1
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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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2
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Moran O, Tammaro P. Identification of determinants of lipid and ion transport in TMEM16/anoctamin proteins through a Bayesian statistical analysis. Biophys Chem 2024; 308:107194. [PMID: 38401241 DOI: 10.1016/j.bpc.2024.107194] [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: 12/16/2023] [Revised: 01/17/2024] [Accepted: 01/28/2024] [Indexed: 02/26/2024]
Abstract
The TMEM16/Anoctamin protein family (TMEM16x) is composed of members with different functions; some members form Ca2+-activated chloride channels, while others are lipid scramblases or combine the two functions. TMEM16x proteins are typically activated in response to agonist-induced rises of intracellular Ca2+; thus, they couple Ca2+-signalling with cell electrical activity or plasmalemmal lipid homeostasis. The structural domains underlying these functions are not fully defined. We used a Naïve Bayes classifier to gain insights into these domains. The method enabled identification of regions involved in either ion or lipid transport, and suggested domains for possible pharmacological exploitation. The method allowed the prediction of the transport property of any given TMEM16x. We envisage this strategy could be exploited to illuminate the structure-function relationship of any protein family composed of members playing different molecular roles.
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Affiliation(s)
- Oscar Moran
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), Via De Marini 6, 16149 Genova, Italy
| | - Paolo Tammaro
- Department Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
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3
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Zhang Y, Wu K, Li Y, Wu S, Warshel A, Bai C. Predicting Mutational Effects on Ca 2+-Activated Chloride Conduction of TMEM16A Based on a Simulation Study. J Am Chem Soc 2024; 146:4665-4679. [PMID: 38319142 DOI: 10.1021/jacs.3c11940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
The dysfunction and defects of ion channels are associated with many human diseases, especially for loss-of-function mutations in ion channels such as cystic fibrosis transmembrane conductance regulator mutations in cystic fibrosis. Understanding ion channels is of great current importance for both medical and fundamental purposes. Such an understanding should include the ability to predict mutational effects and describe functional and mechanistic effects. In this work, we introduce an approach to predict mutational effects based on kinetic information (including reaction barriers and transition state locations) obtained by studying the working mechanism of target proteins. Specifically, we take the Ca2+-activated chloride channel TMEM16A as an example and utilize the computational biology model to predict the mutational effects of key residues. Encouragingly, we verified our predictions through electrophysiological experiments, demonstrating a 94% prediction accuracy regarding mutational directions. The mutational strength assessed by Pearson's correlation coefficient is -0.80 between our calculations and the experimental results. These findings suggest that the proposed methodology is reliable and can provide valuable guidance for revealing functional mechanisms and identifying key residues of the TMEM16A channel. The proposed approach can be extended to a broad scope of biophysical systems.
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Affiliation(s)
- Yue Zhang
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
| | - Kang Wu
- South China Hospital, Health Science Center, Shenzhen University, Shenzhen 518116, China
| | - Yuqing Li
- South China Hospital, Health Science Center, Shenzhen University, Shenzhen 518116, China
| | - Song Wu
- South China Hospital, Health Science Center, Shenzhen University, Shenzhen 518116, China
| | - Arieh Warshel
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062, United States
| | - Chen Bai
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China
- Chenzhu Biotechnology Co., Ltd., Hangzhou 310005, China
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4
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Lowry AJ, Liang P, Wan YCS, Pei ZM, Yang H, Zhang Y. TMEM16 and TMEM63/OSCA proteins share a conserved potential to permeate ions and phospholipids. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.04.578431. [PMID: 38370744 PMCID: PMC10871192 DOI: 10.1101/2024.02.04.578431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
The calcium-activated TMEM16 proteins and the mechanosensitive/osmolarity-activated OSCA/TMEM63 proteins belong to the Transmembrane Channel/Scramblase (TCS) superfamily. Within the superfamily, OSCA/TMEM63 proteins, as well as TMEM16A and TMEM16B, likely function solely as ion channels. However, the remaining TMEM16 members, including TMEM16F, maintain an additional function as scramblases, rapidly exchanging phospholipids between leaflets of the membrane. Although recent studies have advanced our understanding of TCS structure-function relationships, the molecular determinants of TCS ion and lipid permeation remain unclear. Here we show that single lysine mutations in transmembrane helix (TM) 4 allow non-scrambling TCS members to permeate phospholipids. This study highlights the key role of TM 4 in controlling TCS ion and lipid permeation and offers novel insights into the evolution of the TCS superfamily, suggesting that, like TMEM16s, the OSCA/TMEM63 family maintains a conserved potential to permeate ions and phospholipids.
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Affiliation(s)
- Augustus J Lowry
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Pengfei Liang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Y C Serena Wan
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Zhen-Ming Pei
- Department of Biology, Duke University, Durham, NC 27710, USA
| | - Huanghe Yang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
- Department of Neurobiology, Duke University School of Medicine, Durham, NC 27710, USA
| | - Yang Zhang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
- Current address: Shenzhen Bay Laboratory, Guangdong 518106, China
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5
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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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6
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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: 0] [Impact Index Per Article: 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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7
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Lam AKM, Dutzler R. Mechanistic basis of ligand efficacy in the calcium-activated chloride channel TMEM16A. EMBO J 2023; 42:e115030. [PMID: 37984335 PMCID: PMC10711664 DOI: 10.15252/embj.2023115030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 10/27/2023] [Accepted: 11/02/2023] [Indexed: 11/22/2023] Open
Abstract
Agonist binding in ligand-gated ion channels is coupled to structural rearrangements around the binding site, followed by the opening of the channel pore. In this process, agonist efficacy describes the equilibrium between open and closed conformations in a fully ligand-bound state. Calcium-activated chloride channels in the TMEM16 family are important sensors of intracellular calcium signals and are targets for pharmacological modulators, yet a mechanistic understanding of agonist efficacy has remained elusive. Using a combination of cryo-electron microscopy, electrophysiology, and autocorrelation analysis, we now show that agonist efficacy in the ligand-gated channel TMEM16A is dictated by the conformation of the pore-lining helix α6 around the Ca2+ -binding site. The closure of the binding site, which involves the formation of a π-helix below a hinge region in α6, appears to be coupled to the opening of the inner pore gate, thereby governing the channel's open probability and conductance. Our results provide a mechanism for agonist binding and efficacy and a structural basis for the design of potentiators and partial agonists in the TMEM16 family.
