51
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Conformational changes required for H(+)/Cl(-) exchange mediated by a CLC transporter. Nat Struct Mol Biol 2014; 21:456-63. [PMID: 24747941 PMCID: PMC4040230 DOI: 10.1038/nsmb.2814] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Accepted: 03/26/2014] [Indexed: 11/08/2022]
Abstract
CLC-type exchangers mediate transmembrane Cl(-) transport. Mutations altering their gating properties cause numerous genetic disorders. However, their transport mechanism remains poorly understood. In conventional models, two gates alternatively expose substrates to the intra- or extracellular solutions. A glutamate was identified as the only gate in the CLCs, suggesting that CLCs function by a nonconventional mechanism. Here we show that transport in CLC-ec1, a prokaryotic homolog, is inhibited by cross-links constraining movement of helix O far from the transport pathway. Cross-linked CLC-ec1 adopts a wild-type-like structure, indicating stabilization of a native conformation. Movements of helix O are transduced to the ion pathway via a direct contact between its C terminus and a tyrosine that is a constitutive element of the second gate of CLC transporters. Therefore, the CLC exchangers have two gates that are coupled through conformational rearrangements outside the ion pathway.
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52
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Ulzi G, Sansone VA, Magri F, Corti S, Bresolin N, Comi GP, Lucchiari S. In vitro analysis of splice site mutations in the CLCN1 gene using the minigene assay. Mol Biol Rep 2014; 41:2865-74. [PMID: 24452722 DOI: 10.1007/s11033-014-3142-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 01/11/2014] [Indexed: 12/21/2022]
Abstract
Mutations in the chloride channel gene CLCN1 cause the allelic disorders Thomsen (dominant) and Becker (recessive) myotonia congenita (MC). The encoded protein, ClC-1, is the primary channel that mediates chloride (Cl-) conductance in skeletal muscle. Mutations in CLCN1 lower the channel's threshold voltage, leading to spontaneous action potentials that are not coupled to neuromuscular transmission and resulting in myotonia. Over 120 mutations in CLCN1 have been described, 10% of which are splicing defects. Biological specimens suitable for RNA extraction are not always available, but obtaining genomic DNA for analysis is easy and non-invasive. This is the first study to evaluate the pathogenic potential of novel splicing mutations using the minigene approach, which is based on genomic DNA analysis. Splicing mutations accounted for 23% of all pathogenic variants in our cohort of MC patients. Four were heterozygous mutations in four unrelated individuals, belonging to this cohort: c.563G>T in exon 5; c.1169-5T>G in intron 10; c.1251+1G>A in intron 11, and c.1931-2A>G in intron 16. These variants were expressed in HEK 293 cells, and aberrant splicing was verified by in vitro transcription and sequencing of the cDNA. Our findings confirm the need to further investigate the nature of rearrangements associated with this class of mutations and their effects on mature transcripts. In particular, splicing mutations predicted to generate in-frame transcripts may generate out-of-frame mRNA transcripts that do not produce functional ClC-1. Clinically, incomplete molecular evaluation could lead to delayed or faulty diagnosis.
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Affiliation(s)
- Gianna Ulzi
- Neurology Unit, Neuroscience Section, Department of Pathophysiology and Transplantation (DEPT), Dino Ferrari Centre, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, University of Milan, Via Sforza 35, 20122, Milan, Italy
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53
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Pusch M, Zifarelli G. Thermal sensitivity of CLC and TMEM16 chloride channels and transporters. CURRENT TOPICS IN MEMBRANES 2014; 74:213-31. [PMID: 25366238 DOI: 10.1016/b978-0-12-800181-3.00008-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Cl(-) transport is of fundamental importance in the most diverse physiological contexts and it is mediated by a variety of ion channels and transporters belonging to different protein families. In particular, the recently identified TMEM16 protein family comprises the long sought Ca(2+)-activated Cl(-) channel (CaCC) and the activity of one of its members, TMEM16A, is highly dependent on temperature and is involved in thermal nociception. Among the other protein families mediating Cl(-) transport, CLC proteins are also regulated by temperature although so far the physiological implications of this dependence are unknown.
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54
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Stauber T, Weinert S, Jentsch TJ. Cell biology and physiology of CLC chloride channels and transporters. Compr Physiol 2013; 2:1701-44. [PMID: 23723021 DOI: 10.1002/cphy.c110038] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Proteins of the CLC gene family assemble to homo- or sometimes heterodimers and either function as Cl(-) channels or as Cl(-)/H(+)-exchangers. CLC proteins are present in all phyla. Detailed structural information is available from crystal structures of bacterial and algal CLCs. Mammals express nine CLC genes, four of which encode Cl(-) channels and five 2Cl(-)/H(+)-exchangers. Two accessory β-subunits are known: (1) barttin and (2) Ostm1. ClC-Ka and ClC-Kb Cl(-) channels need barttin, whereas Ostm1 is required for the function of the lysosomal ClC-7 2Cl(-)/H(+)-exchanger. ClC-1, -2, -Ka and -Kb Cl(-) channels reside in the plasma membrane and function in the control of electrical excitability of muscles or neurons, in extra- and intracellular ion homeostasis, and in transepithelial transport. The mainly endosomal/lysosomal Cl(-)/H(+)-exchangers ClC-3 to ClC-7 may facilitate vesicular acidification by shunting currents of proton pumps and increase vesicular Cl(-) concentration. ClC-3 is also present on synaptic vesicles, whereas ClC-4 and -5 can reach the plasma membrane to some extent. ClC-7/Ostm1 is coinserted with the vesicular H(+)-ATPase into the acid-secreting ruffled border membrane of osteoclasts. Mice or humans lacking ClC-7 or Ostm1 display osteopetrosis and lysosomal storage disease. Disruption of the endosomal ClC-5 Cl(-)/H(+)-exchanger leads to proteinuria and Dent's disease. Mouse models in which ClC-5 or ClC-7 is converted to uncoupled Cl(-) conductors suggest an important role of vesicular Cl(-) accumulation in these pathologies. The important functions of CLC Cl(-) channels were also revealed by human diseases and mouse models, with phenotypes including myotonia, renal loss of salt and water, deafness, blindness, leukodystrophy, and male infertility.
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Affiliation(s)
- Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie FMP and Max-Delbrück-Centrum für Molekulare Medizin MDC, Berlin, Germany
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55
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Skálová D, Zídková J, Voháňka S, Mazanec R, Mušová Z, Vondráček P, Mrázová L, Kraus J, Réblová K, Fajkusová L. CLCN1 mutations in Czech patients with myotonia congenita, in silico analysis of novel and known mutations in the human dimeric skeletal muscle chloride channel. PLoS One 2013; 8:e82549. [PMID: 24349310 PMCID: PMC3859631 DOI: 10.1371/journal.pone.0082549] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Accepted: 10/26/2013] [Indexed: 11/18/2022] Open
Abstract
Myotonia congenita (MC) is a genetic disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1) encoding the skeletal muscle chloride channel (ClC-1). Mutations of CLCN1 result in either autosomal dominant MC (Thomsen disease) or autosomal recessive MC (Becker disease). The ClC-1 protein is a homodimer with a separate ion pore within each monomer. Mutations causing recessive myotonia most likely affect properties of only the mutant monomer in the heterodimer, leaving the wild type monomer unaffected, while mutations causing dominant myotonia affect properties of both subunits in the heterodimer. Our study addresses two points: 1) molecular genetic diagnostics of MC by analysis of the CLCN1 gene and 2) structural analysis of mutations in the homology model of the human dimeric ClC-1 protein. In the first part, 34 different types of CLCN1 mutations were identified in 51 MC probands (14 mutations were new). In the second part, on the basis of the homology model we identified the amino acids which forming the dimer interface and those which form the Cl(-) ion pathway. In the literature, we searched for mutations of these amino acids for which functional analyses were performed to assess the correlation between localisation of a mutation and occurrence of a dominant-negative effect (corresponding to dominant MC). This revealed that both types of mutations, with and without a dominant-negative effect, are localised at the dimer interface while solely mutations without a dominant-negative effect occur inside the chloride channel. This work is complemented by structural analysis of the homology model which provides elucidation of the effects of mutations, including a description of impacts of newly detected missense mutations.
