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Arreola J, López-Romero AE, Huerta M, Guzmán-Hernández ML, Pérez-Cornejo P. Insights into the function and regulation of the calcium-activated chloride channel TMEM16A. Cell Calcium 2024; 121:102891. [PMID: 38772195 DOI: 10.1016/j.ceca.2024.102891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/23/2024] [Accepted: 04/23/2024] [Indexed: 05/23/2024]
Abstract
The TMEM16A channel, a member of the TMEM16 protein family comprising chloride (Cl-) channels and lipid scramblases, is activated by the free intracellular Ca2+ increments produced by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release after GqPCRs or Ca2+ entry through cationic channels. It is a ubiquitous transmembrane protein that participates in multiple physiological functions essential to mammals' lives. TMEM16A structure contains two identical 10-segment monomers joined at their transmembrane segment 10. Each monomer harbours one independent hourglass-shaped pore gated by Ca2+ ligation to an orthosteric site adjacent to the pore and controlled by two gates. The orthosteric site is created by assembling negatively charged glutamate side chains near the pore´s cytosolic end. When empty, this site generates an electrostatic barrier that controls channel rectification. In addition, an isoleucine-triad forms a hydrophobic gate at the boundary of the cytosolic vestibule and the inner side of the neck. When the cytosolic Ca2+ rises, one or two Ca2+ ions bind to the orthosteric site in a voltage (V)-dependent manner, thus neutralising the electrostatic barrier and triggering an allosteric gating mechanism propagating via transmembrane segment 6 to the hydrophobic gate. These coordinated events lead to pore opening, allowing the Cl- flux to ensure the physiological response. The Ca2+-dependent function of TMEM16A is highly regulated. Anions with higher permeability than Cl- facilitate V dependence by increasing the Ca2+ sensitivity, intracellular protons can replace Ca2+ and induce channel opening, and phosphatidylinositol 4,5-bisphosphate bound to four cytosolic sites likely maintains Ca2+ sensitivity. Additional regulation is afforded by cytosolic proteins, most likely by phosphorylation and protein-protein interaction mechanisms.
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Affiliation(s)
- Jorge Arreola
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico.
| | - Ana Elena López-Romero
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - Miriam Huerta
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - María Luisa Guzmán-Hernández
- Catedrática CONAHCYT, Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
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Dibattista M, Pifferi S, Hernandez-Clavijo A, Menini A. The physiological roles of anoctamin2/TMEM16B and anoctamin1/TMEM16A in chemical senses. Cell Calcium 2024; 120:102889. [PMID: 38677213 DOI: 10.1016/j.ceca.2024.102889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/11/2024] [Accepted: 04/17/2024] [Indexed: 04/29/2024]
Abstract
Chemical senses allow animals to detect and discriminate a vast array of molecules. The olfactory system is responsible of the detection of small volatile molecules, while water dissolved molecules are detected by taste buds in the oral cavity. Moreover, many animals respond to signaling molecules such as pheromones and other semiochemicals through the vomeronasal organ. The peripheral organs dedicated to chemical detection convert chemical signals into perceivable information through the employment of diverse receptor types and the activation of multiple ion channels. Two ion channels, TMEM16B, also known as anoctamin2 (ANO2) and TMEM16A, or anoctamin1 (ANO1), encoding for Ca2+-activated Cl¯ channels, have been recently described playing critical roles in various cell types. This review aims to discuss the main properties of TMEM16A and TMEM16B-mediated currents and their physiological roles in chemical senses. In olfactory sensory neurons, TMEM16B contributes to amplify the odorant response, to modulate firing, response kinetics and adaptation. TMEM16A and TMEM16B shape the pattern of action potentials in vomeronasal sensory neurons increasing the interspike interval. In type I taste bud cells, TMEM16A is activated during paracrine signaling mediated by ATP. This review aims to shed light on the regulation of diverse signaling mechanisms and neuronal excitability mediated by Ca-activated Cl¯ channels, hinting at potential new roles for TMEM16A and TMEM16B in the chemical senses.
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Affiliation(s)
- Michele Dibattista
- Department of Translational Biomedicine and Neuroscience, University of Bari A. Moro, 70121 Bari, Italy
| | - Simone Pifferi
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, 60126 Ancona, Italy.
| | - Andres Hernandez-Clavijo
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, 52074 Aachen, Germany
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy.
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3
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Arreola J, Pérez-Cornejo P, Segura-Covarrubias G, Corral-Fernández N, León-Aparicio D, Guzmán-Hernández ML. Function and Regulation of the Calcium-Activated Chloride Channel Anoctamin 1 (TMEM16A). Handb Exp Pharmacol 2024; 283:101-151. [PMID: 35768554 DOI: 10.1007/164_2022_592] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Various human tissues express the calcium-activated chloride channel Anoctamin 1 (ANO1), also known as TMEM16A. ANO1 allows the passive chloride flux that controls different physiological functions ranging from muscle contraction, fluid and hormone secretion, gastrointestinal motility, and electrical excitability. Overexpression of ANO1 is associated with pathological conditions such as hypertension and cancer. The molecular cloning of ANO1 has led to a surge in structural, functional, and physiological studies of the channel in several tissues. ANO1 is a homodimer channel harboring two pores - one in each monomer - that work independently. Each pore is activated by voltage-dependent binding of two intracellular calcium ions to a high-affinity-binding site. In addition, the binding of phosphatidylinositol 4,5-bisphosphate to sites scattered throughout the cytosolic side of the protein aids the calcium activation process. Furthermore, many pharmacological studies have established ANO1 as a target of promising compounds that could treat several illnesses. This chapter describes our current understanding of the physiological roles of ANO1 and its regulation under physiological conditions as well as new pharmacological compounds with potential therapeutic applications.
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Affiliation(s)
- Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico.
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, School of Medicine of Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
| | - Guadalupe Segura-Covarrubias
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, USA
| | - Nancy Corral-Fernández
- Department of Physiology and Biophysics, School of Medicine of Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
| | - Daniel León-Aparicio
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
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4
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Nguyen DM, Chen TY. Structure and Function of Calcium-Activated Chloride Channels and Phospholipid Scramblases in the TMEM16 Family. Handb Exp Pharmacol 2024; 283:153-180. [PMID: 35792944 DOI: 10.1007/164_2022_595] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated chloride channels and phospholipid scramblases. Ten mammalian TMEM16 proteins, TMEM16A-K (with no TMEM16I), and several non-mammalian TMEM16 proteins, such as afTMEM16 and nhTMEM16, have been discovered. All known TMEM16 proteins are homodimeric proteins containing two subunits. Each subunit consists of ten transmembrane helices with Ca2+-binding sites and a single ion-permeation/phospholipid transport pathway. The ion-permeation pathway and the phospholipid transport pathway of TMEM16 proteins have a wide intracellular vestibule, a narrow neck, and a smaller extracellular vestibule. Interestingly, the lining wall of the ion-permeation/phospholipid transport pathway may be formed, at least partially, by membrane phospholipids, though the degree of pore-wall forming by phospholipids likely varies among TMEM16 proteins. Thus, the biophysical properties and activation mechanisms of TMEM16 proteins could differ from each other accordingly. Here we review the current understanding of the structure and function of TMEM16 molecules.