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Affiliation(s)
- Andy KM Lam
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Raimund Dutzler
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
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Elverson K, Freeman S, Manson F, Warwicker J. Computational Investigation of Mechanisms for pH Modulation of Human Chloride Channels. Molecules 2023; 28:5753. [PMID: 37570721 PMCID: PMC10420675 DOI: 10.3390/molecules28155753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 07/25/2023] [Accepted: 07/26/2023] [Indexed: 08/13/2023] Open
Abstract
Many transmembrane proteins are modulated by intracellular or extracellular pH. Investigation of pH dependence generally proceeds by mutagenesis of a wide set of amino acids, guided by properties such as amino-acid conservation and structure. Prediction of pKas can streamline this process, allowing rapid and effective identification of amino acids of interest with respect to pH dependence. Commencing with the calcium-activated chloride channel bestrophin 1, the carboxylate ligand structure around calcium sites relaxes in the absence of calcium, consistent with a measured lack of pH dependence. By contrast, less relaxation in the absence of calcium in TMEM16A, and maintenance of elevated carboxylate sidechain pKas, is suggested to give rise to pH-dependent chloride channel activity. This hypothesis, modulation of calcium/proton coupling and pH-dependent activity through the extent of structural relaxation, is shown to apply to the well-characterised cytosolic proteins calmodulin (pH-independent) and calbindin D9k (pH-dependent). Further application of destabilised, ionisable charge sites, or electrostatic frustration, is made to other human chloride channels (that are not calcium-activated), ClC-2, GABAA, and GlyR. Experimentally determined sites of pH modulation are readily identified. Structure-based tools for pKa prediction are freely available, allowing users to focus on mutagenesis studies, construct hypothetical proton pathways, and derive hypotheses such as the model for control of pH-dependent calcium activation through structural flexibility. Predicting altered pH dependence for mutations in ion channel disorders can support experimentation and, ultimately, clinical intervention.
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Affiliation(s)
- Kathleen Elverson
- Division of Evolution, Infection and Genomics, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Sally Freeman
- Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Forbes Manson
- Division of Evolution, Infection and Genomics, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Jim Warwicker
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, Manchester Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, UK
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9
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Ma T, Wang L, Chai A, Liu C, Cui W, Yuan S, Wing Ngor Au S, Sun L, Zhang X, Zhang Z, Lu J, Gao Y, Wang P, Li Z, Liang Y, Vogel H, Wang YT, Wang D, Yan K, Zhang H. Cryo-EM structures of ClC-2 chloride channel reveal the blocking mechanism of its specific inhibitor AK-42. Nat Commun 2023; 14:3424. [PMID: 37296152 PMCID: PMC10256776 DOI: 10.1038/s41467-023-39218-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 06/02/2023] [Indexed: 06/12/2023] Open
Abstract
ClC-2 transports chloride ions across plasma membranes and plays critical roles in cellular homeostasis. Its dysfunction is involved in diseases including leukodystrophy and primary aldosteronism. AK-42 was recently reported as a specific inhibitor of ClC-2. However, experimental structures are still missing to decipher its inhibition mechanism. Here, we present cryo-EM structures of apo ClC-2 and its complex with AK-42, both at 3.5 Å resolution. Residues S162, E205 and Y553 are involved in chloride binding and contribute to the ion selectivity. The side-chain of the gating glutamate E205 occupies the putative central chloride-binding site, indicating that our structure represents a closed state. Structural analysis, molecular dynamics and electrophysiological recordings identify key residues to interact with AK-42. Several AK-42 interacting residues are present in ClC-2 but not in other ClCs, providing a possible explanation for AK-42 specificity. Taken together, our results experimentally reveal the potential inhibition mechanism of ClC-2 inhibitor AK-42.
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Grants
- National Natural Science Foundation of China (National Science Foundation of China)
- National Science and Technology Innovation 2030 Major Program (No. 2022ZD0211900)
- the Science and Technology Innovation Committee of Shenzhen(No. JCYJ20200109150700942), the Key-Area Research and Development Program of Guangdong Province (2019B030335001), the Shenzhen Fund for Guangdong Provincial High Level Clinical Key Specialties (No. SZGSP013), and the Shenzhen Key Medical Discipline Construction Fund (No. SZXK042)
- The Shenzhen Key Laboratory of Computer Aided Drug Discovery, Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, 518055, China, Funding number: ZDSYS20201230165400001. The Chinese Academy of Science President’s International Fellowship Initiative (PIFI) (No. 2020FSB0003), Guangdong Retired Expert (granted by Guangdong Province), National Overseas High Level Talent Introduction Plan-Foreign Expert from Organization Department of the CPC Central Committee (1000 talent project), Shenzhen Pengcheng Scientist, NSFC-SNSF Funding (No. 32161133022), AlphaMol & SIAT Joint Laboratory, Shenzhen Government Top-talent Working Funding and Guangdong Province Academician Work Funding.
