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A large intragenic deletion in the CLCN1 gene causes Hereditary Myotonia in pigs. Sci Rep 2019; 9:15632. [PMID: 31666547 PMCID: PMC6821760 DOI: 10.1038/s41598-019-51286-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 09/11/2019] [Indexed: 12/14/2022] Open
Abstract
Mutations in the CLCN1 gene are the primary cause of non-dystrophic Hereditary Myotonia in several animal species. However, there are no reports of Hereditary Myotonia in pigs to date. Therefore, the objective of the present study was to characterize the clinical and molecular findings of Hereditary Myotonia in an inbred pedigree. The clinical, electromyographic, histopathological, and molecular findings were evaluated. Clinically affected pigs presented non-dystrophic recessive Hereditary Myotonia. Nucleotide sequence analysis of the entire coding region of the CLCN1 gene revealed the absence of the exons 15 and 16 in myotonic animals. Analysis of the genomic region flanking the deletion unveiled a large intragenic deletion of 4,165 nucleotides. Interestingly, non-related, non-myotonic pigs expressed transcriptional levels of an alternate transcript (i.e., X2) that was identical to the deleted X1 transcript of myotonic pigs. All myotonic pigs and their progenitors were homozygous recessive and heterozygous, respectively, for the 4,165-nucleotide deletion. This is the first study reporting Hereditary Myotonia in pigs and characterizing its clinical and molecular findings. Moreover, to the best of our knowledge, Hereditary Myotonia has never been associated with a genomic deletion in the CLCN1 gene in any other species.
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Jentsch TJ, Pusch M. CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease. Physiol Rev 2018; 98:1493-1590. [DOI: 10.1152/physrev.00047.2017] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.
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Affiliation(s)
- Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Michael Pusch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
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3
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Zhang X, Wei Z, He J, Wang C, Zhang Z. Novel mutations of CLCN7 cause autosomal dominant osteopetrosis type II (ADOII) and intermediate autosomal recessive osteopetrosis (ARO) in seven Chinese families. Postgrad Med 2017; 129:934-942. [PMID: 28975865 DOI: 10.1080/00325481.2017.1386529] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Xiaoya Zhang
- Metabolic Bone Disease and Genetic Research Unit, Department of Osteoporosis and Bone Disease, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
| | - Zhanying Wei
- Metabolic Bone Disease and Genetic Research Unit, Department of Osteoporosis and Bone Disease, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
| | - Jinwei He
- Metabolic Bone Disease and Genetic Research Unit, Department of Osteoporosis and Bone Disease, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
| | - Chun Wang
- Metabolic Bone Disease and Genetic Research Unit, Department of Osteoporosis and Bone Disease, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
| | - Zhenlin Zhang
- Metabolic Bone Disease and Genetic Research Unit, Department of Osteoporosis and Bone Disease, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China
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Movement of hClC-1 C-termini during common gating and limits on their cytoplasmic location. Biochem J 2011; 436:415-28. [DOI: 10.1042/bj20102153] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Functionally, the dimeric human skeletal muscle chloride channel hClC-1 is characterized by two distinctive gating processes, fast (protopore) gating and slow (common) gating. Of these, common gating is poorly understood, but extensive conformational rearrangement is suspected. To examine this possibility, we used FRET (fluorescence resonance energy transfer) and assessed the effects of manipulating the common-gating process. Closure of the common gate was accompanied by a separation of the C-termini, whereas, with opening, the C-termini approached each other more closely. These movements were considerably smaller than those seen in ClC-0. To estimate the C-terminus depth within the cytoplasm we constructed a pair of split hClC-1 fragments tagged extracellularly and intracellularly respectively. These not only combined appropriately to rescue channel function, but we detected positive FRET between them. This restricts the C-termini of hClC-1 to a position close to its membrane-resident domain. From mutants in which fast or common gating were affected, FRET revealed a close linkage between the two gating processes with the carboxyl group of Glu232 apparently acting as the final effector for both.
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Feng L, Campbell EB, Hsiung Y, MacKinnon R. Structure of a eukaryotic CLC transporter defines an intermediate state in the transport cycle. Science 2010; 330:635-41. [PMID: 20929736 DOI: 10.1126/science.1195230] [Citation(s) in RCA: 206] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
CLC proteins transport chloride (Cl(-)) ions across cell membranes to control the electrical potential of muscle cells, transfer electrolytes across epithelia, and control the pH and electrolyte composition of intracellular organelles. Some members of this protein family are Cl(-) ion channels, whereas others are secondary active transporters that exchange Cl(-) ions and protons (H(+)) with a 2:1 stoichiometry. We have determined the structure of a eukaryotic CLC transporter at 3.5 angstrom resolution. Cytoplasmic cystathionine beta-synthase (CBS) domains are strategically positioned to regulate the ion-transport pathway, and many disease-causing mutations in human CLCs reside on the CBS-transmembrane interface. Comparison with prokaryotic CLC shows that a gating glutamate residue changes conformation and suggests a basis for 2:1 Cl(-)/H(+) exchange and a simple mechanistic connection between CLC channels and transporters.