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Affiliation(s)
- Dung Manh Nguyen
- Center for Neuroscience, University of California, Davis, CA, USA.
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA.
| | - Tsung-Yu Chen
- Department of Neurology, Center for Neuroscience, University of California, Davis, CA, USA.
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5
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Guo S, Zhang L, Li N. ANO1: More Than Just Calcium-Activated Chloride Channel in Cancer. Front Oncol 2022; 12:922838. [PMID: 35734591 PMCID: PMC9207239 DOI: 10.3389/fonc.2022.922838] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 05/09/2022] [Indexed: 11/22/2022] Open
Abstract
ANO1, a calcium-activated chloride channel (CACC), is also known as transmembrane protein 16A (TMEM16A). It plays a vital role in the occurrence, development, metastasis, proliferation, and apoptosis of various malignant tumors. This article reviews the mechanism of ANO1 involved in the replication, proliferation, invasion and apoptosis of various malignant tumors. Various molecules and Stimuli control the expression of ANO1, and the regulatory mechanism of ANO1 is different in tumor cells. To explore the mechanism of ANO1 overexpression and activation of tumor cells by studying the different effects of ANO1. Current studies have shown that ANO1 expression is controlled by 11q13 gene amplification and may also exert cell-specific effects through its interconnected protein network, phosphorylation of different kinases, and signaling pathways. At the same time, ANO1 also resists tumor apoptosis and promotes tumor immune escape. ANO1 can be used as a promising biomarker for detecting certain malignant tumors. Further studies on the channels and the mechanism of protein activity of ANO1 are needed. Finally, the latest inhibitors of ANO1 are summarized, which provides the research direction for the tumor-promoting mechanism of ANO1.
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Affiliation(s)
- Saisai Guo
- Department of Oncology, The Second Affiliated Hospital of Dalian Medical University, Dalian, China
| | - Linna Zhang
- Department of Oncology, The Second Affiliated Hospital of Dalian Medical University, Dalian, China
| | - Na Li
- Department of Oncology, The Second Affiliated Hospital of Dalian Medical University, Dalian, China
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6
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De Jesús-Pérez JJ, López-Romero AE, Posadas O, Segura-Covarrubias G, Aréchiga-Figueroa I, Gutiérrez-Medina B, Pérez-Cornejo P, Arreola J. Gating and anion selectivity are reciprocally regulated in TMEM16A (ANO1). J Gen Physiol 2022; 154:213275. [PMID: 35687042 PMCID: PMC9194859 DOI: 10.1085/jgp.202113027] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 05/23/2022] [Indexed: 02/03/2023] Open
Abstract
Numerous essential physiological processes depend on the TMEM16A-mediated Ca2+-activated chloride fluxes. Extensive structure-function studies have helped to elucidate the Ca2+ gating mechanism of TMEM16A, revealing a Ca2+-sensing element close to the anion pore that alters conduction. However, substrate selection and the substrate-gating relationship in TMEM16A remain less explored. Here, we study the gating-permeant anion relationship on mouse TMEM16A expressed in HEK 293 cells using electrophysiological recordings coupled with site-directed mutagenesis. We show that the apparent Ca2+ sensitivity of TMEM16A increased with highly permeant anions and SCN- mole fractions, likely by stabilizing bound Ca2+. Conversely, mutations at crucial gating elements, including the Ca2+-binding site 1, the transmembrane helix 6 (TM6), and the hydrophobic gate, impaired the anion permeability and selectivity of TMEM16A. Finally, we found that, unlike anion-selective wild-type channels, the voltage dependence of unselective TMEM16A mutant channels was less sensitive to SCN-. Therefore, our work identifies structural determinants of selectivity at the Ca2+ site, TM6, and hydrophobic gate and reveals a reciprocal regulation of gating and selectivity. We suggest that this regulation is essential to set ionic selectivity and the Ca2+ and voltage sensitivities in TMEM16A.
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Affiliation(s)
| | - Ana E. López-Romero
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Odalys Posadas
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | | | - Iván Aréchiga-Figueroa
- Consejo Nacional de Ciencia y Tecnología, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Braulio Gutiérrez-Medina
- Advanced Materials Division, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, México
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México,Correspondence to Jorge Arreola:
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7
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Polymodal Control of TMEM16x Channels and Scramblases. Int J Mol Sci 2022; 23:ijms23031580. [PMID: 35163502 PMCID: PMC8835819 DOI: 10.3390/ijms23031580] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2021] [Revised: 01/20/2022] [Accepted: 01/20/2022] [Indexed: 02/01/2023] Open
Abstract
The TMEM16A/anoctamin-1 calcium-activated chloride channel (CaCC) contributes to a range of vital functions, such as the control of vascular tone and epithelial ion transport. The channel is a founding member of a family of 10 proteins (TMEM16x) with varied functions; some members (i.e., TMEM16A and TMEM16B) serve as CaCCs, while others are lipid scramblases, combine channel and scramblase function, or perform additional cellular roles. TMEM16x proteins are typically activated by agonist-induced Ca2+ release evoked by Gq-protein-coupled receptor (GqPCR) activation; thus, TMEM16x proteins link Ca2+-signalling with cell electrical activity and/or lipid transport. Recent studies demonstrate that a range of other cellular factors—including plasmalemmal lipids, pH, hypoxia, ATP and auxiliary proteins—also control the activity of the TMEM16A channel and its paralogues, suggesting that the TMEM16x proteins are effectively polymodal sensors of cellular homeostasis. Here, we review the molecular pathophysiology, structural biology, and mechanisms of regulation of TMEM16x proteins by multiple cellular factors.
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8
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Boccaccio A, Picco C, Di Zanni E, Scholz-Starke J. Phospholipid scrambling by a TMEM16 homolog of Arabidopsis thaliana. FEBS J 2021; 289:2578-2592. [PMID: 34775680 PMCID: PMC9299152 DOI: 10.1111/febs.16279] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 09/15/2021] [Accepted: 11/12/2021] [Indexed: 12/20/2022]
Abstract
Membrane asymmetry is important for cellular physiology and established by energy‐dependent unidirectional lipid translocases, which have diverse physiological functions in plants. By contrast, the role of phospholipid scrambling (PLS), the passive bidirectional lipid transfer leading to the break‐down of membrane asymmetry, is currently still unexplored. The Arabidopsis thaliana genome contains a single gene (At1g73020) with homology to the eukaryotic TMEM16 family of Ca2+‐activated phospholipid scramblases. Here, we investigated the protein function of this Arabidopsis homolog. Fluorescent AtTMEM16 fusions localized to the ER both in transiently expressing Arabidopsis protoplasts and HEK293 cells. A putative scrambling domain (SCRD) was identified on the basis of sequence conservation and conferred PLS to transfected HEK293 cells, when grafted into the backbone of the non‐scrambling plasma membrane‐localized TMEM16A chloride channel. Finally, AtTMEM16 ‘gain‐of‐function’ variants gave rise to cellular phenotypes typical of aberrant scramblase activity, which were reversed by the additional introduction of a ‘loss‐of‐function’ mutation into the SCRD. In conclusion, our data suggest AtTMEM16 works as an ER‐resident lipid scramblase in Arabidopsis.