- NSFC-Guangdong Joint Fund-U20A6005, Shenzhen Key Laboratory of Translational Research for Brain Diseases (ZDSYS20200828154800001)
- Shenzhen Science and Technology Program (No. JCYJ20220530115214033 and No. KQTD20210811090115021)
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Affiliation(s)
- Tao Ma
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Lei Wang
- School of Life Sciences, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Anping Chai
- Shenzhen Key Laboratory of Translational Research for Brain Diseases, The Brain Cognition and Brain Disease Institute, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
- Shenzhen-Hong Kong Institute of Brain Science-Shenzhen Fundamental Research Institutions, 518055, Shenzhen, Guangdong, China
| | - Chao Liu
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Wenqiang Cui
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Shuguang Yuan
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China
| | - Shannon Wing Ngor Au
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China
| | - Liang Sun
- Shenzhen Shuli Tech Co., Ltd, 518126, Shenzhen, Guangdong, China
| | - Xiaokang Zhang
- Shenzhen-Hong Kong Institute of Brain Science-Shenzhen Fundamental Research Institutions, 518055, Shenzhen, Guangdong, China
- Interdisciplinary Center for Brain Information, The Brain Cognition and Brain Disease Institute, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, Guangdong, China
- Faculty of Life and Health Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, Guangdong, China
| | - Zhenzhen Zhang
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Jianping Lu
- Department of Child and Adolescent Psychiatry, Shenzhen Kangning Hospital, Shenzhen Mental Health Center, Shenzhen, 518020, China
| | - Yuanzhu Gao
- Cryo-EM Facility Center, Southern University of Science and Technology, 518055, Shenzhen, Guangdong, China
| | - Peiyi Wang
- Cryo-EM Facility Center, Southern University of Science and Technology, 518055, Shenzhen, Guangdong, China
| | - Zhifang Li
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Yujie Liang
- Department of Child and Adolescent Psychiatry, Shenzhen Kangning Hospital, Shenzhen Mental Health Center, Shenzhen, 518020, China
| | - Horst Vogel
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China.
- Institut des Sciences et Ingénierie Chimiques (ISIC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
| | - Yu Tian Wang
- Shenzhen Key Laboratory of Translational Research for Brain Diseases, The Brain Cognition and Brain Disease Institute, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.
- Faculty of Life and Health Sciences, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, Guangdong, China.
| | - Daping Wang
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China.
- Department of Orthopedics, Shenzhen Intelligent Orthopaedics and Biomedical Innovation Platform, Guangdong Provincial Research Center for Artificial Intelligence and Digital Orthopedic Technology, Shenzhen Second People's Hospital, The First Affiliated Hospital of Shenzhen University, 518000, Shenzhen, China.
| | - Kaige Yan
- School of Life Sciences, Southern University of Science and Technology, 518055, Shenzhen, China.
| | - Huawei Zhang
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, 518055, Shenzhen, China.
- Department of Biomedical Engineering, Southern University of Science and Technology, 518055, Shenzhen, China.
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10
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Shi S, Ma B, Ji Q, Guo S, An H, Ye S. Identification of a druggable pocket of the calcium-activated chloride channel TMEM16A in its open state. J Biol Chem 2023:104780. [PMID: 37142220 DOI: 10.1016/j.jbc.2023.104780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 04/25/2023] [Accepted: 04/27/2023] [Indexed: 05/06/2023] Open
Abstract
The calcium-activated chloride channel TMEM16A is a potential drug target to treat hypertension, secretory diarrhea, and several cancers. However, all reported TMEM16A structures are either closed or desensitized, and direct inhibition of the open state by drug molecules lacks a reliable structural basis. Therefore, revealing the druggable pocket of TMEM16A exposed in the open state is important for understanding protein-ligand interactions and facilitating rational drug design. Here, we reconstructed the calcium-activated open conformation of TMEM16A using an enhanced sampling algorithm and segmental modeling. Furthermore, we identified an open state druggable pocket and screened a potent TMEM16A inhibitor, etoposide, which is a derivative of a traditional herbal monomer. Molecular simulations and site-directed mutagenesis showed that etoposide binds to the open state of TMEM16A, thereby blocking the ion conductance pore of the channel. Finally, we demonstrated that etoposide can target TMEM16A to inhibit the proliferation of prostate cancer PC-3 cells. Together, these findings provide a deep understanding of the TMEM16A open state at an atomic level and identify pockets for the design of novel inhibitors with broad applications in chloride channel biology, biophysics, and medicinal chemistry.
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Affiliation(s)
- Sai Shi
- Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, Tianjin, 300072, China
| | - Biao Ma
- State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China
| | - Qiushuang Ji
- School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, 300072, China
| | - Shuai Guo
- School of Life Sciences, Hebei University, Baoding 071002, Hebei, China.
| | - Hailong An
- State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China.
| | - Sheng Ye
- Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, Tianjin, 300072, China.
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11
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Arreola J, López-Romero AE, Pérez-Cornejo P, Rodríguez-Menchaca AA. Phosphatidylinositol 4,5-Bisphosphate and Cholesterol Regulators of the Calcium-Activated Chloride Channels TMEM16A and TMEM16B. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1422:279-304. [PMID: 36988885 DOI: 10.1007/978-3-031-21547-6_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Chloride fluxes through homo-dimeric calcium-activated channels TMEM16A and TMEM16B are critical to blood pressure, gastrointestinal motility, hormone, fluid and electrolyte secretion, pain sensation, sensory transduction, and neuronal and muscle excitability. Their gating depends on the voltage-dependent binding of two intracellular calcium ions to a high-affinity site formed by acidic residues from α-helices 6-8 in each monomer. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), a low-abundant lipid of the inner leaflet, supports TMEM16A function; it allows TMEM16A to evade the down-regulation induced by calcium, poly-L-lysine, or PI(4,5)P2 5-phosphatase. In stark contrast, adding or removing PI(4,5)P2 diminishes or increases TMEM16B function, respectively. PI(4,5)P2-binding sites on TMEM16A, and presumably on TMEM16B, are on the cytosolic side of α-helices 3-5, opposite the calcium-binding sites. This modular structure suggested that PI(4,5)P2 and calcium cooperate to maintain the conductive state in TMEM16A. Cholesterol, the second-largest constituent of the plasma membrane, also regulates TMEM16A though the mechanism, functional outcomes, binding site(s), and effects on TMEM16A and TMEM16B remain unknown.