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Affiliation(s)
- Liang Feng
- Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA
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Garcia-Olivares J, Alekov A, Boroumand MR, Begemann B, Hidalgo P, Fahlke C. Gating of human ClC-2 chloride channels and regulation by carboxy-terminal domains. J Physiol 2008; 586:5325-36. [PMID: 18801843 DOI: 10.1113/jphysiol.2008.158097] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Eukaryotic ClC channels are dimeric proteins with each subunit forming an individual protopore. Single protopores are gated by a fast gate, whereas the slow gate is assumed to control both protopores through a cooperative movement of the two carboxy-terminal domains. We here study the role of the carboxy-terminal domain in modulating fast and slow gating of human ClC-2 channels, a ubiquitously expressed ClC-type chloride channel involved in transepithelial solute transport and in neuronal chloride homeostasis. Partial truncation of the carboxy-terminus abolishes function of ClC-2 by locking the channel in a closed position. However, unlike other isoforms, its complete removal preserves function of ClC-2. ClC-2 channels without the carboxy-terminus exhibit fast and slow gates that activate and deactivate significantly faster than in WT channels. In contrast to the prevalent view, a single carboxy-terminus suffices for normal slow gating, whereas both domains regulate fast gating of individual protopores. Our findings demonstrate that the carboxy-terminus is not strictly required for slow gating and that the cooperative gating resides in other regions of the channel protein. ClC-2 is expressed in neurons and believed to open at negative potentials and increased internal chloride concentrations after intense synaptic activity. We propose that the function of the ClC-2 carboxy-terminus is to slow down the time course of channel activation in order to stabilize neuronal excitability.
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Affiliation(s)
- Jennie Garcia-Olivares
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
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Abstract
Human ClC-1 (skeletal muscle Cl− channel) has a long cytoplasmic C-tail (carboxyl tail), containing two CBS (cystathionine β-synthase) domains, which is very important for channel function. We have now investigated its significance further, using deletion and alanine-scanning mutagenesis, split channels, GST (glutathione transferase)-pull-down and whole-cell patch-clamping. In tagged split-channel experiments, we have demonstrated strong binding between an N-terminal membrane-resident fragment (terminating mid-C-tail at Ser720 and containing CBS1) and its complement (containing CBS2). This interaction is not affected by deletion of some sequences, suggested previously to be important, particularly in channel gating. Contact between CBS1 and CBS2, however, may make a major contribution to assembly of functional channels from such co-expressed complements, although the possibility that C-tail fragments could, in addition, bind to other parts of the membrane-resident component has not been eliminated. We now show such an interaction between a membrane-resident component terminating at Ser720 (but with CBS1 deleted) and a complete C-tail beginning at Leu598. Channel function is rescued in patch-clamped HEK-293T (human embryonic kidney) cells co-expressing these same fragments. From our own results and those of others, we conclude that the CBS1–CBS2 interaction is not sufficient, in itself, for channel assembly, but rather that this might normally assist in bringing some part of the CBS2/C-tail region into appropriate proximity with the membrane-resident portion of the protein. Previously conflicting and anomalous results can now be explained by an hypothesis that, for split channels to be functional, at least one membrane-resident component must include a plasma membrane trafficking signal between Leu665 and Lys680.
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Jentsch TJ. CLC chloride channels and transporters: from genes to protein structure, pathology and physiology. Crit Rev Biochem Mol Biol 2008; 43:3-36. [PMID: 18307107 DOI: 10.1080/10409230701829110] [Citation(s) in RCA: 277] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
CLC genes are expressed in species from bacteria to human and encode Cl(-)-channels or Cl(-)/H(+)-exchangers. CLC proteins assemble to dimers, with each monomer containing an ion translocation pathway. Some mammalian isoforms need essential beta -subunits (barttin and Ostm1). Crystal structures of bacterial CLC Cl(-)/H(+)-exchangers, combined with transport analysis of mammalian and bacterial CLCs, yielded surprising insights into their structure and function. The large cytosolic carboxy-termini of eukaryotic CLCs contain CBS domains, which may modulate transport activity. Some of these have been crystallized. Mammals express nine CLC isoforms that differ in tissue distribution and subcellular localization. Some of these are plasma membrane Cl(-) channels, which play important roles in transepithelial transport and in dampening muscle excitability. Other CLC proteins localize mainly to the endosomal-lysosomal system where they may facilitate luminal acidification or regulate luminal chloride concentration. All vesicular CLCs may be Cl(-)/H(+)-exchangers, as shown for the endosomal ClC-4 and -5 proteins. Human diseases and knockout mouse models have yielded important insights into their physiology and pathology. Phenotypes and diseases include myotonia, renal salt wasting, kidney stones, deafness, blindness, male infertility, leukodystrophy, osteopetrosis, lysosomal storage disease and defective endocytosis, demonstrating the broad physiological role of CLC-mediated anion transport.