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Affiliation(s)
- Anna Boccaccio
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Cristiana Picco
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Eleonora Di Zanni
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
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9
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Anion and Cation Permeability of the Mouse TMEM16F Calcium-Activated Channel. Int J Mol Sci 2021; 22:ijms22168578. [PMID: 34445284 PMCID: PMC8395294 DOI: 10.3390/ijms22168578] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 07/31/2021] [Accepted: 08/04/2021] [Indexed: 12/27/2022] Open
Abstract
TMEM16F is involved in several physiological processes, such as blood coagulation, bone development and virus infections. This protein acts both as a Ca2+-dependent phospholipid scramblase and a Ca2+-activated ion channel but several studies have reported conflicting results about the ion selectivity of the TMEM16F-mediated current. Here, we have performed a detailed side-by-side comparison of the ion selectivity of TMEM16F using the whole-cell and inside-out excised patch configurations to directly compare the results. In inside-out configuration, Ca2+-dependent activation was fast and the TMEM16F-mediated current was activated in a few milliseconds, while in whole-cell recordings full activation required several minutes. We determined the relative permeability between Na+ and Cl¯ (PNa/PCl) using the dilution method in both configurations. The TMEM16F-mediated current was highly nonselective, but there were differences depending on the configuration of the recordings. In whole-cell recordings, PNa/PCl was approximately 0.5, indicating a slight preference for Cl¯ permeation. In contrast, in inside-out experiments the TMEM16F channel showed a higher permeability for Na+ with PNa/PCl reaching 3.7. Our results demonstrate that the time dependence of Ca2+ activation and the ion selectivity of TMEM16F depend on the recording configuration.
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10
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The Groovy TMEM16 Family: Molecular Mechanisms of Lipid Scrambling and Ion Conduction. J Mol Biol 2021; 433:166941. [PMID: 33741412 DOI: 10.1016/j.jmb.2021.166941] [Citation(s) in RCA: 52] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 03/09/2021] [Accepted: 03/09/2021] [Indexed: 12/28/2022]
Abstract
The TMEM16 family of membrane proteins displays a remarkable functional dichotomy - while some family members function as Ca2+-activated anion channels, the majority of characterized TMEM16 homologs are Ca2+-activated lipid scramblases, which catalyze the exchange of phospholipids between the two membrane leaflets. Furthermore, some TMEM16 scramblases can also function as channels. Due to their involvement in important physiological processes, the family has been actively studied ever since their molecular identity was unraveled. In this review, we will summarize the recent advances in the field and how they influenced our view of TMEM16 family function and evolution. Structural, functional and computational studies reveal how relatively small rearrangements in the permeation pathway are responsible for the observed functional duality: while TMEM16 scramblases can adopt both ion- and lipid conductive conformations, TMEM16 channels can only populate the former. Recent data further provides the molecular details of a stepwise activation mechanism, which is initiated by Ca2+ binding and modulated by various cellular factors, including lipids. TMEM16 function and the surrounding membrane properties are inextricably intertwined, with the protein inducing bilayer deformations associated with scrambling, while the surrounding lipids modulate TMEM16 conformation and activity.
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11
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Henriques T, Agostinelli E, Hernandez-Clavijo A, Maurya DK, Rock JR, Harfe BD, Menini A, Pifferi S. TMEM16A calcium-activated chloride currents in supporting cells of the mouse olfactory epithelium. J Gen Physiol 2019; 151:954-966. [PMID: 31048412 PMCID: PMC6605691 DOI: 10.1085/jgp.201812310] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 03/08/2019] [Accepted: 04/15/2019] [Indexed: 12/15/2022] Open
Abstract
Glial-like supporting (or sustentacular) cells are important constituents of the olfactory epithelium that are involved in several physiological processes such as production of endocannabinoids, insulin, and ATP and regulation of the ionic composition of the mucus layer that covers the apical surface of the olfactory epithelium. Supporting cells express metabotropic P2Y purinergic receptors that generate ATP-induced Ca2+ signaling through the activation of a PLC-mediated cascade. Recently, we reported that a subpopulation of supporting cells expresses also the Ca2+-activated Cl- channel TMEM16A. Here, we sought to extend our understanding of a possible physiological role of this channel in the olfactory system by asking whether Ca2+ can activate Cl- currents mediated by TMEM16A. We use whole-cell patch-clamp analysis in slices of the olfactory epithelium to measure dose-response relations in the presence of various intracellular Ca2+ concentrations, ion selectivity, and blockage. We find that knockout of TMEM16A abolishes Ca2+-activated Cl- currents, demonstrating that TMEM16A is essential for these currents in supporting cells. Also, by using extracellular ATP as physiological stimuli, we found that the stimulation of purinergic receptors activates a large TMEM16A-dependent Cl- current, indicating a possible role of TMEM16A in ATP-mediated signaling. Altogether, our results establish that TMEM16A-mediated currents are functional in olfactory supporting cells and provide a foundation for future work investigating the precise physiological role of TMEM16A in the olfactory system.
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Affiliation(s)
- Tiago Henriques
- Neurobiology Group, International School for Advanced Studies, Trieste, Italy
| | - Emilio Agostinelli
- Neurobiology Group, International School for Advanced Studies, Trieste, Italy
| | | | | | - Jason R Rock
- Center for Regenerative Medicine, Boston University School of Medicine, Boston, MA
| | - Brian D Harfe
- Department of Molecular Genetics and Microbiology Genetics Institute, University of Florida, College of Medicine, Gainesville, FL
| | - Anna Menini
- Neurobiology Group, International School for Advanced Studies, Trieste, Italy
| | - Simone Pifferi
- Neurobiology Group, International School for Advanced Studies, Trieste, Italy
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12
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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: 35] [Impact Index Per Article: 5.8] [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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13
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Cao X, Pattnaik BR, Hughes BA. Mouse retinal pigment epithelial cells exhibit a thiocyanate-selective conductance. Am J Physiol Cell Physiol 2018; 315:C457-C473. [PMID: 29874109 DOI: 10.1152/ajpcell.00231.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The basolateral membrane anion conductance of the retinal pigment epithelium (RPE) is a key component of the transepithelial Cl- transport pathway. Although multiple Cl- channels have been found to be expressed in the RPE, the components of the resting Cl- conductance have not been identified. In this study, we used the patch-clamp method to characterize the ion selectivity of the anion conductance in isolated mouse RPE cells and in excised patches of RPE basolateral and apical membranes. Relative permeabilities ( PA/ PCl) calculated from reversal potentials measured in intact cells under bi-ionic conditions were as follows: SCN- >> ClO4- > [Formula: see text] > I- > Br- > Cl- >> gluconate. Relative conductances ( GA/ GCl) followed a similar trend of SCN- >> ClO4- > [Formula: see text] > I- > Br- ≈Cl- >> gluconate. Whole cell currents were highly time-dependent in 10 mM external SCN-, reflecting collapse of the electrochemical potential gradient due to SCN- accumulation or depletion intracellularly. When the membrane potential was held at -120 mV to minimize SCN- accumulation in cells exposed to 10 mM SCN-, the instantaneous current reversed at -90 mV, revealing that PSCN/ PCl is approximately 500. Macroscopic current recordings from outside-out patches demonstrated that both the basolateral and apical membranes exhibit SCN- conductances, with the basolateral membrane having a larger SCN- current density and higher relative permeability for SCN-. Our results suggest that the RPE basolateral and apical membranes contain previously unappreciated anion channels or electrogenic transporters that may mediate the transmembrane fluxes of SCN- and Cl-.