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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, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
| | - Aldo A Rodríguez-Menchaca
- Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
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12
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Thangaratnarajah C, Rheinberger J, Paulino C. Cryo-EM studies of membrane proteins at 200 keV. Curr Opin Struct Biol 2022; 76:102440. [PMID: 36029606 DOI: 10.1016/j.sbi.2022.102440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Revised: 07/01/2022] [Accepted: 07/06/2022] [Indexed: 11/03/2022]
Abstract
Single-particle cryogenic electron-microscopy (cryo-EM) has emerged as a powerful technique for the structural characterisation of membrane proteins, especially for targets previously thought to be intractable. Taking advantage of the latest hard- and software developments, high-resolution three-dimensional (3D) reconstructions of membrane proteins by cryo-EM has become routine, with 300-kV transmission electron microscopes (TEMs) being the current standard. The use of 200-kV cryo-TEMs is gaining increasingly prominence, showing the capabilities of reaching better than 2 Å resolution for soluble proteins and better than 3 Å resolution for membrane proteins. Here, we highlight the challenges working with membrane proteins and the impact of cryo-EM, and review the technical and practical benefits, achievements and limitations of imaging at lower electron acceleration voltages.
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Affiliation(s)
- Chancievan Thangaratnarajah
- University of Groningen, Faculty of Science and Engineering, Groningen Biomolecular Sciences and Biotechnology, Electron Microscopy and Membrane Enzymology Group, Nijenborgh 4, 9747 AG, Groningen, Netherlands.
| | - Jan Rheinberger
- University of Groningen, Faculty of Science and Engineering, Groningen Biomolecular Sciences and Biotechnology, Electron Microscopy and Membrane Enzymology Group, Nijenborgh 4, 9747 AG, Groningen, Netherlands. https://twitter.com/rheinbergerj
| | - Cristina Paulino
- University of Groningen, Faculty of Science and Engineering, Groningen Biomolecular Sciences and Biotechnology, Electron Microscopy and Membrane Enzymology Group, Nijenborgh 4, 9747 AG, Groningen, Netherlands.
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13
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Tembo M, Bainbridge RE, Lara-Santos C, Komondor KM, Daskivich GJ, Durrant JD, Rosenbaum JC, Carlson AE. Phosphate position is key in mediating transmembrane ion channel TMEM16A-phosphatidylinositol 4,5-bisphosphate interaction. J Biol Chem 2022; 298:102264. [PMID: 35843309 PMCID: PMC9396059 DOI: 10.1016/j.jbc.2022.102264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 07/10/2022] [Accepted: 07/11/2022] [Indexed: 02/07/2023] Open
Abstract
TransMEMbrane 16A (TMEM16A) is a Ca2+-activated Cl- channel that plays critical roles in regulating diverse physiologic processes, including vascular tone, sensory signal transduction, and mucosal secretion. In addition to Ca2+, TMEM16A activation requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). However, the structural determinants mediating this interaction are not clear. Here, we interrogated the parts of the PI(4,5)P2 head group that mediate its interaction with TMEM16A by using patch- and two-electrode voltage-clamp recordings on oocytes from the African clawed frog Xenopus laevis, which endogenously express TMEM16A channels. During continuous application of Ca2+ to excised inside-out patches, we found that TMEM16A-conducted currents decayed shortly after patch excision. Following this rundown, we show that the application of a synthetic PI(4,5)P2 analog produced current recovery. Furthermore, inducible dephosphorylation of PI(4,5)P2 reduces TMEM16A-conducted currents. Application of PIP2 analogs with different phosphate orientations yielded distinct amounts of current recovery, and only lipids that include a phosphate at the 4' position effectively recovered TMEM16A currents. Taken together, these findings improve our understanding of how PI(4,5)P2 binds to and potentiates TMEM16A channels.
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Affiliation(s)
- Maiwase Tembo
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Rachel E Bainbridge
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Crystal Lara-Santos
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Kayla M Komondor
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Grant J Daskivich
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Jacob D Durrant
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Joel C Rosenbaum
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Anne E Carlson
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
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14
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Evolutionary history of metazoan TMEM16 family. Mol Phylogenet Evol 2022; 177:107595. [PMID: 35914647 DOI: 10.1016/j.ympev.2022.107595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Revised: 07/16/2022] [Accepted: 07/26/2022] [Indexed: 11/22/2022]
Abstract
Most of Transmembrane protein 16 (TMEM16) proteins function as either a Ca2+-activated Cl- channel (CaCC) or phospholipid scramblase (CaPLSase) and play diverse physiological roles. It is well conserved in eukaryotes; however, the origin and evolution of different subfamilies in Metazoa are not yet understood. To uncover the evolutionary history of the TMEM16 family, we analyzed 398 proteins from 74 invertebrate species using evolutionary genomics. We found that the TMEM16C-F and J subfamilies are vertebrate-specific, but the TMEM16A/B, G, H, and K subfamilies are ancient and present in many, but not all metazoan species. The most ancient subfamilies in Metazoa, TMEM16L and M, are only maintained in limited species. TMEM16N and O are Cnidaria- and Ecdysozoa-specific subfamilies, respectively, and Ctenophora, Xenacoelomorpha, and Rotifera contain species-specific proteins. We also identified TMEM16 genes that are closely linked together in the genome, suggesting that they have been generated via recent gene duplication. The anoctamin domain structures of invertebrate-specific TMEM16 proteins predicted by AlphaFold2 contain conserved Ca2+-binding motifs and permeation pathways with either narrow or wide inner gates. The inner gate distance of TMEM16 protein may have frequently switched during metazoan evolution, and thus determined the function of the protein as either CaCC or CaPLSase. These results demonstrate that TMEM16 family has evolved by gene gain and loss in metazoans, and the genes have been generally under purifying selection to maintain protein structures and physiological functions.