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Affiliation(s)
- Thomas J Jentsch
- Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany.
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Abstract
CLC-0 and cystic fibrosis transmembrane conductance regulator (CFTR) Cl−channels play important roles in Cl−transport across cell membranes. These two proteins belong to, respectively, the CLC and ABC transport protein families whose members encompass both ion channels and transporters. Defective function of members in these two protein families causes various hereditary human diseases. Ion channels and transporters were traditionally viewed as distinct entities in membrane transport physiology, but recent discoveries have blurred the line between these two classes of membrane transport proteins. CLC-0 and CFTR can be considered operationally as ligand-gated channels, though binding of the activating ligands appears to be coupled to an irreversible gating cycle driven by an input of free energy. High-resolution crystallographic structures of bacterial CLC proteins and ABC transporters have led us to a better understanding of the gating properties for CLC and CFTR Cl−channels. Furthermore, the joined force between structural and functional studies of these two protein families has offered a unique opportunity to peek into the evolutionary link between ion channels and transporters. A promising byproduct of this exercise is a deeper mechanistic insight into how different transport proteins work at a fundamental level.
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Macías M, Teijido O, Zifarelli G, Martin P, Ramirez-Espain X, Zorzano A, Palacín M, Pusch M, Estévez R. Myotonia-related mutations in the distal C-terminus of ClC-1 and ClC-0 chloride channels affect the structure of a poly-proline helix. Biochem J 2007; 403:79-87. [PMID: 17107341 PMCID: PMC1828897 DOI: 10.1042/bj20061230] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Myotonia is a state of hyperexcitability of skeletal-muscle fibres. Mutations in the ClC-1 Cl- channel cause recessive and dominant forms of this disease. Mutations have been described throughout the protein-coding region, including three sequence variations (A885P, R894X and P932L) in a distal C-terminal stretch of residues [CTD (C-terminal domain) region] that are not conserved between CLC proteins. We show that surface expression of these mutants is reduced in Xenopus oocytes compared with wild-type ClC-1. Functional, biochemical and NMR spectroscopy studies revealed that the CTD region encompasses a segment conserved in most voltage-dependent CLC channels that folds with a secondary structure containing a short type II poly-proline helix. We found that the myotonia-causing mutation A885P disturbs this structure by extending the poly-proline helix. We hypothesize that this structural modification results in the observed alteration of the common gate that acts on both pores of the channel. We provide the first experimental investigation of structural changes resulting from myotonia-causing mutations.
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Affiliation(s)
- María J. Macías
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
| | - Oscar Teijido
- †Departament de Bioquímica i Biología Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, Barcelona, E-08028, Spain
| | | | - Pau Martin
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
| | - Ximena Ramirez-Espain
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
| | - Antonio Zorzano
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
- †Departament de Bioquímica i Biología Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, Barcelona, E-08028, Spain
| | - Manuel Palacín
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
- †Departament de Bioquímica i Biología Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, Barcelona, E-08028, Spain
| | - Michael Pusch
- ‡Istituto di Biofisica, Via de Marini 6, I-16149 Genova, Italy
| | - Raúl Estévez
- *Institut de Recerca Biomédica, Parc Científic de Barcelona, Josep Samitier 1-5, Barcelona, E-08028, Spain
- †Departament de Bioquímica i Biología Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, Barcelona, E-08028, Spain
- §ZMNH (Zentrum für Molekulare Neurobiologie Hamburg), Hamburg University, Falkenried 94, D-20246 Hamburg, Germany
- To whom correspondence should be addressed (email )
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Li SJ, Kawazaki M, Ogasahara K, Nakagawa A. The Intracellular Region of ClC-3 Chloride Channel Is in a Partially Folded State and a Monomer. ACTA ACUST UNITED AC 2006; 139:813-20. [PMID: 16751588 DOI: 10.1093/jb/mvj099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
In contrast to bacterial ClC chloride channels, all eukaryotic ClC chloride channels have a conserved long intracellular region that makes up of the carboxyl terminus of the protein and is necessary for channel functions as a channel gate. Little is known, however, about the molecular structure of the intracellular region of ClC chloride channels so far. Here, for the first time, we have expressed and purified the intracellular region of the rat ClC-3 chloride channel (C-ClC-3) as a water-soluble protein under physiological conditions, and investigated its structural characteristics and assembly behavior by means of circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC), size exclusion chromatography and analytical ultracentrifugation. The far-UV CD spectra of C-ClC-3 in the native state and in the presence of urea clearly show that the protein has a significantly folded secondary structure consisting of alpha-helices and beta-sheets, while the near-UV CD spectra and DSC experiments indicate the protein is deficient in well-defined tertiary packing. Its Stokes radius is larger than its expected size as a folded globular protein, as determined on size exclusion chromatography. Furthermore, the DisEMBL program, a useful computational tool for the prediction of disordered/unstructured regions within a protein sequence, predicts that the protein is in a partially folded state. Based on these results, we conclude that C-ClC-3 is partially folded. On the other hand, both size exclusion chromatography and sedimentation equilibrium analysis show that C-ClC-3 exists as a monomer in solution, not a dimer like the whole ClC-3 molecule.