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Affiliation(s)
- Daniela Skálová
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Jana Zídková
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Stanislav Voháňka
- Department of Neurology, University Hospital Brno, Brno, Czech Republic
| | - Radim Mazanec
- Department of Neurology, Charles University Second Faculty of Medicine and University Hospital Motol, Prague, Czech Republic
| | - Zuzana Mušová
- Department of Biology and Medical Genetics, Charles University Second Faculty of Medicine and University Hospital Motol, Prague, Czech Republic
| | - Petr Vondráček
- Department of Child Neurology, University Hospital Brno, Brno, Czech Republic
| | - Lenka Mrázová
- Department of Child Neurology, University Hospital Brno, Brno, Czech Republic
| | - Josef Kraus
- Department of Child Neurology, Second School of Medicine, Charles University and University Hospital Motol, Prague, Czech Republic
| | - Kamila Réblová
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- * E-mail: (KR); (LF)
| | - Lenka Fajkusová
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- * E-mail: (KR); (LF)
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56
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Ereño-Orbea J, Oyenarte I, Martínez-Cruz LA. CBS domains: Ligand binding sites and conformational variability. Arch Biochem Biophys 2013; 540:70-81. [DOI: 10.1016/j.abb.2013.10.008] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 10/08/2013] [Accepted: 10/11/2013] [Indexed: 02/07/2023]
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57
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Yamada T, Bhate MP, Strange K. Regulatory phosphorylation induces extracellular conformational changes in a CLC anion channel. Biophys J 2013; 104:1893-904. [PMID: 23663832 DOI: 10.1016/j.bpj.2013.03.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 03/15/2013] [Accepted: 03/19/2013] [Indexed: 10/26/2022] Open
Abstract
CLH-3b is a CLC-1/2/Ka/Kb channel homolog activated by meiotic cell cycle progression and cell swelling. Channel inhibition occurs by GCK-3 kinase-mediated phosphorylation of serine residues on the cytoplasmic C-terminus linker connecting CBS1 and CBS2. Two conserved aromatic amino acid residues located on the intracellular loop connecting membrane helices H and I and α1 of CBS2 are required for transducing phosphorylation changes into changes in channel activity. Helices H and I form part of the interface between the two subunits that comprise functional CLC channels. Using a cysteine-less CLH-3b mutant, we demonstrate that the sulfhydryl reagent reactivity of substituted cysteines at the subunit interface changes dramatically during GCK-3-mediated channel inhibition and that these changes are prevented by mutation of the H-I loop/CBS2 α1 signal transduction domain. We also show that GCK-3 modifies Zn(2+) inhibition, which is thought to be mediated by the common gating process. These and other results suggest that phosphorylation of the cytoplasmic C-terminus inhibits CLH-3b by inducing subunit interface conformation changes that activate the common gate. Our findings have important implications for understanding CLC regulation by diverse signaling mechanisms and for understanding the structure/function relationships that mediate intraprotein communication in this important family of Cl(-) transport proteins.
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Affiliation(s)
- Toshiki Yamada
- Boylan Center for Cellular and Molecular Physiology, Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, USA
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58
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CLCNKB mutations causing mild Bartter syndrome profoundly alter the pH and Ca2+ dependence of ClC-Kb channels. Pflugers Arch 2013; 466:1713-23. [DOI: 10.1007/s00424-013-1401-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 10/30/2013] [Accepted: 11/01/2013] [Indexed: 10/26/2022]
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59
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Molecular determinants of common gating of a ClC chloride channel. Nat Commun 2013; 4:2507. [DOI: 10.1038/ncomms3507] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 08/27/2013] [Indexed: 11/08/2022] Open
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60
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Martinez-Martinez P, Molenaar PC, Losen M, Stevens J, Baets MHD, Szoke A, Honnorat J, Tamouza R, Leboyer M, Os JV, Rutten BPF. Autoantibodies to neurotransmitter receptors and ion channels: from neuromuscular to neuropsychiatric disorders. Front Genet 2013; 4:181. [PMID: 24065983 PMCID: PMC3778371 DOI: 10.3389/fgene.2013.00181] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 08/27/2013] [Indexed: 01/17/2023] Open
Abstract
Changes of voltage-gated ion channels and ligand-gated receptor channels caused by mutation or autoimmune attack are the cause of so-called channelopathies in the central and peripheral nervous system. We present the pathophysiology of channelopathies of the neuromuscular junction in terms of loss-of-function and gain-of-function principles. Autoantibodies generally have reduced access to the central nervous system, but in some cases this is enough to cause disease. A review is provided of recent findings implicating autoantibodies against ligand-activated receptor channels and potassium channels in psychiatric and neurological disorders, including schizophrenia and limbic encephalitis. The emergence of channelopathy-related neuropsychiatric disorders has implications for research and practice.
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Affiliation(s)
- Pilar Martinez-Martinez
- Department of Psychiatry and Psychology, School for Mental Health and Neuroscience, Maastricht University Maastricht, Netherlands
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61
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Bandschapp O, Iaizzo PA. Pathophysiologic and anesthetic considerations for patients with myotonia congenita or periodic paralyses. Paediatr Anaesth 2013; 23:824-33. [PMID: 23802937 DOI: 10.1111/pan.12217] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 05/29/2013] [Indexed: 12/13/2022]
Abstract
Myotonia congenita and periodic paralyses are hereditary skeletal muscle channelopathies. In these disorders, various channel defects in the sarcolemma lead to a severely disturbed membrane excitability of the affected skeletal muscles. The clinical picture can range from severe myotonic reactions (e.g., masseter spasm, opisthotonus) to attacks of weakness and paralysis. Provided here is a short overview of the pathomechanisms behind such wide-ranging phenotypic presentations in these patients, followed by recommendations concerning the management of anesthesia in such populations.
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Affiliation(s)
- Oliver Bandschapp
- Department of Anesthesia, Surgical Intensive Care, Prehospital Emergency Medicine and Pain Therapy, University Hospital Basel, Basel, Switzerland.