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15
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Zhang Y, Zhu X, Zhang H, Yan J, Xu P, Wu P, Wu S, Bai C. Mechanism Study of Proteins under Membrane Environment. MEMBRANES 2022; 12:membranes12070694. [PMID: 35877897 PMCID: PMC9322369 DOI: 10.3390/membranes12070694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Revised: 07/01/2022] [Accepted: 07/05/2022] [Indexed: 11/24/2022]
Abstract
Membrane proteins play crucial roles in various physiological processes, including molecule transport across membranes, cell communication, and signal transduction. Approximately 60% of known drug targets are membrane proteins. There is a significant need to deeply understand the working mechanism of membrane proteins in detail, which is a challenging work due to the lack of available membrane structures and their large spatial scale. Membrane proteins carry out vital physiological functions through conformational changes. In the current study, we utilized a coarse-grained (CG) model to investigate three representative membrane protein systems: the TMEM16A channel, the family C GPCRs mGlu2 receptor, and the P4-ATPase phospholipid transporter. We constructed the reaction pathway of conformational changes between the two-end structures. Energy profiles and energy barriers were calculated. These data could provide reasonable explanations for TMEM16A activation, the mGlu2 receptor activation process, and P4-ATPase phospholipid transport. Although they all belong to the members of membrane proteins, they behave differently in terms of energy. Our work investigated the working mechanism of membrane proteins and could give novel insights into other membrane protein systems of interest.
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Affiliation(s)
- Yue Zhang
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
- Warshel Institute for Computational Biology, Shenzhen 518172, China
| | - Xiaohong Zhu
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
- Warshel Institute for Computational Biology, Shenzhen 518172, China
| | - Honghui Zhang
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- Warshel Institute for Computational Biology, Shenzhen 518172, China
| | - Junfang Yan
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- Warshel Institute for Computational Biology, Shenzhen 518172, China
| | - Peiyi Xu
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- Warshel Institute for Computational Biology, Shenzhen 518172, China
| | - Peng Wu
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen 518055, China;
| | - Song Wu
- South China Hospital, Health Science Center, Shenzhen University, Shenzhen 518116, China
- Correspondence: (S.W.); (C.B.)
| | - Chen Bai
- School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China; (Y.Z.); (X.Z.); (H.Z.); (J.Y.); (P.X.)
- Warshel Institute for Computational Biology, Shenzhen 518172, China
- Chenzhu Biotechnology Co., Ltd., Hangzhou 310005, China
- Correspondence: (S.W.); (C.B.)
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16
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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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17
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Lam AKM, Rutz S, Dutzler R. Inhibition mechanism of the chloride channel TMEM16A by the pore blocker 1PBC. Nat Commun 2022; 13:2798. [PMID: 35589730 PMCID: PMC9120017 DOI: 10.1038/s41467-022-30479-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/29/2022] [Indexed: 11/09/2022] Open
Abstract
TMEM16A, a calcium-activated chloride channel involved in multiple cellular processes, is a proposed target for diseases such as hypertension, asthma, and cystic fibrosis. Despite these therapeutic promises, its pharmacology remains poorly understood. Here, we present a cryo-EM structure of TMEM16A in complex with the channel blocker 1PBC and a detailed functional analysis of its inhibition mechanism. A pocket located external to the neck region of the hourglass-shaped pore is responsible for open-channel block by 1PBC and presumably also by its structural analogs. The binding of the blocker stabilizes an open-like conformation of the channel that involves a rearrangement of several pore helices. The expansion of the outer pore enhances blocker sensitivity and enables 1PBC to bind at a site within the transmembrane electric field. Our results define the mechanism of inhibition and gating and will facilitate the design of new, potent TMEM16A modulators.
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Affiliation(s)
- Andy K M Lam
- Department of Biochemistry, University of Zurich, Winterthurer Str. 190, CH-8057, Zurich, Switzerland.
| | - Sonja Rutz
- Department of Biochemistry, University of Zurich, Winterthurer Str. 190, CH-8057, Zurich, Switzerland
| | - Raimund Dutzler
- Department of Biochemistry, University of Zurich, Winterthurer Str. 190, CH-8057, Zurich, Switzerland.
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18
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Beverley KM, Shahi PK, Kabra M, Zhao Q, Heyrman J, Steffen J, Pattnaik BR. Kir7.1 disease mutant T153I within the inner pore affects K+ conduction. Am J Physiol Cell Physiol 2022; 323:C56-C68. [PMID: 35584325 DOI: 10.1152/ajpcell.00093.2022] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Inward-rectifier potassium channel 7.1 (Kir7.1) is present in polarized epithelium, including the RPE. A single amino acid change at position 153 in the KCNJ13 gene, a substitution of threonine to isoleucine in Kir7.1 protein, causes blindness. We hypothesized that the disease caused by this single amino acid substitution within the transmembrane protein domain could alter the translation, localization, or ion transport properties. We assessed the effects of amino acid side-chain length, arrangement, and polarity on channel structure and function. We showed that the T153I mutation yielded a full-length protein localized to the cell membrane. Whole-cell patch-clamp recordings and chord conductance analyses revealed that the T153I mutant channel had negligible K+ conductance and failed to hyperpolarize the membrane potential. However, the mutant channel exhibited enhanced inward current when Rb+ was used as a charge carrier, suggesting that an inner pore had formed, and the channel was dysfunctional. Substituting with a polar, non-polar, or short side-chain amino acid did not affect the localization of the protein. Still, it had an altered channel function due to differences in pore radius. Polar side chains (cysteine and serine) with inner pore radii comparable to wildtype exhibited normal inward K+ conductance. Short side-chains (glycine and alanine) produced a channel with wider than expected inner pore size and lacked the biophysical characteristics of the wildtype channel. Leucine substitution produced results similar to the T153I mutant channel. This study provides direct electrophysiological evidence for the structure and function of the Kir7.1 channel's narrow inner pore in regulating conductance.