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Affiliation(s)
- Shu Jie Li
- Department of Biophysics, College of Physics Science, Nankai University, Tianjin 300071, P. R. China.
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Kuo HC, Hsiao KM, Chang LI, You TH, Yeh TH, Huang CC. Novel mutations at carboxyl terminus of CIC-1 channel in myotonia congenita. Acta Neurol Scand 2006; 113:342-6. [PMID: 16629771 DOI: 10.1111/j.1600-0404.2006.00589.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
OBJECTIVES Myotonia congenita (MC), caused by mutations in the muscle chloride channel (CLCN1) gene, can be inherited dominantly or recessively. The mutations at the carboxyl terminus of the CLCN1 gene have been identified in MC patients, but the functional implication of these mutations is unknown. MATERIAL AND METHODS Direct sequencing of polymerase chain reaction products covering the whole coding region of the CLCN1 gene was performed in a MC family. This study was designed to investigate the clinical manifestations and genetic analysis of the CLCN1 gene. RESULTS We identified two novel mutations, 2330delG and 1892C>T, from a genetic screening of the CLCN1 gene in the MC family. The 2330delG mutant allele producing a fs793X truncated protein was identified in a heterozygous state in all the patients. The 1892C>T nucleotide change induced a missense mutation (T631I) found in several asymptomatic individuals, indicating that it may not be associated with MC. Intriguingly, the 2330delG mutation was also found in an asymptomatic subject who also carried the 1892C>T mutation. CONCLUSION The data indicate that the fs793X mutant protein causes dominantly inherited MC. Because the mutation has been found in a recessive pedigree, the fs793X mutation may have a dual inheritance pattern.
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Affiliation(s)
- H-C Kuo
- Department of Neurology, Chang Gung Memorial Hospital and University, Taipei, Taiwan
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Wu W, Rychkov G, Hughes B, Bretag A. Functional complementation of truncated human skeletal-muscle chloride channel (hClC-1) using carboxyl tail fragments. Biochem J 2006; 395:89-97. [PMID: 16321142 PMCID: PMC1409700 DOI: 10.1042/bj20050966] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Crystal structures of bacterial CLC (voltage-gated chloride channel family) proteins suggest the arrangement of permeation pores and possible gates in the transmembrane region of eukaryotic CLC channels. For the extensive cytoplasmic tails of eukaryotic CLC family members, however, there are no equivalent structural predictions. Truncations of cytoplasmic tails in different places or point mutations result in loss of function or altered gating of several members of the CLC family, suggesting functional importance. In the present study, we show that deletion of the terminal 100 amino acids (N889X) in human ClC-1 (skeletal-muscle chloride channel) has minor consequences, whereas truncation by 110 or more amino acids (from Q879X) destroys channel function. Use of the split channel strategy, co-injecting mRNAs and expressing various complementary constructs in Xenopus oocytes, confirms the importance of the Gln879-Arg888 sequence. A split between the two CBS (cystathionine b-synthase) domains (CBS1 and CBS2) gives normal function (e.g. G721X plus its complement), whereas a partial complementation, eliminating the CBS1 domain, eliminates function. Surprisingly, function is retained even when the region Gly721-Ala862 (between CBS1 and CBS2, and including most of the CBS2 domain) is omitted from the complementation. Furthermore, even shorter peptides from the CBS2-immediate post-CBS2 region are sufficient for functional complementation. We have found that just 26 amino acids from Leu863 to Arg888 are necessary since channel function is restored by co-expressing this peptide with the otherwise inactive truncation, G721X.