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Affiliation(s)
- Xu Cao
- Department of Ophthalmology and Visual Sciences, University of Michigan , Ann Arbor, Michigan
| | - Bikash R Pattnaik
- Department of Ophthalmology and Visual Sciences, University of Michigan , Ann Arbor, Michigan
| | - Bret A Hughes
- Department of Ophthalmology and Visual Sciences, University of Michigan , Ann Arbor, Michigan.,Department of Molecular and Integrative Physiology, University of Michigan , Ann Arbor, Michigan
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14
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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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15
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Medrano-Soto A, Moreno-Hagelsieb G, McLaughlin D, Ye ZS, Hendargo KJ, Saier MH. Bioinformatic characterization of the Anoctamin Superfamily of Ca2+-activated ion channels and lipid scramblases. PLoS One 2018; 13:e0192851. [PMID: 29579047 PMCID: PMC5868767 DOI: 10.1371/journal.pone.0192851] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 01/31/2018] [Indexed: 01/01/2023] Open
Abstract
Our laboratory has developed bioinformatic strategies for identifying distant phylogenetic relationships and characterizing families and superfamilies of transport proteins. Results using these tools suggest that the Anoctamin Superfamily of cation and anion channels, as well as lipid scramblases, includes three functionally characterized families: the Anoctamin (ANO), Transmembrane Channel (TMC) and Ca2+-permeable Stress-gated Cation Channel (CSC) families; as well as four families of functionally uncharacterized proteins, which we refer to as the Anoctamin-like (ANO-L), Transmembrane Channel-like (TMC-L), and CSC-like (CSC-L1 and CSC-L2) families. We have constructed protein clusters and trees showing the relative relationships among the seven families. Topological analyses suggest that the members of these families have essentially the same topologies. Comparative examination of these homologous families provides insight into possible mechanisms of action, indicates the currently recognized organismal distributions of these proteins, and suggests drug design potential for the disease-related channel proteins.
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Affiliation(s)
- Arturo Medrano-Soto
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America
| | | | - Daniel McLaughlin
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America
| | - Zachary S. Ye
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America
| | - Kevin J. Hendargo
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America
| | - Milton H. Saier
- Department of Molecular Biology, University of California at San Diego, La Jolla, California, United States of America
- * E-mail:
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16
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Phosphatidylinositol 4,5-bisphosphate, cholesterol, and fatty acids modulate the calcium-activated chloride channel TMEM16A (ANO1). Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1863:299-312. [PMID: 29277655 DOI: 10.1016/j.bbalip.2017.12.009] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 12/10/2017] [Accepted: 12/18/2017] [Indexed: 11/20/2022]
Abstract
The TMEM16A-mediated Ca2+-activated Cl- current drives several important physiological functions. Membrane lipids regulate ion channels and transporters but their influence on members of the TMEM16 family is poorly understood. Here we have studied the regulation of TMEM16A by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), cholesterol, and fatty acids using patch clamp, biochemistry and fluorescence microscopy. We found that depletion of membrane PI(4,5)P2 causes a decline in TMEM16A current that is independent of cytoskeleton, but is partially prevented by removing intracellular Ca2+. On the other hand, supplying PI(4,5)P2 to inside-out patches attenuated channel rundown and/or partially rescued activity after channel rundown. Also, depletion (with methyl-β-cyclodextrin M-βCD) or restoration (with M-βCD+cholesterol) of membrane cholesterol slows down the current decay observed after reduction of PI(4,5)P2. Neither depletion nor restoration of cholesterol change PI(4,5)P2 content. However, M-βCD alone transiently increases TMEM16A activity and dampens rundown whereas M-βCD+cholesterol increases channel rundown. Thus, PI(4,5)P2 is required for TMEM16A function while cholesterol directly and indirectly via a PI(4,5)P2-independent mechanism regulate channel function. Stearic, arachidonic, oleic, docosahexaenoic, and eicosapentaenoic fatty acids as well as methyl stearate inhibit TMEM16A in a dose- and voltage-dependent manner. Phosphatidylserine, a phospholipid whose hydrocarbon tails contain stearic and oleic acids also inhibits TMEM16A. Finally, we show that TMEM16A remains in the plasma membrane after treatment with M-βCD, M-βCD+cholesterol, oleic, or docosahexaenoic acids. Thus, we propose that lipids and fatty acids regulate TMEM16A channels through a membrane-delimited protein-lipid interaction.
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17
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Activation mechanism of the calcium-activated chloride channel TMEM16A revealed by cryo-EM. Nature 2017; 552:421-425. [PMID: 29236691 DOI: 10.1038/nature24652] [Citation(s) in RCA: 198] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 10/18/2017] [Indexed: 12/21/2022]
Abstract
The calcium-activated chloride channel TMEM16A is a ligand-gated anion channel that opens in response to an increase in intracellular Ca2+ concentration. The protein is broadly expressed and contributes to diverse physiological processes, including transepithelial chloride transport and the control of electrical signalling in smooth muscles and certain neurons. As a member of the TMEM16 (or anoctamin) family of membrane proteins, TMEM16A is closely related to paralogues that function as scramblases, which facilitate the bidirectional movement of lipids across membranes. The unusual functional diversity of the TMEM16 family and the relationship between two seemingly incompatible transport mechanisms has been the focus of recent investigations. Previous breakthroughs were obtained from the X-ray structure of the lipid scramblase of the fungus Nectria haematococca (nhTMEM16), and from the cryo-electron microscopy structure of mouse TMEM16A at 6.6 Å (ref. 14). Although the latter structure disclosed the architectural differences that distinguish ion channels from lipid scramblases, its low resolution did not permit a detailed molecular description of the protein or provide any insight into its activation by Ca2+. Here we describe the structures of mouse TMEM16A at high resolution in the presence and absence of Ca2+. These structures reveal the differences between ligand-bound and ligand-free states of a calcium-activated chloride channel, and when combined with functional experiments suggest a mechanism for gating. During activation, the binding of Ca2+ to a site located within the transmembrane domain, in the vicinity of the pore, alters the electrostatic properties of the ion conduction path and triggers a conformational rearrangement of an α-helix that comes into physical contact with the bound ligand, and thereby directly couples ligand binding and pore opening. Our study describes a process that is unique among channel proteins, but one that is presumably general for both functional branches of the TMEM16 family.