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Affiliation(s)
- Katie M Beverley
- Endocrinology and Reproductive Physiology Graduate Program, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,McPherson Eye Research Institute, University of Wisconsin, Madison, WI, United States
| | - Pawan K Shahi
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,McPherson Eye Research Institute, University of Wisconsin, Madison, WI, United States
| | - Meha Kabra
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,McPherson Eye Research Institute, University of Wisconsin, Madison, WI, United States
| | - Qianqian Zhao
- Department of Biostatistics and Medical Informatics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Joseph Heyrman
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Jack Steffen
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Bikash R Pattnaik
- Endocrinology and Reproductive Physiology Graduate Program, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States.,McPherson Eye Research Institute, University of Wisconsin, Madison, WI, United States.,Department of Ophthalmology and Visual Sciences, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
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19
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Wang G, Nauseef WM. Neutrophil dysfunction in the pathogenesis of cystic fibrosis. Blood 2022; 139:2622-2631. [PMID: 35213685 PMCID: PMC9053701 DOI: 10.1182/blood.2021014699] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 01/31/2022] [Indexed: 11/20/2022] Open
Abstract
Polymorphonuclear neutrophils (PMNs) figure prominently in host defense against infection and in noninfectious inflammation. Mobilized early in an inflammatory response, PMNs mediate immediate cellular defense against microbes and orchestrate events that culminate in cessation of inflammation and restoration of homeostasis. Failure to terminate the inflammatory response and its causes can fuel exuberant inflammation characteristic of many human diseases, including cystic fibrosis (CF), an autosomal recessive genetic disease caused by mutations in the CF transmembrane conductance regulator. CF affects multiple end organs, with persistent bacterial infection and chronic neutrophilic inflammation in airways predominating the clinical picture. To match the diverse microbial challenges that they may encounter, PMNs possess a variety of antimicrobial systems to slow or kill invading microorganisms confined in their phagosomes. Prominent among PMN defense systems is their ability to generate hypochlorous acid, a potent microbicide, by reacting oxidants generated by the NADPH oxidase with myeloperoxidase (MPO) released from azurophilic granules in the presence of chloride (Cl-). Products of the MPO-H2O2-Cl system oxidize susceptible biomolecules and support robust antimicrobial action against many, but not all, potential human pathogens. Underscoring that the MPO-H2O2-Cl system is integral to optimal host defense and proper regulation of inflammation, individuals with defects in any component of this system, as seen in chronic granulomatous disease or MPO deficiency, incur increased rates or severity of infection and signs of dysregulated inflammatory responses. We focus attention in this review on the molecular basis for and the clinical consequences of defects in the MPO-H2O2-Cl system because of the compromised Cl transport seen in CF. We will discuss first how the MPO-H2O2-Cl system in healthy PMNs participates in host defense and resolution of inflammation and then review how a defective MPO-H2O2-Cl system contributes to the increased susceptibility to infection and dysregulated inflammation associated with the clinical manifestations of CF.
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Affiliation(s)
- Guoshun Wang
- Department of Microbiology, Immunology, and Parasitology, and
- Department of Genetics, Louisiana State University Health Sciences Center, New Orleans, LA
| | - William M Nauseef
- Inflammation Program, Department of Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA; and
- Veterans Administration Medical Center, Iowa City, IA
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20
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Shi S, Pang C, Ren S, Sun F, Ma B, Guo S, Li J, Chen Y, An H. Molecular dynamics simulation of TMEM16A channel: Linking structure with gating. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183777. [PMID: 34537214 DOI: 10.1016/j.bbamem.2021.183777] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Revised: 08/23/2021] [Accepted: 09/12/2021] [Indexed: 10/20/2022]
Abstract
TMEM16A, the calcium-activated chloride channel, is broadly expressed and plays pivotal roles in diverse physiological processes. To understand the structural and functional relationships of TMEM16A, it is necessary to fully clarify the structural basis of the gating of the TMEM16A channel. Herein, we performed the protein electrostatic analysis and molecular dynamics simulation on the TMEM16A in the presence and absence of Ca2+. Data showed that the separation of TM4 and TM6 causes pore expansion, and Q646 may be a key residue for the formation of π-helix in the middle segment of TM6. Moreover, E705 was found to form a group of H-bond interactions with D554/K588/K645 below the hydrophobic gate to stabilize the closed conformation of the pore in the Ca2+-free state. Interestingly, in the Ca2+ bound state, the E705 side chain swings 100o to serve as Ca2+-binding coordination and released K645. K645 is closer to the hydrophobic gate in the calcium-bound state, which facilitates the provision of electrostatic forces for chloride ions as the ions pass through the hydrophobic gate. Our findings provide the structural-based insights to understanding the mechanisms of gating of TMEM16A.