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Affiliation(s)
- Weiping Wu
- *Centre for Advanced Biomedical Studies, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia
| | - Grigori Y. Rychkov
- *Centre for Advanced Biomedical Studies, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia
- †School of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA 5005, Australia
| | - Bernard P. Hughes
- *Centre for Advanced Biomedical Studies, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia
| | - Allan H. Bretag
- *Centre for Advanced Biomedical Studies, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia
- To whom correspondence should be addressed (email )
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Hryciw DH, Ekberg J, Ferguson C, Lee A, Wang D, Parton RG, Pollock CA, Yun CC, Poronnik P. Regulation of albumin endocytosis by PSD95/Dlg/ZO-1 (PDZ) scaffolds. Interaction of Na+-H+ exchange regulatory factor-2 with ClC-5. J Biol Chem 2006; 281:16068-77. [PMID: 16601121 DOI: 10.1074/jbc.m512559200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The constitutive reuptake of albumin from the glomerular filtrate by receptor-mediated endocytosis is a key function of the renal proximal tubules. Both the Cl- channel ClC-5 and the Na+-H+ exchanger isoform 3 are critical components of the macromolecular endocytic complex that is required for albumin uptake, and therefore the cell-surface levels of these proteins may limit albumin endocytosis. This study was undertaken to investigate the potential roles of the epithelial PDZ scaffolds, Na+-H+ exchange regulatory factors, NHERF1 and NHERF2, in albumin uptake by opossum kidney (OK) cells. We found that ClC-5 co-immunoprecipitates with NHERF2 but not NHERF1 from OK cell lysate. Experiments using fusion proteins demonstrated that this was a direct interaction between an internal binding site in the C terminus of ClC-5 and the PDZ2 module of NHERF2. In OK cells, NHERF2 is restricted to the intravillar region while NHERF1 is located in the microvilli. Silencing NHERF2 reduced both cell-surface levels of ClC-5 and albumin uptake. Conversely, silencing NHERF1 increased cell-surface levels of ClC-5 and albumin uptake, presumably by increasing the mobility of NHE3 in the membrane and its availability to the albumin uptake complex. Surface biotinylation experiments revealed that both NHERF1 and NHERF2 were associated with the plasma membrane and that NHERF2 was recruited to the membrane in the presence of albumin. The importance of the interaction between NHERF2 and the cytoskeleton was demonstrated by a significant reduction in albumin uptake in cells overexpressing an ezrin binding-deficient mutant of NHERF2. Thus NHERF1 and NHERF2 differentially regulate albumin uptake by mechanisms that ultimately alter the cell-surface levels of ClC-5.
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Affiliation(s)
- Deanne H Hryciw
- School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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Meyer S, Dutzler R. Crystal Structure of the Cytoplasmic Domain of the Chloride Channel ClC-0. Structure 2006; 14:299-307. [PMID: 16472749 DOI: 10.1016/j.str.2005.10.008] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2005] [Revised: 10/26/2005] [Accepted: 10/27/2005] [Indexed: 10/25/2022]
Abstract
Ion channels are frequently organized in a modular fashion and consist of a membrane-embedded pore domain and a soluble regulatory domain. A similar organization is found for the ClC family of Cl- channels and transporters. Here, we describe the crystal structure of the cytoplasmic domain of ClC-0, the voltage-dependent Cl- channel from T. marmorata. The structure contains a folded core of two tightly interacting cystathionine beta-synthetase (CBS) subdomains. The two subdomains are connected by a 96 residue mobile linker that is disordered in the crystals. As revealed by analytical ultracentrifugation, the domains form dimers, thereby most likely extending the 2-fold symmetry of the transmembrane pore. The structure provides insight into the organization of the cytoplasmic domains within the ClC family and establishes a framework for guiding future investigations on regulatory mechanisms.
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Affiliation(s)
- Sebastian Meyer
- Department of Biochemistry, University of Zürich, Winterthurer Strasse 190, CH-8057 Zürich, Switzerland
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Ignoul S, Eggermont J. CBS domains: structure, function, and pathology in human proteins. Am J Physiol Cell Physiol 2005; 289:C1369-78. [PMID: 16275737 DOI: 10.1152/ajpcell.00282.2005] [Citation(s) in RCA: 195] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The cystathionine-β-synthase (CBS) domain is an evolutionarily conserved protein domain that is present in the proteome of archaebacteria, prokaryotes, and eukaryotes. CBS domains usually come in tandem repeats and are found in cytosolic and membrane proteins performing different functions (metabolic enzymes, kinases, and channels). Crystallographic studies of bacterial CBS domains have shown that two CBS domains form an intramolecular dimeric structure (CBS pair). Several human hereditary diseases (homocystinuria, retinitis pigmentosa, hypertrophic cardiomyopathy, myotonia congenital, etc.) can be caused by mutations in CBS domains of, respectively, cystathionine-β-synthase, inosine 5′-monophosphate dehydrogenase, AMP kinase, and chloride channels. Despite their clinical relevance, it remains to be established what the precise function of CBS domains is and how they affect the structural and/or functional properties of an enzyme, kinase, or channel. Depending on the protein in which they occur, CBS domains have been proposed to affect multimerization and sorting of proteins, channel gating, and ligand binding. However, recent experiments revealing that CBS domains can bind adenosine-containing ligands such ATP, AMP, or S-adenosylmethionine have led to the hypothesis that CBS domains function as sensors of intracellular metabolites.