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62
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Takeda I, Takahashi T, Ueno H, Morino H, Ochi K, Nakamura T, Hosomi N, Kawakami H, Hashimoto K, Matsumoto M. Autosomal recessive Andersen-Tawil syndrome with a novel mutation L94P in Kir2.1. ACTA ACUST UNITED AC 2013. [DOI: 10.1111/ncn3.38] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ikuko Takeda
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Tetsuya Takahashi
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Hiroki Ueno
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Hiroyuki Morino
- Department of Epidemiology; Research Institute for Radiation Biology and Medicine; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Kazuhide Ochi
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Takeshi Nakamura
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Naohisa Hosomi
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Hideshi Kawakami
- Department of Epidemiology; Research Institute for Radiation Biology and Medicine; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Kouichi Hashimoto
- Department of Neurophysiology; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
| | - Masayasu Matsumoto
- Department of Clinical Neuroscience and Therapeutics; Hiroshima University; Graduate School of Biomedical and Health Sciences; Hiroshima; Japan
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63
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Functional characterization of ClC-1 mutations from patients affected by recessive myotonia congenita presenting with different clinical phenotypes. Exp Neurol 2013; 248:530-40. [PMID: 23933576 PMCID: PMC3781327 DOI: 10.1016/j.expneurol.2013.07.018] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 07/18/2013] [Accepted: 07/25/2013] [Indexed: 12/03/2022]
Abstract
Myotonia congenita (MC) is caused by loss-of-function mutations of the muscle ClC-1 chloride channel. Clinical manifestations include the variable association of myotonia and transitory weakness. We recently described a cohort of recessive MC patients showing, at a low rate repetitive nerves stimulation protocol, different values of compound muscle action potential (CMAP) transitory depression, which is considered the neurophysiologic counterpart of transitory weakness. From among this cohort, we studied the chloride currents generated by G190S (associated with pronounced transitory depression), F167L (little or no transitory depression), and A531V (variable transitory depression) hClC-1 mutants in transfected HEK293 cells using patch-clamp. While F167L had no effect on chloride currents, G190S dramatically shifts the voltage dependence of channel activation and A531V reduces channel expression. Such variability in molecular mechanisms observed in the hClC-1 mutants may help to explain the different clinical and neurophysiologic manifestations of each ClCN1 mutation. In addition we examined five different mutations found in compound heterozygosis with F167L, including the novel P558S, and we identified additional molecular defects. Finally, the G190S mutation appeared to impair acetazolamide effects on chloride currents in vitro. Myotonia congenita is a muscle disorder due to mutations in ClC-1 chloride channel. Eight ClC-1 channel mutants were studied using patch-clamp technique. Mutations induce a variety of molecular defects in ClC-1 channel function. We discuss the relationship between genotype and clinical phenotype.
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64
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Keck M, Andrini O, Lahuna O, Burgos J, Cid LP, Sepúlveda FV, L‘Hoste S, Blanchard A, Vargas-Poussou R, Lourdel S, Teulon J. NovelCLCNKBMutations Causing Bartter Syndrome Affect Channel Surface Expression. Hum Mutat 2013; 34:1269-78. [DOI: 10.1002/humu.22361] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 05/15/2013] [Indexed: 11/07/2022]
Affiliation(s)
- Mathilde Keck
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Olga Andrini
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Olivier Lahuna
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Johanna Burgos
- Centro de Estudios Científicos; Avenida Arturo Prat 514; Valdivia Chile
| | - L. Pablo Cid
- Centro de Estudios Científicos; Avenida Arturo Prat 514; Valdivia Chile
| | | | - Sébastien L‘Hoste
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Anne Blanchard
- Assistance Publique-Hôpitaux de Paris; Hôpital Européen Georges Pompidou; Centre d'Investigation Clinique; Paris France
- Université Paris-Descartes; Faculté de Médecine; Paris France
| | - Rosa Vargas-Poussou
- Université Paris-Descartes; Faculté de Médecine; Paris France
- Assistance Publique-Hôpitaux de Paris; Hôpital Européen Georges Pompidou; département de génétique; Paris France
| | - Stéphane Lourdel
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Jacques Teulon
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
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65
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A large cohort of myotonia congenita probands: novel mutations and a high-frequency mutation region in exons 4 and 5 of the CLCN1 gene. J Hum Genet 2013; 58:581-7. [DOI: 10.1038/jhg.2013.58] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Revised: 04/30/2013] [Accepted: 05/01/2013] [Indexed: 11/08/2022]
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66
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Rush ET, Stevens JM, Sanger WG, Olney AH. Report of a patient with developmental delay, hearing loss, growth retardation, and cleft lip and palate and a deletion of 7q34-36.1: review of distal 7q deletions. Am J Med Genet A 2013; 161A:1726-32. [PMID: 23696251 DOI: 10.1002/ajmg.a.35951] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 02/09/2013] [Indexed: 11/10/2022]
Abstract
The use of aCGH has improved our ability to find subtle cytogenetic abnormalities as well as to find more precise information in patients with previously known abnormalities. In addition, it has allowed more specific genotype-phenotype correlation. In this report we describe a patient with a chromosomal deletion initially diagnosed with conventional cytogenetic analysis which was redemonstrated and more specifically described upon aCGH analysis. Our patient is a 12-year-old female born to a 26-year-old G1P0 mother. She was noted as a neonate to have a bilateral cleft lip and cleft palate, abnormal external ears, dysmorphic facies, and moderate to severe hearing loss. She has subsequently shown developmental delay, hyperreflexia, seizures, hyperactivity, and absence of speech. Chromosomal analysis showed deletion of 7q34q36.1. FISH studies confirmed the deletion was interstitial. Parental chromosomes were performed and did not show any cytogenetic abnormalities. aCGH was recently performed for the patient to further characterize the breakpoints of the deletion and confirmed the deletion was interstitial and of 13.2 Mb in size. Both proximal and terminal 7q deletion show a different phenotype than that of our patient. A number of patients with similar deletions have been found and while significant variability is observed, a number of findings appear to be common to deletions in this region. Therefore, we feel that distal interstitial deletions of chromosome 7q represent a recognizable phenotype and could be considered a separate deletion syndrome.
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Affiliation(s)
- Eric T Rush
- Munroe-Meyer Institute for Genetics and Rehabilitation, University of Nebraska Medical Center, Omaha, NE, USA.
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67
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Jeong BC, Park SH, Yoo KS, Shin JS, Song HK. Change in single cystathionine β-synthase domain-containing protein from a bent to flat conformation upon adenosine monophosphate binding. J Struct Biol 2013; 183:40-6. [PMID: 23664870 DOI: 10.1016/j.jsb.2013.04.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 04/25/2013] [Accepted: 04/28/2013] [Indexed: 12/25/2022]
Abstract
Cystathionine β-synthase (CBS) domains are small intracellular modules that can act as binding domains for adenosine derivatives, and they may regulate the activity of associated enzymes or other functional domains. Among these, the single CBS domain-containing proteins, CBSXs, from Arabidopsis thaliana, have recently been identified as redox regulators of the thioredoxin system. Here, the crystal structure of CBSX2 in complex with adenosine monophosphate (AMP) is reported at 2.2Å resolution. The structure of dimeric CBSX2 with bound-AMP is shown to be approximately flat, which is in stark contrast to the bent form of apo-CBSXs. This conformational change in quaternary structure is triggered by a local structural change of the unique α5 helix, and by moving each loop P into an open conformation to accommodate incoming ligands. Furthermore, subtle rearrangement of the dimer interface triggers movement of all subunits, and consequently, the bent structure of the CBSX2 dimer becomes a flat structure. This reshaping of the structure upon complex formation with adenosine-containing ligand provides evidence that ligand-induced conformational reorganization of antiparallel CBS domains is an important regulatory mechanism.
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Affiliation(s)
- Byung-Cheon Jeong
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, South Korea
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68
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Heatwole CR, Statland JM, Logigian EL. The diagnosis and treatment of myotonic disorders. Muscle Nerve 2013; 47:632-48. [PMID: 23536309 DOI: 10.1002/mus.23683] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/14/2012] [Indexed: 12/12/2022]
Abstract
Myotonia is a defining clinical symptom and sign common to a relatively small group of muscle diseases, including the myotonic dystrophies and the nondystrophic myotonic disorders. Myotonia can be observed on clinical examination, as can its electrical correlate, myotonic discharges, on electrodiagnostic testing. Research interest in the myotonic disorders continues to expand rapidly, which justifies a review of the scientific bases, clinical manifestations, and numerous therapeutic approaches associated with these disorders. We review the pathomechanisms of myotonia, the clinical features of the dystrophic and nondystrophic myotonic disorders, and the diagnostic approach and treatment options for patients with symptomatic myotonia.