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18
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Abstract
JGP hosts key papers that shaped the epithelial transport field. Epithelia define the boundaries of the body and often transfer solutes and water from outside to inside (absorption) or from inside to outside (secretion). Those processes involve dual plasma membranes with different transport components that interact with each other. Understanding those functions has entailed breaking down the problem to analyze properties of individual membranes (apical vs. basolateral) and individual transport proteins. It also requires understanding of how those components interact and how they are regulated. This article outlines the modern history of this research as reflected by publications in The Journal of General Physiology.
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Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, NY
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19
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Ta CM, Acheson KE, Rorsman NJG, Jongkind RC, Tammaro P. Contrasting effects of phosphatidylinositol 4,5-bisphosphate on cloned TMEM16A and TMEM16B channels. Br J Pharmacol 2017; 174:2984-2999. [PMID: 28616863 PMCID: PMC5573538 DOI: 10.1111/bph.13913] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 06/09/2017] [Accepted: 06/10/2017] [Indexed: 12/19/2022] Open
Abstract
Background and Purpose Ca2+‐activated Cl− channels (CaCCs) are gated open by a rise in intracellular Ca2+ concentration ([Ca2+]i), typically provoked by activation of Gq‐protein coupled receptors (GqPCR). GqPCR activation initiates depletion of plasmalemmal phosphatidylinositol 4,5‐bisphosphate (PIP2). Here, we determined whether PIP2 acts as a signalling lipid for CaCCs coded by the TMEM16A and TMEM16B genes. Experimental Approach Patch‐clamp electrophysiology, in conjunction with genetically encoded systems to control cellular PIP2 content, was used to define the mechanism of action of PIP2 on TMEM16A and TMEM16B channels. Key Results A water‐soluble PIP2 analogue (diC8‐PIP2) activated TMEM16A channels by up to fivefold and inhibited TMEM16B by ~0.2‐fold. The effects of diC8‐PIP2 on TMEM16A currents were especially pronounced at low [Ca2+]i. In contrast, diC8‐PIP2 modulation of TMEM16B channels did not vary over a broad [Ca2+]i range but was only detectable at highly depolarized membrane potentials. Modulation of TMEM16A and TMEM16B currents was due to changes in channel gating, while single channel conductance was unaltered. Co‐expression of TMEM16A or TMEM16B with a Danio rerio voltage‐sensitive phosphatase (DrVSP), which degrades PIP2, led to reduction and enhancement of TMEM16A and TMEM16B currents respectively. These effects were abolished by an inactivating mutation in DrVSP and antagonized by simultaneous co‐expression of a phosphatidylinositol‐4‐phosphate 5‐kinase that catalyses PIP2 formation. Conclusions and Implications PIP2 acts as a modifier of TMEM16A and TMEM16B channel gating. Drugs interacting with PIP2 signalling may affect TMEM16A and TMEM16B channel gating and have potential uses in basic science and implications for therapy.
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Affiliation(s)
- Chau M Ta
- Department of Pharmacology, University of Oxford, Oxford, UK
| | | | - Nils J G Rorsman
- Department of Pharmacology, University of Oxford, Oxford, UK.,OXION Wellcome Trust Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | | | - Paolo Tammaro
- Department of Pharmacology, University of Oxford, Oxford, UK.,OXION Wellcome Trust Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
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20
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Kamaleddin MA. Molecular, biophysical, and pharmacological properties of calcium-activated chloride channels. J Cell Physiol 2017; 233:787-798. [PMID: 28121009 DOI: 10.1002/jcp.25823] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 01/24/2017] [Indexed: 12/15/2022]
Abstract
Calcium-activated chloride channels (CaCCs) are a family of anionic transmembrane ion channels. They are mainly responsible for the movement of Cl- and other anions across the biological membranes, and they are widely expressed in different tissues. Since the Cl- flow into or out of the cell plays a crucial role in hyperpolarizing or depolarizing the cells, respectively, the impact of intracellular Ca2+ concentration on these channels is attracting a lot of attentions. After summarizing the molecular, biophysical, and pharmacological properties of CaCCs, the role of CaCCs in normal cellular functions will be discussed, and I will emphasize how dysregulation of CaCCs in pathological conditions can account for different diseases. A better understanding of CaCCs and a pivotal regulatory role of Ca2+ can shed more light on the therapeutic strategies for different neurological disorders that arise from chloride dysregulation, such as asthma, cystic fibrosis, and neuropathic pain.
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Affiliation(s)
- Mohammad Amin Kamaleddin
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.,Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
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21
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Pifferi S. Permeation Mechanisms in the TMEM16B Calcium-Activated Chloride Channels. PLoS One 2017; 12:e0169572. [PMID: 28046119 PMCID: PMC5207786 DOI: 10.1371/journal.pone.0169572] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Accepted: 12/18/2016] [Indexed: 12/03/2022] Open
Abstract
TMEM16A and TMEM16B encode for Ca2+-activated Cl− channels (CaCC) and are expressed in many cell types and play a relevant role in many physiological processes. Here, I performed a site-directed mutagenesis study to understand the molecular mechanisms of ion permeation of TMEM16B. I mutated two positive charged residues R573 and K540, respectively located at the entrance and inside the putative channel pore and I measured the properties of wild-type and mutant TMEM16B channels expressed in HEK-293 cells using whole-cell and excised inside-out patch clamp experiments. I found evidence that R573 and K540 control the ion permeability of TMEM16B depending both on which side of the membrane the ion substitution occurs and on the level of channel activation. Moreover, these residues contribute to control blockage or activation by permeant anions. Finally, R573 mutation abolishes the anomalous mole fraction effect observed in the presence of a permeable anion and it alters the apparent Ca2+-sensitivity of the channel. These findings indicate that residues facing the putative channel pore are responsible both for controlling the ion selectivity and the gating of the channel, providing an initial understanding of molecular mechanism of ion permeation in TMEM16B.
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Affiliation(s)
- Simone Pifferi
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
- * E-mail:
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22
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Contreras-Vite JA, Cruz-Rangel S, De Jesús-Pérez JJ, Figueroa IAA, Rodríguez-Menchaca AA, Pérez-Cornejo P, Hartzell HC, Arreola J. Revealing the activation pathway for TMEM16A chloride channels from macroscopic currents and kinetic models. Pflugers Arch 2016; 468:1241-1257. [PMID: 27138167 DOI: 10.1007/s00424-016-1830-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/19/2016] [Accepted: 04/21/2016] [Indexed: 01/11/2023]
Abstract
TMEM16A (ANO1), the pore-forming subunit of calcium-activated chloride channels, regulates several physiological and pathophysiological processes such as smooth muscle contraction, cardiac and neuronal excitability, salivary secretion, tumour growth and cancer progression. Gating of TMEM16A is complex because it involves the interplay between increases in intracellular calcium concentration ([Ca(2+)]i), membrane depolarization, extracellular Cl(-) or permeant anions and intracellular protons. Our goal here was to understand how these variables regulate TMEM16A gating and to explain four observations. (a) TMEM16A is activated by voltage in the absence of intracellular Ca(2+). (b) The Cl(-) conductance is decreased after reducing extracellular Cl(-) concentration ([Cl(-)]o). (c) ICl is regulated by physiological concentrations of [Cl(-)]o. (d) In cells dialyzed with 0.2 μM [Ca(2+)]i, Cl(-) has a bimodal effect: at [Cl(-)]o <30 mM TMEM16A current activates with a monoexponential time course, but above 30 mM, [Cl(-)]o ICl activation displays fast and slow kinetics. To explain the contribution of Vm, Ca(2+) and Cl(-) to gating, we developed a 12-state Markov chain model. This model explains TMEM16A activation as a sequential, direct, and Vm-dependent binding of two Ca(2+) ions coupled to a Vm-dependent binding of an external Cl(-) ion, with Vm-dependent transitions between states. Our model predicts that extracellular Cl(-) does not alter the apparent Ca(2+) affinity of TMEM16A, which we corroborated experimentally. Rather, extracellular Cl(-) acts by stabilizing the open configuration induced by Ca(2+) and by contributing to the Vm dependence of activation.