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Affiliation(s)
- Sofie Ignoul
- Laboratory of Physiology, K.U. Leuven, Campus Gasthuisberg O&N, Herestraat 49, B-3000 Leuven, Belgium
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17
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Hebeisen S, Fahlke C. Carboxy-terminal truncations modify the outer pore vestibule of muscle chloride channels. Biophys J 2005; 89:1710-20. [PMID: 15980168 PMCID: PMC1366675 DOI: 10.1529/biophysj.104.056093] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mammalian ClC-type chloride channels have large cytoplasmic carboxy-terminal domains whose function is still insufficiently understood. We investigated the role of the distal part of the carboxy-terminus of the muscle isoform ClC-1 by constructing and functionally evaluating two truncation mutants, R894X and K875X. Truncated channels exhibit normal unitary conductances and anion selectivities but altered apparent anion binding affinities in the open and in the closed state. Since voltage-dependent gating is strictly coupled to ion permeation in ClC-1 channels, the changed pore properties result in different fast and slow gating. Full length and truncated channels also differed in methanethiosulphonate (MTS) modification rate constants of an engineered cysteine at position 231 near the selectivity filter. Our data demonstrate that the carboxy-terminus of ClC channels modifies the conformation of the outer pore vestibule.
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Abstract
The CLC family comprises a group of integral membrane proteins whose major action is to translocate chloride (Cl-) ions across the cell membranes. Recently, the structures of CLC orthologues from two bacterial species, Salmonella typhimurium and Escherichia coli, were solved, providing the first framework for understanding the operating mechanisms of these molecules. However, most of the previous mechanistic understanding of CLC channels came from electrophysiological studies of a branch of the channel family, the muscle-type CLC channels in vertebrate species. These vertebrate CLC channels were predicted to contain two identical but independent pores, and this hypothesis was confirmed by the solved bacterial CLC structures. The opening and closing of the vertebrate CLC channels are also known to couple to the permeant ions via their binding sites in the ion-permeation pathway. The bacterial CLC structures can probably serve as a structural model to explain the gating-permeation coupling mechanism. However, the CLC-ec1 protein in E. coli was most recently shown to be a Cl- -H+ antiporter, but not an ion channel. The molecular basis to explain the difference between vertebrate and bacterial CLCs, especially the distinction between an ion channel and a transporter, remains a challenge in the structure/function studies for the CLC family.
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Affiliation(s)
- Tsung-Yu Chen
- Center for Neuroscience and Department of Neurology, University of California, Davis, California 95616, USA.
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Chen L, Schaerer M, Lu ZH, Lang D, Joncourt F, Weis J, Fritschi J, Kappeler L, Gallati S, Sigel E, Burgunder JM. Exon 17 skipping in CLCN1 leads to recessive myotonia congenita. Muscle Nerve 2004; 29:670-6. [PMID: 15116370 DOI: 10.1002/mus.20005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Mutations in CLCN1, the gene encoding the ClC-1 chloride channel in skeletal muscle, lead to myotonia congenita. The effects on the intramembranous channel forming domains have been investigated more than that at the intracellular C-terminus. We have performed a mutation screen involving the whole CLCN1 gene of patients with myotonia congenita by polymerase chain reaction (PCR), single-strand conformation polymorphism studies, and sequencing. Two unrelated patients harbored the same homozygous G-to-T mutation on the donor splice site of intron 17. This led to the skipping of exon 17, as evidenced by the reverse transcriptase PCR. When the exon 17-deleted CLCN1 was expressed in Xenopus oocytes, no chloride current was measurable. This function could be restored by coexpression with the wild-type channel. Our data suggest an important role of this C-terminal region and that exon 17 skipping resulting from a homozygous point mutation in CLCN1 can lead to recessive myotonia congenita.
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Affiliation(s)
- Lie Chen
- Departments of Neurology and Clinical Research, Laboratory of Neuromorphology, University of Berne, Berne, Switzerland
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20
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Hebeisen S, Biela A, Giese B, Müller-Newen G, Hidalgo P, Fahlke C. The Role of the Carboxyl Terminus in ClC Chloride Channel Function. J Biol Chem 2004; 279:13140-7. [PMID: 14718533 DOI: 10.1074/jbc.m312649200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human muscle chloride channel ClC-1 has a 398-amino acid carboxyl-terminal domain that resides in the cytoplasm and contains two CBS (cystathionine-beta-synthase) domains. To examine the role of this region, we studied various carboxyl-terminal truncations by heterologous expression in mammalian cells, whole-cell patch clamp recording, and confocal imaging. Channel constructs lacking parts of the distal CBS domain, CBS2, did not produce functional channels, whereas deletion of CBS1 was tolerated. ClC channels are dimeric proteins with two ion conduction pathways (protopores). In heterodimeric channels consisting of one wild type subunit and one subunit in which the carboxyl terminus was completely deleted, only the wild type protopore was functional, indicating that the carboxyl terminus supports the function of the protopore. All carboxyl-terminal-truncated mutant channels fused to yellow fluorescent protein were translated and the majority inserted into the plasma membrane as revealed by confocal microscopy. Fusion proteins of cyan fluorescent protein linked to various fragments of the carboxyl terminus formed soluble proteins that could be redistributed to the surface membrane through binding to certain truncated channel subunits. Stable binding only occurs between carboxyl-terminal fragments of a single subunit, not between carboxyl termini of different subunits and not between carboxyl-terminal and transmembrane domains. However, an interaction with transmembrane domains can modify the binding properties of particular carboxyl-terminal proteins. Our results demonstrate that the carboxyl terminus of ClC-1 is not necessary for intracellular trafficking but is critical for channel function. Carboxyl termini fold independently and modify individual protopores of the double-barreled channel.