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Affiliation(s)
- Chad R Heatwole
- Department of Neurology, Box 673, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, New York, New York 14642, USA.
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69
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Lee TT, Zhang XD, Chuang CC, Chen JJ, Chen YA, Chen SC, Chen TY, Tang CY. Myotonia congenita mutation enhances the degradation of human CLC-1 chloride channels. PLoS One 2013; 8:e55930. [PMID: 23424641 PMCID: PMC3570542 DOI: 10.1371/journal.pone.0055930] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 01/03/2013] [Indexed: 11/18/2022] Open
Abstract
Myotonia congenita is a hereditary muscle disorder caused by mutations in the human voltage-gated chloride (Cl−) channel CLC-1. Myotonia congenita can be inherited in an autosomal recessive (Becker type) or dominant (Thomsen type) fashion. One hypothesis for myotonia congenita is that the inheritance pattern of the disease is determined by the functional consequence of the mutation on the gating of CLC-1 channels. Several disease-related mutations, however, have been shown to yield functional CLC-1 channels with no detectable gating defects. In this study, we have functionally and biochemically characterized a myotonia mutant: A531V. Despite a gating property similar to that of wild-type (WT) channels, the mutant CLC-1 channel displayed a diminished whole-cell current density and a reduction in the total protein expression level. Our biochemical analyses further demonstrated that the reduced expression of A531V can be largely attributed to an enhanced proteasomal degradation as well as a defect in protein trafficking to surface membranes. Moreover, the A531V mutant protein also appeared to be associated with excessive endosomal-lysosomal degradation. Neither the reduced protein expression nor the diminished current density was rescued by incubating A531V-expressing cells at 27°C. These results demonstrate that the molecular pathophysiology of A531V does not involve anomalous channel gating, but rather a disruption of the balance between the synthesis and degradation of the CLC-1 channel protein.
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Affiliation(s)
- Ting-Ting Lee
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Xiao-Dong Zhang
- Neuroscience Center, University of California Davis, Davis, California, United States of America
| | - Chao-Chin Chuang
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Jing-Jer Chen
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Yi-An Chen
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Shu-Ching Chen
- Department of Medical Research, National Taiwan University Hospital, Taipei, Taiwan
| | - Tsung-Yu Chen
- Neuroscience Center, University of California Davis, Davis, California, United States of America
| | - Chih-Yung Tang
- Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan
- Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan
- * E-mail:
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70
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Jeong BC, Park SH, Yoo KS, Shin JS, Song HK. Crystal structure of the single cystathionine β-synthase domain-containing protein CBSX1 from Arabidopsis thaliana. Biochem Biophys Res Commun 2012; 430:265-71. [PMID: 23159611 DOI: 10.1016/j.bbrc.2012.10.139] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Accepted: 10/31/2012] [Indexed: 01/28/2023]
Abstract
The single cystathionine β-synthase (CBS) pair proteins from Arabidopsis thaliana have been identified as being a redox regulator of the thioredoxin (Trx) system. CBSX1 and CBSX2, which are two of the six Arabidopsis cystathione β-synthase domain-containing proteins that contain only a single CBS pair, have close sequence similarity. Recently, the crystal structure of CBSX2 was determined and a significant portion of the internal region was disordered. In this study, crystal structures of full-length CBSX1 and the internal loop deleted (Δloop) form are reported at resolutions of 2.4 and 2.2Å, respectively. The structures of CBSX1 show that they form anti-parallel dimers along their central twofold axis and have a unique ∼155° bend along the side. This is different from the angle of CBSX2, which is suggestive of the flexible nature of the relative angle between the monomers. The biochemical data that were obtained using the deletion as well as point mutants of CBSX1 confirmed the importance of AMP-ligand binding in terms of enhancing Trx activity.
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Affiliation(s)
- Byung-Cheon Jeong
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Republic of Korea
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71
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Miyazaki H, Yamada T, Parton A, Morrison R, Kim S, Beth AH, Strange K. CLC anion channel regulatory phosphorylation and conserved signal transduction domains. Biophys J 2012; 103:1706-18. [PMID: 23083714 DOI: 10.1016/j.bpj.2012.09.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 08/20/2012] [Accepted: 09/04/2012] [Indexed: 12/01/2022] Open
Abstract
The signaling mechanisms that regulate CLC anion channels are poorly understood. Caenorhabditis elegans CLH-3b is a member of the CLC-1/2/Ka/Kb channel subfamily. CLH-3b is activated by meiotic cell-cycle progression and cell swelling. Inhibition is brought about by GCK-3 kinase-mediated phosphorylation of S742 and S747 located on a ∼176 amino acid disordered domain linking CBS1 and CBS2. Much of the inter-CBS linker is dispensable for channel regulation. However, deletion of a 14 amino acid activation domain encompassing S742 and S747 inhibits channel activity to the same extent as GCK-3. The crystal structure of CmCLC demonstrated that CBS2 interfaces extensively with an intracellular loop connecting membrane helices H and I, the C-terminus of helix D, and a short linker connecting helix R to CBS1. Point mutagenesis of this interface identified two highly conserved aromatic amino acid residues located in the H-I loop and the first α-helix (α1) of CBS2. Mutation of either residue to alanine rendered CLH-3b insensitive to GCK-3 inhibition. We suggest that the dephosphorylated activation domain normally interacts with CBS1 and/or CBS2, and that conformational information associated with this interaction is transduced through a conserved signal transduction module comprising the H-I loop and CBS2 α1.
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Affiliation(s)
- Hiroaki Miyazaki
- Boylan Center for Cellular and Molecular Physiology, Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, USA
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72
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Guo WT, Xu WY, Gu MM. [Nonsense-mediated mRNA decay and human monogenic disease]. YI CHUAN = HEREDITAS 2012; 34:935-42. [PMID: 22917898 DOI: 10.3724/sp.j.1005.2012.00935] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Nonsense-mediated mRNA decay (NMD) is a widespread quality control mechanism in eukaryotic cells. It can recognize and degrade aberrant transcripts harbouring a premature translational termination codon (PTC), and thereby prevent the production of C-terminally truncated proteins which might be deleterious. Approximately, 30% of human genetic diseases are caused by transcripts containing PTCs. These transcripts are potential targets of NMD. As for monogenic diseases, NMD has effects on the phenotype or mode of inheritance. Here, we explain the mechanism of this surveillance pathway, and take several neuromuscular disorders as examples to discuss its influence for human monogenic diseases. The deeper understanding for NMD will shed light on the nosogenesis and therapies of monogenic diseases.