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Affiliation(s)
- Juan A Contreras-Vite
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - Silvia Cruz-Rangel
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - Iván A Aréchiga Figueroa
- CONACYT - Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - Aldo A Rodríguez-Menchaca
- Department of Physiology, Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - Patricia Pérez-Cornejo
- Department of Physiology, Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México.
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23
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Reyes JP, Huanosta-Gutiérrez A, López-Rodríguez A, Martínez-Torres A. Study of permeation and blocker binding in TMEM16A calcium-activated chloride channels. Channels (Austin) 2016; 9:88-95. [PMID: 25853341 DOI: 10.1080/19336950.2015.1027849] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
We studied the effects of mutations of positively charged amino acid residues in the pore of X. tropicalis TMEM16A calcium-activated chloride channels: K613E, K628E, K630E; R646E and R761E. The activation and deactivation kinetics were not affected, and only K613E showed a lower current density. K628E and R761E affect anion selectivity without affecting Na(+) permeation, whereas K613E, R646E and the double mutant K613E + R646E affect anion selectivity and permeability to Na(+). Furthermore, altered blockade by the chloride channel blockers anthracene-9-carboxylic acid (A-9-C), 4, 4'-Diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) and T16inh-A01 was observed. These results suggest the existence of 2 binding sites for anions within the pore at electrical distances of 0.3 and 0.5. These sites are also relevant for anion permeation and blockade.
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Affiliation(s)
- J P Reyes
- a Departamento de Neurobiología Celular y Molecular ; Laboratorio de Neurobiología Molecular y Celular ; Instituto de Neurobiología . Campus UNAM Juriquilla; Querétaro, Qro . México
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24
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Whitlock JM, Hartzell HC. A Pore Idea: the ion conduction pathway of TMEM16/ANO proteins is composed partly of lipid. Pflugers Arch 2016; 468:455-73. [PMID: 26739711 PMCID: PMC4751199 DOI: 10.1007/s00424-015-1777-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 12/14/2015] [Accepted: 12/16/2015] [Indexed: 01/04/2023]
Abstract
Since their first descriptions, ion channels have been conceived as proteinaceous conduits that facilitate the passage of ionic cargo between segregated environments. This concept is reinforced by crystallographic structures of cation channels depicting ion conductance pathways completely lined by protein. Although lipids are sometimes present in fenestrations near the pore or may be involved in channel gating, there is little or no evidence that lipids inhabit the ion conduction pathway. Indeed, the presence of lipid acyl chains in the conductance pathway would curse the design of the channel's aqueous pore. Here, we make a speculative proposal that anion channels in the TMEM16/ANO superfamily have ion conductance pathways composed partly of lipids. Our reasoning is based on the idea that TMEM16 ion channels evolved from a kind of lipid transporter that scrambles lipids between leaflets of the membrane bilayer and the modeled structural similarity between TMEM16 lipid scramblases and TMEM16 anion channels. This novel view of the TMEM16 pore offers explanation for the biophysical and pharmacological oddness of TMEM16A. We build upon the recent X-ray structure of nhTMEM16 and develop models of both TMEM16 ion channels and lipid scramblases to bolster our proposal. It is our hope that this model of the TMEM16 pore will foster innovative investigation into TMEM16 function.
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Affiliation(s)
- Jarred M Whitlock
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA.
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25
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De Jesús-Pérez JJ, Castro-Chong A, Shieh RC, Hernández-Carballo CY, De Santiago-Castillo JA, Arreola J. Gating the glutamate gate of CLC-2 chloride channel by pore occupancy. ACTA ACUST UNITED AC 2015; 147:25-37. [PMID: 26666914 PMCID: PMC4692487 DOI: 10.1085/jgp.201511424] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Accepted: 11/17/2015] [Indexed: 11/20/2022]
Abstract
Intracellular permeant anions, and not extracellular protons, are the predominant driver of fast gating in the hyperpolarization-activated CLC-2 chloride channel. CLC-2 channels are dimeric double-barreled chloride channels that open in response to hyperpolarization. Hyperpolarization activates protopore gates that independently regulate the permeability of the pore in each subunit and the common gate that affects the permeability through both pores. CLC-2 channels lack classic transmembrane voltage–sensing domains; instead, their protopore gates (residing within the pore and each formed by the side chain of a glutamate residue) open under repulsion by permeant intracellular anions or protonation by extracellular H+. Here, we show that voltage-dependent gating of CLC-2: (a) is facilitated when permeant anions (Cl−, Br−, SCN−, and I−) are present in the cytosolic side; (b) happens with poorly permeant anions fluoride, glutamate, gluconate, and methanesulfonate present in the cytosolic side; (c) depends on pore occupancy by permeant and poorly permeant anions; (d) is strongly facilitated by multi-ion occupancy; (e) is absent under likely protonation conditions (pHe = 5.5 or 6.5) in cells dialyzed with acetate (an impermeant anion); and (f) was the same at intracellular pH 7.3 and 4.2; and (g) is observed in both whole-cell and inside-out patches exposed to increasing [Cl−]i under unlikely protonation conditions (pHe = 10). Thus, based on our results we propose that hyperpolarization activates CLC-2 mainly by driving intracellular anions into the channel pores, and that protonation by extracellular H+ plays a minor role in dislodging the glutamate gate.
