. Whereas the X-ray structure of the protein nhTMEM16 has previously revealed the architecture of a Ca2+-dependent lipid scramblase, its regulation mechanism has remained elusive. Here, we have used cryo-electron microscopy and functional assays to address this question. Ca2+-bound and Ca2+-free conformations of nhTMEM16 in detergent and lipid nanodiscs illustrate the interactions with its environment and they reveal the conformational changes underlying its activation. In this process, Ca2+ binding induces a stepwise transition of the catalytic subunit cavity, converting a closed cavity that is shielded from the membrane in the absence of ligand, into a polar furrow that becomes accessible to lipid headgroups in the Ca2+-bound state. Additionally, our structures demonstrate how nhTMEM16 distorts the membrane at both entrances of the subunit cavity, thereby decreasing the energy barrier for lipid movement.
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Affiliation(s)
| | - Vanessa Clerico Mosina
- Department of Structural Biology, Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenThe Netherlands
| | - Laura Bryner
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Gert T Oostergetel
- Department of Structural Biology, Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenThe Netherlands
| | - Raimund Dutzler
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Cristina Paulino
- Department of Structural Biology, Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenThe Netherlands
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55
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Alvadia C, Lim NK, Clerico Mosina V, Oostergetel GT, Dutzler R, Paulino C. Cryo-EM structures and functional characterization of the murine lipid scramblase TMEM16F. eLife 2019; 8:e44365. [PMID: 30785399 PMCID: PMC6414204 DOI: 10.7554/elife.44365] [Citation(s) in RCA: 102] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Accepted: 02/19/2019] [Indexed: 12/13/2022] Open
Abstract
The lipid scramblase TMEM16F initiates blood coagulation by catalyzing the exposure of phosphatidylserine in platelets. The protein is part of a family of membrane proteins, which encompasses calcium-activated channels for ions and lipids. Here, we reveal features of murine TMEM16F (mTMEM16F) that underlie its function as a lipid scramblase and an ion channel. The cryo-EM data of mTMEM16F in absence and presence of Ca2+ define the ligand-free closed conformation of the protein and the structure of a Ca2+-bound intermediate. Both conformations resemble their counterparts of the scrambling-incompetent anion channel mTMEM16A, yet with distinct differences in the region of ion and lipid permeation. In conjunction with functional data, we demonstrate the relationship between ion conduction and lipid scrambling. Although activated by a common mechanism, both functions appear to be mediated by alternate protein conformations that are at equilibrium in the ligand-bound state.
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Affiliation(s)
| | - Novandy K Lim
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Vanessa Clerico Mosina
- Department of Structural Biology at the Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenNetherlands
| | - Gert T Oostergetel
- Department of Structural Biology at the Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenNetherlands
| | - Raimund Dutzler
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Cristina Paulino
- Department of Structural Biology at the Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenGroningenNetherlands
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56
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Han TW, Ye W, Bethel NP, Zubia M, Kim A, Li KH, Burlingame AL, Grabe M, Jan YN, Jan LY. Chemically induced vesiculation as a platform for studying TMEM16F activity. Proc Natl Acad Sci U S A 2019; 116:1309-1318. [PMID: 30622179 PMCID: PMC6347726 DOI: 10.1073/pnas.1817498116] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Calcium-activated phospholipid scramblase mediates the energy-independent bidirectional translocation of lipids across the bilayer, leading to transient or, in the case of apoptotic scrambling, sustained collapse of membrane asymmetry. Cells lacking TMEM16F-dependent lipid scrambling activity are deficient in generation of extracellular vesicles (EVs) that shed from the plasma membrane in a Ca2+-dependent manner, namely microvesicles. We have adapted chemical induction of giant plasma membrane vesicles (GPMVs), which require both TMEM16F-dependent phospholipid scrambling and calcium influx, as a kinetic assay to investigate the mechanism of TMEM16F activity. Using the GPMV assay, we identify and characterize both inactivating and activating mutants that elucidate the mechanism for TMEM16F activation and facilitate further investigation of TMEM16F-mediated lipid translocation and its role in extracellular vesiculation.
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Affiliation(s)
- Tina W Han
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Wenlei Ye
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Neville P Bethel
- Department of Pharmaceutical Chemistry, Cardiovascular Research Institute, University of California, San Francisco, CA 94143
| | - Mario Zubia
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Andrew Kim
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Kathy H Li
- Mass Spectrometry Facility, University of California, San Francisco, CA 94143
| | - Alma L Burlingame
- Mass Spectrometry Facility, University of California, San Francisco, CA 94143
| | - Michael Grabe
- Department of Pharmaceutical Chemistry, Cardiovascular Research Institute, University of California, San Francisco, CA 94143
| | - Yuh Nung Jan
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Lily Y Jan
- Howard Hughes Medical Institute, University of California, San Francisco, CA 94143;
- Department of Physiology, University of California, San Francisco, CA 94143
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
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57
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Falzone ME, Rheinberger J, Lee BC, Peyear T, Sasset L, Raczkowski AM, Eng ET, Di Lorenzo A, Andersen OS, Nimigean CM, Accardi A. Structural basis of Ca 2+-dependent activation and lipid transport by a TMEM16 scramblase. eLife 2019; 8:e43229. [PMID: 30648972 PMCID: PMC6355197 DOI: 10.7554/elife.43229] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 01/02/2019] [Indexed: 12/21/2022] Open
Abstract
The lipid distribution of plasma membranes of eukaryotic cells is asymmetric and phospholipid scramblases disrupt this asymmetry by mediating the rapid, nonselective transport of lipids down their concentration gradients. As a result, phosphatidylserine is exposed to the outer leaflet of membrane, an important step in extracellular signaling networks controlling processes such as apoptosis, blood coagulation, membrane fusion and repair. Several TMEM16 family members have been identified as Ca2+-activated scramblases, but the mechanisms underlying their Ca2+-dependent gating and their effects on the surrounding lipid bilayer remain poorly understood. Here, we describe three high-resolution cryo-electron microscopy structures of a fungal scramblase from Aspergillus fumigatus, afTMEM16, reconstituted in lipid nanodiscs. These structures reveal that Ca2+-dependent activation of the scramblase entails global rearrangement of the transmembrane and cytosolic domains. These structures, together with functional experiments, suggest that activation of the protein thins the membrane near the transport pathway to facilitate rapid transbilayer lipid movement.