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Affiliation(s)
- Wen-Ting Guo
- Department of Medical Genetics, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
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73
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Richman DP, Yu Y, Lee TT, Tseng PY, Yu WP, Maselli RA, Tang CY, Chen TY. Dominantly inherited myotonia congenita resulting from a mutation that increases open probability of the muscle chloride channel CLC-1. Neuromolecular Med 2012; 14:328-37. [PMID: 22790975 DOI: 10.1007/s12017-012-8190-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 06/22/2012] [Indexed: 10/28/2022]
Abstract
Myotonia congenita-inducing mutations in the muscle chloride channel CLC-1 normally result in reduced open probability (P (o)) of this channel. One well-accepted mechanism of the dominant inheritance of this disease involves a dominant-negative effect of the mutation on the function of the common-gate of this homodimeric, double-barreled molecule. We report here a family with myotonia congenita characterized by muscle stiffness and clinical and electrophysiologic myotonic phenomena transmitted in an autosomal dominant pattern. DNA sequencing of DMPK and ZNF9 genes for myotonic muscular dystrophy types I and II was normal, whereas sequencing of CLC-1 encoding gene, CLCN1, identified a single heterozygous missense mutation, G233S. Patch-clamp analyses of this mutant CLC-1 channel in Xenopus oocytes revealed an increased P (o) of the channel's fast-gate, from ~0.4 in the wild type to >0.9 in the mutant at -90 mV. In contrast, the mutant exhibits a minimal effect on the P (o) of the common-gate. These results are consistent with the structural prediction that the mutation site is adjacent to the fast-gate of the channel. Overall, the mutant could lead to a significantly reduced dynamic response of CLC-1 to membrane depolarization, from a fivefold increase in chloride conductance in the wild type to a twofold increase in the mutant-this might result in slower membrane repolarization during an action potential. Since expression levels of the mutant and wild-type subunits in artificial model cell systems were unable to explain the disease symptoms, the mechanism leading to dominant inheritance in this family remains to be determined.
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Affiliation(s)
- David P Richman
- Department of Neurology and Center for Neuroscience, University of California, Davis, CA 95616, USA.
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74
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The Effects of the KCNQ Openers Retigabine and Flupirtine on Myotonia in Mammalian Skeletal Muscle Induced by a Chloride Channel Blocker. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2012; 2012:803082. [PMID: 22536291 PMCID: PMC3320144 DOI: 10.1155/2012/803082] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 01/12/2012] [Indexed: 12/19/2022]
Abstract
The purpose of this study was to investigate the effect of KCNQ (potassium channel, voltage-gated, KQT-like subfamily) openers in preventing myotonia caused by anthracene-9-carboxylic acid (9-AC, a chloride channel blocker). An animal model of myotonia can be elicited in murine skeletal muscle by 9-AC treatment. KCNQ openers, such as retigabine and flupirtine, can inhibit the increased twitch amplitude (0.1 Hz stimulation) and reduce the tetanic fade (20 Hz stimulations) observed in the presence of 9-AC. Furthermore, the prolonged twitch duration of skeletal muscle was also inhibited by retigabine or flupirtine. Lamotrigine (an anticonvulsant drug) has a lesser effect on the muscle twitch amplitude, tetanic fade, and prolonged twitch duration as compared with KCNQ openers. In experiments using intracellular recordings, retigabine and flupirtine clearly reduced the firing frequencies of repetitive action potentials induced by 9-AC. These data suggested that KCNQ openers prevent the myotonia induced by 9-AC, at least partly through enhancing potassium conductance in skeletal muscle. Taken together, these results indicate that KCNQ openers are potential alternative therapeutic agents for the treatment of myotonia.
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75
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Co-segregation of DM2 with a recessive CLCN1 mutation in juvenile onset of myotonic dystrophy type 2. J Neurol 2012; 259:2090-9. [DOI: 10.1007/s00415-012-6462-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2011] [Revised: 02/13/2012] [Accepted: 02/16/2012] [Indexed: 01/04/2023]
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76
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Mazón MJ, Barros F, De la Peña P, Quesada JF, Escudero A, Cobo AM, Pascual-Pascual SI, Gutiérrez-Rivas E, Guillén E, Arpa J, Eraso P, Portillo F, Molano J. Screening for mutations in Spanish families with myotonia. Functional analysis of novel mutations in CLCN1 gene. Neuromuscul Disord 2012; 22:231-43. [DOI: 10.1016/j.nmd.2011.10.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2011] [Revised: 10/09/2011] [Accepted: 10/13/2011] [Indexed: 11/28/2022]
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77
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Physiology and pathophysiology of CLC-1: mechanisms of a chloride channel disease, myotonia. J Biomed Biotechnol 2011; 2011:685328. [PMID: 22187529 PMCID: PMC3237021 DOI: 10.1155/2011/685328] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 07/18/2011] [Accepted: 09/10/2011] [Indexed: 12/22/2022] Open
Abstract
The CLC-1 chloride channel, a member of the CLC-channel/transporter family, plays important roles for the physiological functions of skeletal muscles. The opening of this chloride channel is voltage dependent and is also regulated by protons and chloride ions. Mutations of the gene encoding CLC-1 result in a genetic disease, myotonia congenita, which can be inherited as an autosmal dominant (Thomsen type) or an autosomal recessive (Becker type) pattern. These mutations are scattered throughout the entire protein sequence, and no clear relationship exists between the inheritance pattern of the mutation and the location of the mutation in the channel protein. The inheritance pattern of some but not all myotonia mutants can be explained by a working hypothesis that these mutations may exert a “dominant negative” effect on the gating function of the channel. However, other mutations may be due to different pathophysiological mechanisms, such as the defect of protein trafficking to membranes. Thus, the underlying mechanisms of myotonia are likely to be quite diverse, and elucidating the pathophysiology of myotonia mutations will require the understanding of multiple molecular/cellular mechanisms of CLC-1 channels in skeletal muscles, including molecular operation, protein synthesis, and membrane trafficking mechanisms.
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78
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Yoo KS, Ok SH, Jeong BC, Jung KW, Cui MH, Hyoung S, Lee MR, Song HK, Shin JS. Single cystathionine β-synthase domain-containing proteins modulate development by regulating the thioredoxin system in Arabidopsis. THE PLANT CELL 2011; 23:3577-94. [PMID: 22021414 PMCID: PMC3229136 DOI: 10.1105/tpc.111.089847] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 08/30/2011] [Accepted: 10/03/2011] [Indexed: 05/20/2023]
Abstract
Plant thioredoxins (Trxs) participate in two redox systems found in different cellular compartments: the NADP-Trx system (NTS) in the cytosol and mitochondria and the ferredoxin-Trx system (FTS) in the chloroplast, where they function as redox regulators by regulating the activity of various target enzymes. The identities of the master regulators that maintain cellular homeostasis and modulate timed development through redox regulating systems have remained completely unknown. Here, we show that proteins consisting of a single cystathionine β-synthase (CBS) domain pair stabilize cellular redox homeostasis and modulate plant development via regulation of Trx systems by sensing changes in adenosine-containing ligands. We identified two CBS domain-containing proteins in Arabidopsis thaliana, CBSX1 and CBSX2, which are localized to the chloroplast, where they activate all four Trxs in the FTS. CBSX3 was found to regulate mitochondrial Trx members in the NTS. CBSX1 directly regulates Trxs and thereby controls H(2)O(2) levels and regulates lignin polymerization in the anther endothecium. It also affects plant growth by regulating photosynthesis-related [corrected] enzymes, such as malate dehydrogenase, via homeostatic regulation of Trxs. Based on our findings, we suggest that the CBSX proteins (or a CBS pair) are ubiquitous redox regulators that regulate Trxs in the FTS and NTS to modulate development and maintain homeostasis under conditions that are threatening to the cell.
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Affiliation(s)
- Kyoung Shin Yoo
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea.