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Affiliation(s)
- José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Alejandra Castro-Chong
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, R.O.C
| | | | | | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
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26
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Cruz-Rangel S, De Jesús-Pérez JJ, Contreras-Vite JA, Pérez-Cornejo P, Hartzell HC, Arreola J. Gating modes of calcium-activated chloride channels TMEM16A and TMEM16B. J Physiol 2015; 593:5283-98. [PMID: 26728431 DOI: 10.1113/jp271256] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 10/12/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Calcium-activated chloride channels TMEM16A and TMEM16B support important physiological processes such as fast block of polyspermy, fluid secretion, control of blood pressure and sensory transduction. Given the physiological importance of TMEM16 channels, it is important to study how incoming stimuli activate these channels. Here we study how channels open and close and how the process of gating is regulated. We show that TMEM16A and TMEM16B display fast and slow gating. These gating modes are regulated by voltage and external chloride. Dual gating explains the complex time course of the anion current. Residues within the first intracellular loop of the channel influence the slow gating mode. Dual gating is an intrinsic property observed in endogenous calcium-activated chloride channels and could be relevant to physiological processes that require sustained chloride ion movement. ABSTRACT TMEM16A and TMEM16B are molecular components of the physiologically relevant calcium-activated chloride channels (CaCCs) present in many tissues. Their gating is dictated by membrane voltage (Vm ), intracellular calcium concentrations ([Ca(2+) ]i ) and external permeant anions. As a consequence, the chloride current (ICl ) kinetics is complex. For example, TMEM16A ICl activates slowly with a non-mono-exponential time course while TMEM16B ICl activates rapidly following a mono-exponential behaviour. To understand the underlying mechanism responsible for the complex activation kinetics, we recorded ICl from HEK-293 cells transiently transfected with either TMEM16A or TMEM16B as well as from mouse parotid acinar cells. Two distinct Vm -dependent gating modes were uncovered: a fast-mode on the millisecond time scale followed by a slow mode on the second time scale. Using long (20 s) depolarizing pulses both gating modes were activated, and a slowly rising ICl was recorded in whole-cell and inside-out patches. The amplitude of ICl at the end of the long pulse nearly doubled and was blocked by 100 μm tannic acid. The slow gating mode was strongly reduced by decreasing the [Cl(-) ]o from 140 to 30 mm and by altering the sequence of the first intracellular loop. Mutating 480 RSQ482 to AVK in the first intracellular loop of TMEM16B nearly abolished slow gating, but, mutating 448 AVK451 to RSQ in TMEM16A has little effect. Deleting 448 EAVK451 residues in TMEM16A reduced slow gating. We conclude that TMEM16 CaCCs have intrinsic Vm - and Cl(-) -sensitive dual gating that elicits complex ICl kinetics.
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Affiliation(s)
- Silvia Cruz-Rangel
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, San Luis Potosí, SLP, 78290, México
| | - José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, San Luis Potosí, SLP, 78290, México
| | - Juan A Contreras-Vite
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, San Luis Potosí, SLP, 78290, México
| | - Patricia Pérez-Cornejo
- Department of Physiology, Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP, 78290, Mexico
| | - H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, San Luis Potosí, SLP, 78290, México
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27
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Napolitano LMR, Bisha I, De March M, Marchesi A, Arcangeletti M, Demitri N, Mazzolini M, Rodriguez A, Magistrato A, Onesti S, Laio A, Torre V. A structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channels. Proc Natl Acad Sci U S A 2015; 112:E3619-28. [PMID: 26100907 PMCID: PMC4500290 DOI: 10.1073/pnas.1503334112] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K(+) channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na(+), Cs(+), and dimethylammonium (DMA(+)), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels.
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Affiliation(s)
| | - Ina Bisha
- International School for Advanced Studies, Trieste 34136, Italy
| | - Matteo De March
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Trieste 34149, Italy
| | - Arin Marchesi
- International School for Advanced Studies, Trieste 34136, Italy
| | | | - Nicola Demitri
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Trieste 34149, Italy
| | | | - Alex Rodriguez
- International School for Advanced Studies, Trieste 34136, Italy
| | - Alessandra Magistrato
- International School for Advanced Studies, Trieste 34136, Italy; National Research Council-Institute of Materials (CNR-IOM)-Democritos National Simulation Center c/o International School for Advanced Studies, Trieste 34136, Italy
| | - Silvia Onesti
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Trieste 34149, Italy;
| | - Alessandro Laio
- International School for Advanced Studies, Trieste 34136, Italy;
| | - Vincent Torre
- International School for Advanced Studies, Trieste 34136, Italy;
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28
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Amjad A, Hernandez-Clavijo A, Pifferi S, Maurya DK, Boccaccio A, Franzot J, Rock J, Menini A. Conditional knockout of TMEM16A/anoctamin1 abolishes the calcium-activated chloride current in mouse vomeronasal sensory neurons. ACTA ACUST UNITED AC 2015; 145:285-301. [PMID: 25779870 PMCID: PMC4380210 DOI: 10.1085/jgp.201411348] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
TMEM16A is an essential component of Ca2+-activated Cl− currents in mouse vomeronasal sensory neurons. Pheromones are substances released from animals that, when detected by the vomeronasal organ of other individuals of the same species, affect their physiology and behavior. Pheromone binding to receptors on microvilli on the dendritic knobs of vomeronasal sensory neurons activates a second messenger cascade to produce an increase in intracellular Ca2+ concentration. Here, we used whole-cell and inside-out patch-clamp analysis to provide a functional characterization of currents activated by Ca2+ in isolated mouse vomeronasal sensory neurons in the absence of intracellular K+. In whole-cell recordings, the average current in 1.5 µM Ca2+ and symmetrical Cl− was −382 pA at −100 mV. Ion substitution experiments and partial blockade by commonly used Cl− channel blockers indicated that Ca2+ activates mainly anionic currents in these neurons. Recordings from inside-out patches from dendritic knobs of mouse vomeronasal sensory neurons confirmed the presence of Ca2+-activated Cl− channels in the knobs and/or microvilli. We compared the electrophysiological properties of the native currents with those mediated by heterologously expressed TMEM16A/anoctamin1 or TMEM16B/anoctamin2 Ca2+-activated Cl− channels, which are coexpressed in microvilli of mouse vomeronasal sensory neurons, and found a closer resemblance to those of TMEM16A. We used the Cre–loxP system to selectively knock out TMEM16A in cells expressing the olfactory marker protein, which is found in mature vomeronasal sensory neurons. Immunohistochemistry confirmed the specific ablation of TMEM16A in vomeronasal neurons. Ca2+-activated currents were abolished in vomeronasal sensory neurons of TMEM16A conditional knockout mice, demonstrating that TMEM16A is an essential component of Ca2+-activated Cl− currents in mouse vomeronasal sensory neurons.
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Affiliation(s)
- Asma Amjad
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
| | - Andres Hernandez-Clavijo
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
| | - Simone Pifferi
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
| | - Devendra Kumar Maurya
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
| | - Anna Boccaccio
- Istituto di Biofisica, National Research Council, 16149 Genova, Italy
| | - Jessica Franzot
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
| | - Jason Rock
- Department of Anatomy, University of California, San Francisco, School of Medicine, San Francisco, CA 94143
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy
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29
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Four basic residues critical for the ion selectivity and pore blocker sensitivity of TMEM16A calcium-activated chloride channels. Proc Natl Acad Sci U S A 2015; 112:3547-52. [PMID: 25733897 DOI: 10.1073/pnas.1502291112] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
TMEM16A (transmembrane protein 16) (Anoctamin-1) forms a calcium-activated chloride channel (CaCC) that regulates a broad array of physiological properties in response to changes in intracellular calcium concentration. Although known to conduct anions according to the Eisenman type I selectivity sequence, the structural determinants of TMEM16A anion selectivity are not well-understood. Reasoning that the positive charges on basic residues are likely contributors to anion selectivity, we performed whole-cell recordings of mutants with alanine substitution for basic residues within the putative pore region and identified four residues on four different putative transmembrane segments that significantly increased the permeability of the larger halides and thiocyanate relative to that of chloride. Because TMEM16A permeation properties are known to shift with changes in intracellular calcium concentration, we further examined the calcium dependence of anion selectivity. We found that WT TMEM16A but not mutants with alanine substitution at those four basic residues exhibited a clear decline in the preference for larger anions as intracellular calcium was increased. Having implicated these residues as contributing to the TMEM16A pore, we scrutinized candidate small molecules from a high-throughput CaCC inhibitor screen to identify two compounds that act as pore blockers. Mutations of those four putative pore-lining basic residues significantly altered the IC50 of these compounds at positive voltages. These findings contribute to our understanding regarding anion permeation of TMEM16A CaCC and provide valuable pharmacological tools to probe the channel pore.