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Affiliation(s)
- Simon Hebeisen
- Institutes of Physiology, Rheinisch-Westfälische Technische Hochschule Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany
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Estévez R, Pusch M, Ferrer-Costa C, Orozco M, Jentsch TJ. Functional and structural conservation of CBS domains from CLC chloride channels. J Physiol 2004; 557:363-78. [PMID: 14724190 PMCID: PMC1665104 DOI: 10.1113/jphysiol.2003.058453] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
All eukaryotic CLC Cl(-) channel subunits possess a long cytoplasmic carboxy-terminus that contains two so-called CBS (cystathionine beta-synthase) domains. These domains are found in various unrelated proteins from all phylae. The crystal structure of the CBS domains of inosine monophosphate dehydrogenase (IMPDH) is known, but it is not known whether this structure is conserved in CLC channels. Working primarily with ClC-1, we used deletion scanning mutagenesis, coimmunoprecipitation and electrophysiology to demonstrate that its CBS domains interact. The replacement of CBS domains of ClC-1 with the corresponding CBS domains from other CLC channels and even human IMPDH yielded functional channels, indicating a high degree of structural conservation. Based on a homology model of the pair of CBS domains of CLC channels, we identified some residues that, when mutated, affected the common gate which acts on both pores of the dimeric channel. Thus, we propose that the structure of CBS domains from CLC channels is highly conserved and that they play a functional role in the common gate.
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Affiliation(s)
- Raúl Estévez
- Zentrum für Molekulare Neurobiologie Hamburg (ZMNH), Hamburg University, Falkenried 94, D-20246 Hamburg, Germany
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22
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Mo L, Xiong W, Qian T, Sun H, Wills NK. Coexpression of complementary fragments of ClC-5 and restoration of chloride channel function in a Dent's disease mutation. Am J Physiol Cell Physiol 2004; 286:C79-89. [PMID: 13679301 DOI: 10.1152/ajpcell.00009.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human hereditary disorder Dent's disease is linked to loss-of-function mutations of the chloride channel ClC-5. Many of these mutations involve insertion of premature stop codons, resulting in truncation of the protein. We determined whether the functional activity of ClC-5 could be restored by coexpression of the truncated protein (containing the NH2-terminal region) with its complementary “missing” COOH-terminal region. Split channel constructs for ClC-5, consisting of complementary N and C protein regions, were created at an arbitrary site in the COOH-terminal region (V655) and at four Dent's disease mutation sites (R347, Y617, R648, and R704). Coexpression of complementary fragments for the split channel at V655 produced currents with anion and pH sensitivity similar to those of wild-type ClC-5. Channel activity was similarly restored when complementary split channel constructs made for Dent's mutation R648 were coexpressed, but no ClC-5 currents were found when split channels for mutations R347, Y617, or R704 were coexpressed. Immunoblot and immunofluorescence studies of COS-7 cells revealed that N or C protein fragments could be transiently expressed and detected in the plasma membrane, even in split channels that failed to show functional activity. The results suggest that ClC-5 channel activity can be restored for specific Dent's mutations by expression of the missing portion of the ClC-5 molecule.
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Affiliation(s)
- L Mo
- Departments of Physiology & Biophysics, University of Texas Medical Branch, Galveston, TX 77555-0641, USA
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Carr G, Simmons N, Sayer J. A role for CBS domain 2 in trafficking of chloride channel CLC-5. Biochem Biophys Res Commun 2003; 310:600-5. [PMID: 14521953 DOI: 10.1016/j.bbrc.2003.09.057] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
CLC-5 is a member of the CLC family of voltage-gated chloride channels. Mutations disrupting CLC-5 lead to Dent's disease, an X-linked renal tubular disorder, characterised by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis, and renal stones. Sequence analysis of CLC-5 reveals a 746 amino acid protein with an intracellular amino-terminus, transmembrane spanning domains, and two CBS domains within its intracellular carboxy-terminus. CBS domains have been implicated in intracellular targetting and trafficking as well as protein-protein interactions. We investigate subcellular localisation of three naturally occurring CLC-5 mutants which all lead to a truncated protein, disrupting the second CBS domain. These mutants are unable to traffic normally to acidic endosomes but are retained in perinuclear compartments, colocalising with the Golgi complex. This is the first identification of the cellular pathogenesis of CBS domain mutations of CLC-5.