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79
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van Lunteren E, Moyer M, Cooperrider J, Pollarine J. Impaired Wheel Running Exercise in CLC-1 Chloride Channel-Deficient Myotonic Mice. Front Physiol 2011; 2:47. [PMID: 21886624 PMCID: PMC3152724 DOI: 10.3389/fphys.2011.00047] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2011] [Accepted: 07/25/2011] [Indexed: 11/13/2022] Open
Abstract
Background: Genetic deficiency of the muscle CLC-1 chloride channel leads to myotonia, which is manifested most prominently by slowing of muscle relaxation. Humans experience this as muscle stiffness upon initiation of contraction, although this can be overcome with repeated efforts (the “warm-up” phenomenon). The extent to which CLC-1 deficiency impairs exercise activity is controversial. We hypothesized that skeletal muscle CLC-1 chloride channel deficiency leads to severe reductions in spontaneous exercise. Methodology/Principal Findings: To examine this quantitatively, myotonic CLC-1 deficient mice were provided access to running wheels, and their spontaneous running activity was quantified subsequently. Differences between myotonic and normal mice in running were not present soon after introduction to the running wheels, but were fully established during week 2. During the eighth week, myotonic mice were running significantly less than normal mice (322 ± 177 vs 5058 ± 1253 m/day, P = 0.025). Furthermore, there were considerable reductions in consecutive running times (18.8 ± 1.5 vs 59.0 ± 3.7 min, P < 0.001) and in the distance per consecutive running period (58 ± 38 vs 601 ± 174 m, P = 0.048) in myotonic compared with normal animals. Conclusion/Significance: These findings indicate that CLC-1 chloride deficient myotonia in mice markedly impairs spontaneous exercise activity, with reductions in both total distance and consecutive running times.
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Affiliation(s)
- Erik van Lunteren
- Cleveland Department of Veterans Affairs Medical Center Cleveland, OH, USA
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80
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Pedersen TH, L-H Huang C, Fraser JA. An analysis of the relationships between subthreshold electrical properties and excitability in skeletal muscle. ACTA ACUST UNITED AC 2011; 138:73-93. [PMID: 21670208 PMCID: PMC3135320 DOI: 10.1085/jgp.201010510] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Skeletal muscle activation requires action potential (AP) initiation followed by its sarcolemmal propagation and tubular excitation to trigger Ca2+ release and contraction. Recent studies demonstrate that ion channels underlying the resting membrane conductance (GM) of fast-twitch mammalian muscle fibers are highly regulated during muscle activity. Thus, onset of activity reduces GM, whereas prolonged activity can markedly elevate GM. Although these observations implicate GM regulation in control of muscle excitability, classical theoretical studies in un-myelinated axons predict little influence of GM on membrane excitability. However, surface membrane morphologies differ markedly between un-myelinated axons and muscle fibers, predominantly because of the tubular (t)-system of muscle fibers. This study develops a linear circuit model of mammalian muscle fiber and uses this to assess the role of subthreshold electrical properties, including GM changes during muscle activity, for AP initiation, AP propagation, and t-system excitation. Experimental observations of frequency-dependent length constant and membrane-phase properties in fast-twitch rat fibers could only be replicated by models that included t-system luminal resistances. Having quantified these resistances, the resulting models showed enhanced conduction velocity of passive current flow also implicating elevated AP propagation velocity. Furthermore, the resistances filter passive currents such that higher frequency current components would determine sarcolemma AP conduction velocity, whereas lower frequency components excite t-system APs. Because GM modulation affects only the low-frequency membrane impedance, the GM changes in active muscle would predominantly affect neuromuscular transmission and low-frequency t-system excitation while exerting little influence on the high-frequency process of sarcolemmal AP propagation. This physiological role of GM regulation was increased by high Cl− permeability, as in muscle endplate regions, and by increased extracellular [K+], as observed in working muscle. Thus, reduced GM at the onset of exercise would enhance t-system excitation and neuromuscular transmission, whereas elevated GM after sustained activity would inhibit these processes and thereby accentuate muscle fatigue.
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Affiliation(s)
- Thomas H Pedersen
- Physiological Laboratory, University of Cambridge, England, UK. thp@-fi.au.dk
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81
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A CLCN1 mutation in dominant myotonia congenita impairs the increment of chloride conductance during repetitive depolarization. Neurosci Lett 2011; 494:155-60. [DOI: 10.1016/j.neulet.2011.03.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 02/28/2011] [Accepted: 03/01/2011] [Indexed: 11/22/2022]
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82
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Abstract
Neuromuscular diseases (NMD) constitute a group of phenotypically and genetically heterogeneous disorders, characterized by (progressive) weakness and atrophy of proximal and/or distal muscles. The objective of molecular testing is to confirm the pathogenicity of a relevant sequence variation by correlating an individual's phenotype with what is expected in a given condition. Within the last two decades the application of molecular genetic strategies has led to a delineation of subgroups of clinically indistinguishable NMDs and has disclosed marked disease overlap. The expanding number of molecular defined NMDs requires new strategies to classify overlapping and clinical indistinguishable phenotypes.
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Affiliation(s)
- Andrew Gomez-Vargas
- Department of Medicine, McMaster University, 1200 Main Street West, HSC 2H22, Hamilton, ON, Canada L8 N 3Z5
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83
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van Lunteren E, Spiegler SE, Moyer M. Fatigue-inducing stimulation resolves myotonia in a drug-induced model. BMC PHYSIOLOGY 2011; 11:5. [PMID: 21356096 PMCID: PMC3052176 DOI: 10.1186/1472-6793-11-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Accepted: 02/28/2011] [Indexed: 11/29/2022]
Abstract
Background Slowed muscle relaxation is the contractile hallmark of myotonia congenita, a disease caused by genetic CLC-1 chloride channel deficiency, which improves with antecedent brief contractions ("warm-up phenomenon"). It is unclear to what extent the myotonia continues to dissipate during continued repetitive contractions and how this relates temporally to muscle fatigue. Diaphragm, EDL, and soleus muscles were examined in vitro during repetitive 20 Hz and 50 Hz train stimulation in a drug-induced (9-AC) rat myotonia model. Results At the onset of stimulation, 9-AC treated diaphragm and EDL muscle had markedly prolonged half relaxation and late relaxation times (range 147 to 884 ms, 894 to 1324 ms). Half relaxation and late relaxation times reached near-normal values over the 5-10 and 10-40 subsequent contractions, respectively. In both muscles myotonia declined faster during repetitive 50 Hz than 20 Hz stimulation, and much faster than the rate of force loss during fatigue at both frequencies. Soleus muscle was resistant to the myotonic effects of 9-AC. Conclusions In a drug-induced model of mechanical myotonia, fatigue-inducing stimulation resolves the myotonia, which furthermore appears to be independent from the development of muscle fatigue.
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Affiliation(s)
- Erik van Lunteren
- Pulmonary and Critical Care Medicine, Case Western Reserve University and Louis Stokes Cleveland Department of Veterans Affairs, Cleveland, OH 44106, USA.