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30
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Cherian OL, Menini A, Boccaccio A. Multiple effects of anthracene-9-carboxylic acid on the TMEM16B/anoctamin2 calcium-activated chloride channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1005-13. [PMID: 25620774 DOI: 10.1016/j.bbamem.2015.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 01/04/2015] [Accepted: 01/13/2015] [Indexed: 10/24/2022]
Abstract
Ca(2+)-activated Cl(-) currents (CaCCs) play important roles in many physiological processes. Recent studies have shown that TMEM16A/anoctamin1 and TMEM16B/anoctamin2 constitute CaCCs in several cell types. Here we have investigated for the first time the extracellular effects of the Cl(-) channel blocker anthracene-9-carboxylic acid (A9C) and of its non-charged analogue anthracene-9-methanol (A9M) on TMEM16B expressed in HEK 293T cells, using the whole-cell patch-clamp technique. A9C caused a voltage-dependent block of outward currents and inhibited a larger fraction of the current as depolarization increased, whereas the non-charged A9M produced a small, not voltage dependent block of outward currents. A similar voltage-dependent block by A9C was measured both when TMEM16B was activated by 1.5 and 13μM Ca(2+). However, in the presence of 1.5μM Ca(2+) (but not in 13μM Ca(2+)), A9C also induced a strong potentiation of tail currents measured at -100mV after depolarizing voltages, as well as a prolongation of the deactivation kinetics. On the contrary, A9M did not produce potentiation of tail currents, showing that the negative charge is required for potentiation. Our results provide the first evidence that A9C has multiple effects on TMEM16B and that the negative charge of A9C is necessary both for voltage-dependent block and for potentiation. Future studies are required to identify the molecular mechanisms underlying these complex effects of A9C on TMEM16B. Understanding these mechanisms will contribute to the elucidation of the structure and functional properties of TMEM16B channels.
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Affiliation(s)
- O Lijo Cherian
- Neurobiology Group, SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, Italy
| | - Anna Menini
- Neurobiology Group, SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, Italy
| | - Anna Boccaccio
- Istituto di Biofisica, CNR, Via De Marini 6, 16149 Genova, Italy.
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31
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Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is unique among ion channels in that after its phosphorylation by protein kinase A (PKA), its ATP-dependent gating violates microscopic reversibility caused by the intimate involvement of ATP hydrolysis in controlling channel closure. Recent studies suggest a gating model featuring an energetic coupling between opening and closing of the gate in CFTR's transmembrane domains and association and dissociation of its two nucleotide-binding domains (NBDs). We found that permeant ions such as nitrate can increase the open probability (Po) of wild-type (WT) CFTR by increasing the opening rate and decreasing the closing rate. Nearly identical effects were seen with a construct in which activity does not require phosphorylation of the regulatory domain, indicating that nitrate primarily affects ATP-dependent gating steps rather than PKA-dependent phosphorylation. Surprisingly, the effects of nitrate on CFTR gating are remarkably similar to those of VX-770 (N-(2,4-Di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide), a potent CFTR potentiator used in clinics. These include effects on single-channel kinetics of WT CFTR, deceleration of the nonhydrolytic closing rate, and potentiation of the Po of the disease-associated mutant G551D. In addition, both VX-770 and nitrate increased the activity of a CFTR construct lacking NBD2 (ΔNBD2), indicating that these gating effects are independent of NBD dimerization. Nonetheless, whereas VX-770 is equally effective when applied from either side of the membrane, nitrate potentiates gating mainly from the cytoplasmic side, implicating a common mechanism for gating modulation mediated through two separate sites of action.
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Affiliation(s)
- Han-I Yeh
- Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
| | - Jiunn-Tyng Yeh
- Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211 Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
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32
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TMEM16 proteins: unknown structure and confusing functions. J Mol Biol 2014; 427:94-105. [PMID: 25451786 DOI: 10.1016/j.jmb.2014.09.028] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 09/24/2014] [Accepted: 09/29/2014] [Indexed: 11/23/2022]
Abstract
The TMEM16 family of membrane proteins, also known as anoctamins, plays key roles in a variety of physiological functions that range from ion transport to phospholipid scrambling and to regulating other ion channels. The first two family members to be functionally characterized, TMEM16A (ANO1) and TMEM16B (ANO2), form Ca(2+)-activated Cl(-) channels and are important for transepithelial ion transport, olfaction, phototransduction, smooth muscle contraction, nociception, cell proliferation and control of neuronal excitability. The roles of other family members, such as TMEM16C (ANO3), TMEM16D (ANO4), TMEM16F (ANO6), TMEM16G (ANO7) and TMEM16J (ANO9), remain poorly understood and controversial. These homologues were reported to be phospholipid scramblases, ion channels, to have both functions or to be regulatory subunits of other channels. Mutations in TMEM16F cause Scott syndrome, a bleeding disorder caused by impaired Ca(2+)-dependent externalization of phosphatidylserine in activated platelets, suggesting that this homologue might be a scramblase. However, overexpression of TMEM16F has also been associated with a remarkable number of different ion channel types, raising the possibility that this protein might be involved in both ion and lipid transports. The recent identification of an ancestral TMEM16 homologue with intrinsic channel and scramblase activities supports this hypothesis. Thus, the TMEM16 family might have diverged in two or three different subclasses, channels, scramblases and dual-function channel/scramblases. The structural bases and functional implication of such a functional diversity within a single protein family remain to be elucidated and the links between TMEM16 functions and human physiology and pathologies need to be investigated.
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33
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Pusch M, Zifarelli G. Thermal sensitivity of CLC and TMEM16 chloride channels and transporters. CURRENT TOPICS IN MEMBRANES 2014; 74:213-31. [PMID: 25366238 DOI: 10.1016/b978-0-12-800181-3.00008-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Cl(-) transport is of fundamental importance in the most diverse physiological contexts and it is mediated by a variety of ion channels and transporters belonging to different protein families. In particular, the recently identified TMEM16 protein family comprises the long sought Ca(2+)-activated Cl(-) channel (CaCC) and the activity of one of its members, TMEM16A, is highly dependent on temperature and is involved in thermal nociception. Among the other protein families mediating Cl(-) transport, CLC proteins are also regulated by temperature although so far the physiological implications of this dependence are unknown.
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