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Affiliation(s)
- Georgina Carr
- School of Cell and Molecular Biosciences, University of Newcastle, Framlington Place, Newcastle Upon Tyne NE2 4HH, UK
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24
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Abstract
CLC chloride channels form a large gene family that is found in bacteria, archae and eukaryotes. Previous mutagenesis studies on CLC chloride channels, combined with electrophysiology, strongly supported the theory that these channels form a homodimeric structure with one pore per subunit (a'double-barrelled' channel), and also provided clues about gating and permeation. Recently, the crystal structures of two bacterial CLC proteins have been obtained by X-ray diffraction analysis. They confirm the double-barrelled architecture, and reveal a surprisingly complex and unprecedented channel structure. At its binding site in the pore, chloride interacts with the ends of four helices that come from both sides of the membrane. A glutamate residue that protrudes into the pore is proposed to participate in gating. The structure confirms several previous conclusions from mutagenesis studies and provides an excellent framework for their interpretation.
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Affiliation(s)
- Raúl Estévez
- Zentrum für Molekulare Neurobiologie, Universität Hamburg, Falkenried 94, Germany
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Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 2002; 82:503-68. [PMID: 11917096 DOI: 10.1152/physrev.00029.2001] [Citation(s) in RCA: 925] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.
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Affiliation(s)
- Thomas J Jentsch
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Hamburg, Germany.
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26
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Waldegger S, Jentsch TJ. From tonus to tonicity: physiology of CLC chloride channels. J Am Soc Nephrol 2000; 11:1331-1339. [PMID: 10864591 DOI: 10.1681/asn.v1171331] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Chloride channels are involved in a multitude of physiologic processes ranging from basal cellular functions such as cell volume regulation and acidification of intracellular vesicles to more specialized mechanisms such as vectorial transepithelial transport and regulation of cellular excitability. This plethora of functions is accomplished by numerous functionally highly diverse chloride channels that are only partially identified at the molecular level. The CLC family of chloride channels comprises at present nine members in mammals that differ with respect to biophysical properties, cellular compartmentalization, and tissue distribution. Their common structural features include a predicted topology model with 10 to 12 transmembrane regions together with two C-terminal CBS domains. Loss of function mutations affecting three different members of the CLC channel family lead to three human inherited diseases : myotonia congenita, Dent's disease, and Bartter's syndrome. These diseases, together with the diabetes insipidus symptoms of a knockout mouse model, emphasize the physiologic relevance of this ion channel family.
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Affiliation(s)
| | - Thomas J Jentsch
- Center for Molecular Neurobiology (ZMNH), University of Hamburg, Germany
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27
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Abstract
The field of molecular physiology of ClC chloride channels has witnessed a tremendous surge in knowledge over the past few years; however, fundamental issues such as the stoichiometry of ClC channels and the identification of pore-lining sequences have only recently begun to be addressed. New studies have also provided important insights into the role of ClC channels in cell volume regulation and their function in intracellular organelles.
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Affiliation(s)
- M A Valverde
- Department de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, C/Dr. Aiguader 80, 08003, Barcelona, Spain.
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28
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Schwappach B, Stobrawa S, Hechenberger M, Steinmeyer K, Jentsch TJ. Golgi localization and functionally important domains in the NH2 and COOH terminus of the yeast CLC putative chloride channel Gef1p. J Biol Chem 1998; 273:15110-8. [PMID: 9614122 DOI: 10.1074/jbc.273.24.15110] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GEF1 encodes the single CLC putative chloride channel in yeast. Its disruption leads to a defect in iron metabolism (Greene, J. R., Brown, N. H., DiDomenico, B. J., Kaplan, J., and Eide, D. (1993) Mol. Gen. Genet. 241, 542-553). Since disruption of GEF2, a subunit of the vacuolar H+-ATPase, leads to a similar phenotype, it was previously suggested that the chloride conductance provided by Gef1p is necessary for vacuolar acidification. We now show that gef1 cells indeed grow less well at less acidic pH. However, no defect in vacuolar acidification is apparent from quinacrine staining, and Gef1p co-localizes with Mnt1p in the medial Golgi. Thus, Gef1p may be important in determining Golgi pH. Systematic alanine scanning of the amino and the carboxyl terminus revealed several regions essential for Gef1p localization and function. One sequence (FVTID) in the amino terminus conforms to a class of sorting signals containing aromatic amino acids. This was further supported by point mutations. Alanine scanning of the carboxyl terminus identified a stretch of roughly 25 amino acids which coincides with the second CBS domain, a conserved protein motif recently identified. Mutations in the first CBS domain also destroyed proper function and localization. The second CBS domain can be transplanted to the amino terminus without loss of function, but could not be replaced by the corresponding domain of the homologous mammalian channel ClC-2.
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Affiliation(s)
- B Schwappach
- Zentrum für Molekulare Neurobiologie Hamburg (ZMNH), Hamburg University, Martinistrasse 52, D-20246 Hamburg, Germany
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