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84
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DiFranco M, Herrera A, Vergara JL. Chloride currents from the transverse tubular system in adult mammalian skeletal muscle fibers. ACTA ACUST UNITED AC 2010; 137:21-41. [PMID: 21149546 PMCID: PMC3010054 DOI: 10.1085/jgp.201010496] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Chloride fluxes are the main contributors to the resting conductance of mammalian skeletal muscle fibers. ClC-1, the most abundant chloride channel isoform in this preparation, is believed to be responsible for this conductance. However, the actual distribution of ClC-1 channels between the surface and transverse tubular system (TTS) membranes has not been assessed in intact muscle fibers. To investigate this issue, we voltageclamped enzymatically dissociated short fibers using a two-microelectrode configuration and simultaneously recorded chloride currents (ICl) and di-8-ANEPPS fluorescence signals to assess membrane potential changes in the TTS. Experiments were conducted in conditions that blocked all but the chloride conductance. Fibers were equilibrated with 40 or 70 mM intracellular chloride to enhance the magnitude of inward ICl, and the specific ClC-1 blocker 9-ACA was used to eliminate these currents whenever necessary. Voltage-dependent di-8-ANEPPS signals and ICl acquired before (control) and after the addition of 9-ACA were comparatively assessed. Early after the onset of stimulus pulses, di-8-ANEPPS signals under control conditions were smaller than those recorded in the presence of 9-ACA. We defined as attenuation the normalized time-dependent difference between these signals. Attenuation was discovered to be ICl dependent since its magnitude varied in close correlation with the amplitude and time course of ICl. While the properties of ICl, and those of the attenuation seen in optical records, could be simultaneously predicted by model simulations when the chloride permeability (PCl) at the surface and TTS membranes were approximately equal, the model failed to explain the optical data if PCl was precluded from the TTS membranes. Since the ratio between the areas of TTS membranes and the sarcolemma is large in mammalian muscle fibers, our results demonstrate that a significant fraction of the experimentally recorded ICl arises from TTS contributions.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, University of California, Los Angeles, Geffen School of Medicine, Los Angeles, CA 90095, USa
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85
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Lueck JD, Rossi AE, Thornton CA, Campbell KP, Dirksen RT. Sarcolemmal-restricted localization of functional ClC-1 channels in mouse skeletal muscle. J Gen Physiol 2010; 136:597-613. [PMID: 21078869 PMCID: PMC2995150 DOI: 10.1085/jgp.201010526] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 10/26/2010] [Indexed: 02/01/2023] Open
Abstract
Skeletal muscle fibers exhibit a high resting chloride conductance primarily determined by ClC-1 chloride channels that stabilize the resting membrane potential during repetitive stimulation. Although the importance of ClC-1 channel activity in maintaining normal muscle excitability is well appreciated, the subcellular location of this conductance remains highly controversial. Using a three-pronged multidisciplinary approach, we determined the location of functional ClC-1 channels in adult mouse skeletal muscle. First, formamide-induced detubulation of single flexor digitorum brevis (FDB) muscle fibers from 15-16-day-old mice did not significantly alter macroscopic ClC-1 current magnitude (at -140 mV; -39.0 +/- 4.5 and -42.3 +/- 5.0 nA, respectively), deactivation kinetics, or voltage dependence of channel activation (V(1/2) was -61.0 +/- 1.7 and -64.5 +/- 2.8 mV; k was 20.5 ± 0.8 and 22.8 +/- 1.2 mV, respectively), despite a 33% reduction in cell capacitance (from 465 +/- 36 to 312 +/- 23 pF). In paired whole cell voltage clamp experiments, where ClC-1 activity was measured before and after detubulation in the same fiber, no reduction in ClC-1 activity was observed, despite an approximately 40 and 60% reduction in membrane capacitance in FDB fibers from 15-16-day-old and adult mice, respectively. Second, using immunofluorescence and confocal microscopy, native ClC-1 channels in adult mouse FDB fibers were localized within the sarcolemma, 90 degrees out of phase with double rows of dihydropyridine receptor immunostaining of the T-tubule system. Third, adenoviral-mediated expression of green fluorescent protein-tagged ClC-1 channels in adult skeletal muscle of a mouse model of myotonic dystrophy type 1 resulted in a significant reduction in myotonia and localization of channels to the sarcolemma. Collectively, these results demonstrate that the majority of functional ClC-1 channels localize to the sarcolemma and provide essential insight into the basis of myofiber excitability in normal and diseased skeletal muscle.
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Affiliation(s)
- John D. Lueck
- Department of Pharmacology and Physiology, and Department of Neurology, University of Rochester, Rochester, NY 14642
- Department of Molecular Physiology and Biophysics, Department of Internal Medicine, Department of Neurology, and Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52246
| | - Ann E. Rossi
- Department of Pharmacology and Physiology, and Department of Neurology, University of Rochester, Rochester, NY 14642
| | - Charles A. Thornton
- Department of Pharmacology and Physiology, and Department of Neurology, University of Rochester, Rochester, NY 14642
| | - Kevin P. Campbell
- Department of Molecular Physiology and Biophysics, Department of Internal Medicine, Department of Neurology, and Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52246
| | - Robert T. Dirksen
- Department of Pharmacology and Physiology, and Department of Neurology, University of Rochester, Rochester, NY 14642
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86
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Abstract
NMD (nonsense-mediated mRNA decay) belongs to the best-studied mRNA surveillance systems of the cell, limiting the synthesis of truncated and potentially harmful proteins on the one hand and playing an initially unexpected role in the regulation of global gene expression on the other hand. In the present review, we briefly discuss the factors involved in NMD, the different models proposed for the recognition of PTCs (premature termination codons), the diverse physiological roles of NMD, the involvement of this surveillance pathway in disease and the current strategies for medical treatment of PTC-related diseases.
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87
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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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88
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Dave S, Sheehan JH, Meiler J, Strange K. Unique gating properties of C. elegans ClC anion channel splice variants are determined by altered CBS domain conformation and the R-helix linker. Channels (Austin) 2010; 4:289-301. [PMID: 20581474 DOI: 10.4161/chan.4.4.12445] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
All eukaryotic and some prokaryotic ClC anion transport proteins have extensive cytoplasmic C-termini containing two cystathionine-β-synthase (CBS) domains. CBS domain secondary structure is highly conserved and consists of two α-helices and three β-strands arranged as β1-α1-β2-β3-α2. ClC CBS domain mutations cause muscle and bone disease and alter ClC gating. However, the precise functional roles of CBS domains and the structural bases by which they regulate ClC function are poorly understood. CLH-3a and CLH-3b are C. elegans ClC anion channel splice variants with strikingly different biophysical properties. Splice variation occurs at cytoplasmic N- and C-termini and includes several amino acids that form α2 of the second CBS domain (CBS2). We demonstrate that interchanging α2 between CLH-3a and CLH-3b interchanges their gating properties. The "R-helix" of ClC proteins forms part of the ion-conducting pore and selectivity filter and is connected to the cytoplasmic C-terminus via a short stretch of cytoplasmic amino acids termed the "R-helix linker". C-terminus conformation changes could cause R-helix structural rearrangements via this linker. X-ray structures of three ClC protein cytoplasmic C-termini suggest that α2 of CBS2 and the R-helix linker could be closely apposed and may therefore interact. We found that mutating apposing amino acids in α2 and the R-helix linker of CLH-3b was sufficient to give rise to CLH-3a-like gating. We postulate that the R-helix linker interacts with CBS2 α2, and that this putative interaction provides a pathway by which cytoplasmic C-terminus conformational changes induce conformational changes in membrane domains that in turn modulate ClC function.
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Affiliation(s)
- Sonya Dave
- Boylan Center for Cellular and Molecular Physiology, Mount Desert Island Biological Laboratory, Salisbury Cove, ME, USA
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89
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Bench-to-bedside review: Chloride in critical illness. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2010; 14:226. [PMID: 20663180 PMCID: PMC2945073 DOI: 10.1186/cc9052] [Citation(s) in RCA: 198] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Chloride is the principal anion in the extracellular fluid and is the second main contributor to plasma tonicity. Its concentration is frequently abnormal in intensive care unit patients, often as a consequence of fluid therapy. Yet chloride has received less attention than any other ion in the critical care literature. New insights into its physiological roles have emerged together with progress in understanding the structures and functions of chloride channels. In clinical practice, interest in a physicochemical approach to acid-base physiology has directed renewed attention to chloride as a major determinant of acid-base status. It has also indirectly helped to generate interest in other possible effects of disorders of chloraemia. The present review summarizes key aspects of chloride physiology, including its channels, as well as the clinical relevance of disorders of chloraemia. The paper also highlights current knowledge on the impact of different types of intravenous fluids on chloride concentration and the potential effects of such changes on organ physiology. Finally, the review examines the potential intensive care unit practice implications of a better understanding of chloride.