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Affiliation(s)
- Maria E Falzone
- Department of BiochemistryWeill Cornell Medical CollegeNew YorkUnited States
| | - Jan Rheinberger
- Department of AnesthesiologyWeill Cornell Medical CollegeNew YorkUnited States
| | - Byoung-Cheol Lee
- Department of AnesthesiologyWeill Cornell Medical CollegeNew YorkUnited States
- Department of Structure and Function on Neural NetworkKorea Brain Research InstituteDeaguRepublic of Korea
| | - Thasin Peyear
- Department of Physiology and BiophysicsWeill Cornell Medical CollegeNew YorkUnited States
| | - Linda Sasset
- Department of PathologyWeill Cornell Medical CollegeNew YorkUnited States
| | - Ashleigh M Raczkowski
- Simons Electron Microscopy CenterNew York Structural Biology CenterNew YorkUnited States
| | - Edward T Eng
- Simons Electron Microscopy CenterNew York Structural Biology CenterNew YorkUnited States
| | | | - Olaf S Andersen
- Department of Physiology and BiophysicsWeill Cornell Medical CollegeNew YorkUnited States
| | - Crina M Nimigean
- Department of BiochemistryWeill Cornell Medical CollegeNew YorkUnited States
- Department of AnesthesiologyWeill Cornell Medical CollegeNew YorkUnited States
- Department of Physiology and BiophysicsWeill Cornell Medical CollegeNew YorkUnited States
| | - Alessio Accardi
- Department of BiochemistryWeill Cornell Medical CollegeNew YorkUnited States
- Department of AnesthesiologyWeill Cornell Medical CollegeNew YorkUnited States
- Department of Physiology and BiophysicsWeill Cornell Medical CollegeNew YorkUnited States
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58
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Lam AK, Dutzler R. Calcium-dependent electrostatic control of anion access to the pore of the calcium-activated chloride channel TMEM16A. eLife 2018; 7:39122. [PMID: 30311910 PMCID: PMC6195346 DOI: 10.7554/elife.39122] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 10/11/2018] [Indexed: 12/14/2022] Open
Abstract
TMEM16A is a ligand-gated anion channel that is activated by intracellular Ca2+. This channel comprises two independent pores and closely apposed Ca2+ binding sites that are contained within each subunit of a homodimeric protein. Previously we characterized the influence of positively charged pore-lining residues on anion conduction (Paulino et al., 2017a). Here, we demonstrate the electrostatic control of permeation by the bound calcium ions in mouse TMEM16A using electrophysiology and Poisson-Boltzmann calculations. The currents of constitutively active mutants lose their outward rectification as a function of Ca2+ concentration due to the alleviation of energy barriers for anion conduction. This phenomenon originates from Coulombic interactions between the bound Ca2+ and permeating anions and thus demonstrates that an electrostatic gate imposed by the vacant binding site present in the sterically open pore, is released by Ca2+ binding to enable an otherwise sub-conductive pore to conduct with full capacity.
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Affiliation(s)
- Andy Km Lam
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Raimund Dutzler
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
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59
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Ballesteros A, Fenollar-Ferrer C, Swartz KJ. Structural relationship between the putative hair cell mechanotransduction channel TMC1 and TMEM16 proteins. eLife 2018; 7:38433. [PMID: 30063209 PMCID: PMC6067890 DOI: 10.7554/elife.38433] [Citation(s) in RCA: 76] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 07/09/2018] [Indexed: 02/03/2023] Open
Abstract
The hair cell mechanotransduction (MET) channel complex is essential for hearing, yet it's molecular identity and structure remain elusive. The transmembrane channel-like 1 (TMC1) protein localizes to the site of the MET channel, interacts with the tip-link responsible for mechanical gating, and genetic alterations in TMC1 alter MET channel properties and cause deafness, supporting the hypothesis that TMC1 forms the MET channel. We generated a model of TMC1 based on X-ray and cryo-EM structures of TMEM16 proteins, revealing the presence of a large cavity near the protein-lipid interface that also harbors the Beethoven mutation, suggesting that it could function as a permeation pathway. We also find that hair cells are permeable to 3 kDa dextrans, and that dextran permeation requires TMC1/2 proteins and functional MET channels, supporting the presence of a large permeation pathway and the hypothesis that TMC1 is a pore forming subunit of the MET channel complex.
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Affiliation(s)
- Angela Ballesteros
- Molecular Physiology and Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Cristina Fenollar-Ferrer
- Laboratory of Molecular & Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States.,Laboratory of Molecular Genetics, National Institute of Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, United States.,Molecular Biology and Genetics Section, National Institute of Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, United States
| | - Kenton Jon Swartz
- Molecular Physiology and Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
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60
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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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61
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Cryo-EM structures of the TMEM16A calcium-activated chloride channel. Nature 2017; 552:426-429. [PMID: 29236684 PMCID: PMC5750132 DOI: 10.1038/nature25024] [Citation(s) in RCA: 224] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Accepted: 11/10/2017] [Indexed: 12/19/2022]
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