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Affiliation(s)
- Sai Shi
- State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Chunli Pang
- Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Shuxi Ren
- Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Fude Sun
- Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Biao Ma
- State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Shuai Guo
- College of Life Science, Hebei University, Baoding 071002, Hebei, China
| | - Junwei Li
- Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Yafei Chen
- Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China
| | - Hailong An
- State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province, Hebei University of Technology, Tianjin 300401, China; Key Laboratory of Molecular Biophysics of Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401, China.
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21
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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: 5] [Impact Index Per Article: 2.5] [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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22
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Jeong H, Clark S, Goehring A, Dehghani-Ghahnaviyeh S, Rasouli A, Tajkhorshid E, Gouaux E. Structures of the TMC-1 complex illuminate mechanosensory transduction. Nature 2022; 610:796-803. [PMID: 36224384 PMCID: PMC9605866 DOI: 10.1038/s41586-022-05314-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 08/02/2022] [Indexed: 02/05/2023]
Abstract
The initial step in the sensory transduction pathway underpinning hearing and balance in mammals involves the conversion of force into the gating of a mechanosensory transduction channel1. Despite the profound socioeconomic impacts of hearing disorders and the fundamental biological significance of understanding mechanosensory transduction, the composition, structure and mechanism of the mechanosensory transduction complex have remained poorly characterized. Here we report the single-particle cryo-electron microscopy structure of the native transmembrane channel-like protein 1 (TMC-1) mechanosensory transduction complex isolated from Caenorhabditis elegans. The two-fold symmetric complex is composed of two copies each of the pore-forming TMC-1 subunit, the calcium-binding protein CALM-1 and the transmembrane inner ear protein TMIE. CALM-1 makes extensive contacts with the cytoplasmic face of the TMC-1 subunits, whereas the single-pass TMIE subunits reside on the periphery of the complex, poised like the handles of an accordion. A subset of complexes additionally includes a single arrestin-like protein, arrestin domain protein (ARRD-6), bound to a CALM-1 subunit. Single-particle reconstructions and molecular dynamics simulations show how the mechanosensory transduction complex deforms the membrane bilayer and suggest crucial roles for lipid-protein interactions in the mechanism by which mechanical force is transduced to ion channel gating.
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Affiliation(s)
- Hanbin Jeong
- grid.433851.80000 0004 0608 3919Vollum Institute, Oregon Health and Science University, Portland, OR USA
| | - Sarah Clark
- grid.433851.80000 0004 0608 3919Vollum Institute, Oregon Health and Science University, Portland, OR USA
| | - April Goehring
- grid.433851.80000 0004 0608 3919Vollum Institute, Oregon Health and Science University, Portland, OR USA ,grid.5288.70000 0000 9758 5690Howard Hughes Medical Institute, Oregon Health and Science University, Portland, OR USA
| | - Sepehr Dehghani-Ghahnaviyeh
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
| | - Ali Rasouli
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
| | - Emad Tajkhorshid
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL USA ,grid.35403.310000 0004 1936 9991Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
| | - Eric Gouaux
- grid.433851.80000 0004 0608 3919Vollum Institute, Oregon Health and Science University, Portland, OR USA ,grid.5288.70000 0000 9758 5690Howard Hughes Medical Institute, Oregon Health and Science University, Portland, OR USA
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23
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Hawn MB, Akin E, Hartzell H, Greenwood IA, Leblanc N. Molecular mechanisms of activation and regulation of ANO1-Encoded Ca 2+-Activated Cl - channels. Channels (Austin) 2021; 15:569-603. [PMID: 34488544 PMCID: PMC8480199 DOI: 10.1080/19336950.2021.1975411] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 08/29/2021] [Indexed: 01/13/2023] Open
Abstract
Ca2+-activated Cl- channels (CaCCs) perform a multitude of functions including the control of cell excitability, regulation of cell volume and ionic homeostasis, exocrine and endocrine secretion, fertilization, amplification of olfactory sensory function, and control of smooth muscle cell contractility. CaCCs are the translated products of two members (ANO1 and ANO2, also known as TMEM16A and TMEM16B) of the Anoctamin family of genes comprising ten paralogs. This review focuses on recent progress in understanding the molecular mechanisms involved in the regulation of ANO1 by cytoplasmic Ca2+, post-translational modifications, and how the channel protein interacts with membrane lipids and protein partners. After first reviewing the basic properties of native CaCCs, we then present a brief historical perspective highlighting controversies about their molecular identity in native cells. This is followed by a summary of the fundamental biophysical and structural properties of ANO1. We specifically address whether the channel is directly activated by internal Ca2+ or indirectly through the intervention of the Ca2+-binding protein Calmodulin (CaM), and the structural domains responsible for Ca2+- and voltage-dependent gating. We then review the regulation of ANO1 by internal ATP, Calmodulin-dependent protein kinase II-(CaMKII)-mediated phosphorylation and phosphatase activity, membrane lipids such as the phospholipid phosphatidyl-(4,5)-bisphosphate (PIP2), free fatty acids and cholesterol, and the cytoskeleton. The article ends with a survey of physical and functional interactions of ANO1 with other membrane proteins such as CLCA1/2, inositol trisphosphate and ryanodine receptors in the endoplasmic reticulum, several members of the TRP channel family, and the ancillary Κ+ channel β subunits KCNE1/5.
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Affiliation(s)
- M. B. Hawn
- Department of Pharmacology and Center of Biomedical Research Excellence for Molecular and Cellular Signal Transduction in the Cardiovascular System, University of Nevada, Reno School of Medicine, Reno, United States
| | - E. Akin
- Department of Pharmacology and Center of Biomedical Research Excellence for Molecular and Cellular Signal Transduction in the Cardiovascular System, University of Nevada, Reno School of Medicine, Reno, United States
| | - H.C. Hartzell
- Department of Cell Biology, Emory University School of Medicine, USA
| | - I. A. Greenwood
- Department of Vascular Pharmacology, St. George’s University of London, UK
| | - N. Leblanc
- Department of Pharmacology and Center of Biomedical Research Excellence for Molecular and Cellular Signal Transduction in the Cardiovascular System, University of Nevada, Reno School of Medicine, Reno, United States
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24
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Le SC, Liang P, Lowry AJ, Yang H. Gating and Regulatory Mechanisms of TMEM16 Ion Channels and Scramblases. Front Physiol 2021; 12:787773. [PMID: 34867487 PMCID: PMC8640346 DOI: 10.3389/fphys.2021.787773] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 10/29/2021] [Indexed: 12/30/2022] Open
Abstract
The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated ion channels and Ca2+-activated phospholipid scramblases (CaPLSases) that passively flip-flop phospholipids between the two leaflets of the membrane bilayer. Owing to their diverse functions, TMEM16 proteins have been implicated in various human diseases, including asthma, cancer, bleeding disorders, muscular dystrophy, arthritis, epilepsy, dystonia, ataxia, and viral infection. To understand TMEM16 proteins in health and disease, it is critical to decipher their molecular mechanisms of activation gating and regulation. Structural, biophysical, and computational characterizations over the past decade have greatly advanced the molecular understanding of TMEM16 proteins. In this review, we summarize major structural features of the TMEM16 proteins with a focus on regulatory mechanisms and gating.
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Affiliation(s)
- Son C. Le
- Department of Biochemistry, Duke University Medical Center, Durham, NC, United States
| | - Pengfei Liang
- Department of Biochemistry, Duke University Medical Center, Durham, NC, United States
| | - Augustus J. Lowry
- Department of Biochemistry, Duke University Medical Center, Durham, NC, United States
| | - Huanghe Yang
- Department of Biochemistry, Duke University Medical Center, Durham, NC, United States
- Department of Neurobiology, Duke University Medical Center, Durham, NC, United States
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25
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Abstract
TMEM16A Ca2+-activated chloride channels are involved in multiple cellular functions and are proposed targets for diseases such as hypertension, stroke, and cystic fibrosis. This therapeutic endeavor, however, suffers from paucity of selective and potent modulators. Here, exploiting a synthetic small molecule with a biphasic effect on the TMEM16A channel, anthracene-9-carboxylic acid (A9C), we shed light on sites of the channel amenable for pharmacological intervention. Mutant channels with the intracellular gate constitutively open were generated. These channels were entirely insensitive to extracellular A9C when intracellular Ca2+ was omitted. However, when physiological Ca2+ levels were reestablished, the mutants regained sensitivity to A9C. Thus, intracellular Ca2+ is mandatory for the channel response to an extracellular modulator. The underlying mechanism is a conformational change in the outer pore that enables A9C to enter the pore to reach its binding site. The explanation of this structural rearrangement highlights a critical site for pharmacological intervention and reveals an aspect of Ca2+ gating in the TMEM16A channel.
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26
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Rheinberger J, Oostergetel G, Resch GP, Paulino C. Optimized cryo-EM data-acquisition workflow by sample-thickness determination. Acta Crystallogr D Struct Biol 2021; 77:565-571. [PMID: 33950013 PMCID: PMC8098475 DOI: 10.1107/s205979832100334x] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Accepted: 03/29/2021] [Indexed: 12/19/2022] Open
Abstract
Sample thickness is a known key parameter in cryo-electron microscopy (cryo-EM) and can affect the amount of high-resolution information retained in the image. Yet, common data-acquisition approaches in single-particle cryo-EM do not take it into account. Here, it is demonstrated how the sample thickness can be determined before data acquisition, allowing the identification of optimal regions and the restriction of automated data collection to images with preserved high-resolution details. This quality-over-quantity approach almost entirely eliminates the time- and storage-consuming collection of suboptimal images, which are discarded after a recorded session or during early image processing due to a lack of high-resolution information. It maximizes the data-collection efficiency and lowers the electron-microscopy time required per data set. This strategy is especially useful if the speed of data collection is restricted by the microscope hardware and software, or if microscope access time, data transfer, data storage and computational power are a bottleneck.
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Affiliation(s)
- Jan Rheinberger
- Department of Structural Biology and Membrane Enzymology at the Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Gert Oostergetel
- Department of Structural Biology and Membrane Enzymology at the Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Guenter P. Resch
- Nexperion e.U. – Solutions for Electron Microscopy, Vienna, Austria
| | - Cristina Paulino
- Department of Structural Biology and Membrane Enzymology at the Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
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27
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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: 50] [Impact Index Per Article: 16.7] [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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28
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Lam AKM, Dutzler R. Mechanism of pore opening in the calcium-activated chloride channel TMEM16A. Nat Commun 2021; 12:786. [PMID: 33542228 PMCID: PMC7862263 DOI: 10.1038/s41467-020-20788-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 12/16/2020] [Indexed: 01/14/2023] Open
Abstract
The anion channel TMEM16A is activated by intracellular Ca2+ in a highly cooperative process. By combining electrophysiology and autocorrelation analysis, we investigated the mechanism of channel activation and the concurrent rearrangement of the gate in the narrow part of the pore. Features in the fluctuation characteristics of steady-state current indicate the sampling of intermediate conformations that are successively occupied during gating. The initial step is related to conformational changes induced by Ca2+ binding, which is ensued by rearrangements that open the pore. Mutations in the gate shift the equilibrium of transitions in a manner consistent with a progressive destabilization of this region during pore opening. We come up with a mechanism of channel activation where the binding of Ca2+ induces conformational changes in the protein that, in a sequential manner, propagate from the binding site and couple to the gate in the narrow pore to allow ion permeation.
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Affiliation(s)
- Andy K M Lam
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
| | - Raimund Dutzler
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
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