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90
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Accardi A, Picollo A. CLC channels and transporters: proteins with borderline personalities. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1457-64. [PMID: 20188062 DOI: 10.1016/j.bbamem.2010.02.022] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 02/12/2010] [Accepted: 02/18/2010] [Indexed: 11/19/2022]
Abstract
Controlled chloride movement across membranes is essential for a variety of physiological processes ranging from salt homeostasis in the kidneys to acidification of cellular compartments. The CLC family is formed by two, not so distinct, sub-classes of membrane transport proteins: Cl(-) channels and H(+)/Cl(-) exchangers. All CLC's are homodimers with each monomer forming an individual Cl- permeation pathway which appears to be largely unaltered in the two CLC sub-classes. Key residues for ion binding and selectivity are also highly conserved. Most CLC's have large cytosolic carboxy-terminal domains containing two cystathionine beta-synthetase (CBS) domains. The C-termini are critical regulators of protein trafficking and directly modulate Cl- by binding intracellular ATP, H+ or oxidizing compounds. This review focuses on the recent mechanistic insights on the how the structural similarities between CLC channels and transporters translate in unexpected mechanistic analogies between these two sub-classes.
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Affiliation(s)
- Alessio Accardi
- Department of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
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91
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Abstract
Mutations of voltage-gated ion channels cause several channelopathies of skeletal muscle, which present clinically with myotonia, periodic paralysis, or a combination of both. Expression studies have revealed both loss-of-function and gain-of-function defects for the currents passed by mutant channels. In many cases, these functional changes could be mechanistically linked to the defects of fibre excitability underlying myotonia or periodic paralysis. One remaining enigma was the basis for depolarization-induced weakness in hypokalaemic periodic paralysis (HypoPP) arising from mutations in either sodium or calcium channels. Curiously, 14 of 15 HypoPP mutations are at arginines in S4 voltage sensors, and recent observations show that these substitutions support an alternative pathway for ion conduction, the gating pore, that may be the source of the aberrant depolarization during an attack of paralysis.
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Affiliation(s)
- Stephen C Cannon
- Department of Neurology and Program in Neuroscience, 5323 Harry Hines Blvd, UT Southwestern Medical Center, Dallas, TX 75390-8813, USA.
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92
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Pedersen TH, de Paoli FV, de Paoli FV, Flatman JA, Nielsen OB. Regulation of ClC-1 and KATP channels in action potential-firing fast-twitch muscle fibers. ACTA ACUST UNITED AC 2010; 134:309-22. [PMID: 19786584 PMCID: PMC2757767 DOI: 10.1085/jgp.200910290] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Action potential (AP) excitation requires a transient dominance of depolarizing membrane currents over the repolarizing membrane currents that stabilize the resting membrane potential. Such stabilizing currents, in turn, depend on passive membrane conductance (G(m)), which in skeletal muscle fibers covers membrane conductances for K(+) (G(K)) and Cl(-) (G(Cl)). Myotonic disorders and studies with metabolically poisoned muscle have revealed capacities of G(K) and G(Cl) to inversely interfere with muscle excitability. However, whether regulation of G(K) and G(Cl) occur in AP-firing muscle under normal physiological conditions is unknown. This study establishes a technique that allows the determination of G(Cl) and G(K) with a temporal resolution of seconds in AP-firing muscle fibers. With this approach, we have identified and quantified a biphasic regulation of G(m) in active fast-twitch extensor digitorum longus fibers of the rat. Thus, at the onset of AP firing, a reduction in G(Cl) of approximately 70% caused G(m) to decline by approximately 55% in a manner that is well described by a single exponential function characterized by a time constant of approximately 200 APs (phase 1). When stimulation was continued beyond approximately 1,800 APs, synchronized elevations in G(K) ( approximately 14-fold) and G(Cl) ( approximately 3-fold) caused G(m) to rise sigmoidally to approximately 400% of its level before AP firing (phase 2). Phase 2 was often associated with a failure to excite APs. When AP firing was ceased during phase 2, G(m) recovered to its level before AP firing in approximately 1 min. Experiments with glibenclamide (K(ATP) channel inhibitor) and 9-anthracene carboxylic acid (ClC-1 Cl(-) channel inhibitor) revealed that the decreased G(m) during phase 1 reflected ClC-1 channel inhibition, whereas the massively elevated G(m) during phase 2 reflected synchronized openings of ClC-1 and K(ATP) channels. In conclusion, G(Cl) and G(K) are acutely regulated in AP-firing fast-twitch muscle fibers. Such regulation may contribute to the physiological control of excitability in active muscle.
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93
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ClC transporters: discoveries and challenges in defining the mechanisms underlying function and regulation of ClC-5. Pflugers Arch 2010; 460:543-57. [PMID: 20049483 DOI: 10.1007/s00424-009-0769-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 11/27/2009] [Accepted: 11/30/2009] [Indexed: 02/03/2023]
Abstract
The involvement of several members of the chloride channel (ClC) family of membrane proteins in human disease highlights the need to define the mechanisms underlying their function and the consequences of disease-causing mutations. Despite the utility of high-resolution structural models, our understanding of the molecular basis for function of the chloride channels and transporters in the family remains incomplete. In this review, we focus on recent discoveries regarding molecular mechanisms underlying the regulated chloride:proton antiporter activity of ClC-5, the protein mutated in the Dent's disease-a kidney disease presenting with proteinuria and renal failure in severe cases. We discuss the putative role of ClC-5 in receptor-mediated endocytosis and protein uptake by the proximal renal tubule and the possible molecular and cellular consequences of disease-causing mutations. However, validation of these models will require future study of the intrinsic function of this transporter, in situ, in the membranes of recycling endosomes in proximal tubule epithelial cells.
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94
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Binding of S-methyl-5'-thioadenosine and S-adenosyl-L-methionine to protein MJ0100 triggers an open-to-closed conformational change in its CBS motif pair. J Mol Biol 2009; 396:800-20. [PMID: 20026078 DOI: 10.1016/j.jmb.2009.12.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 12/09/2009] [Accepted: 12/09/2009] [Indexed: 02/03/2023]
Abstract
Cystathionine beta-synthase (CBS) domains are small motifs that are present in proteins with completely different functions. Several genetic diseases in humans have been associated with mutations in their sequence, which has made them promising targets for rational drug design. The protein MJ0100 from Methanocaldococcus jannaschii includes a DUF39 domain of so far unknown function and a CBS domain pair (Bateman domain) at its C-terminus. This work presents the crystallographic analysis of four different states of the CBS motif pair of MJ0100 in complex with different numbers of S-adenosyl-L-methionine (SAM) and S-methyl-5'-thioadenosine (MTA) ligands, providing evidence that ligand-induced conformational reorganization of Bateman domain dimers could be an important regulatory mechanism. These observations are in contrast to what is known from most of the other Bateman domain structures but are supported by recent studies on the magnesium transporter MgtE. Our structures represent the first example of a CBS domain protein complexed with SAM and/or MTA and might provide a structural basis for understanding the molecular mechanisms regulated by SAM upon binding to the C-terminal domain of human CBS, whose structure remains unknown.
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95
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Skeletal muscle channelopathies: new insights into the periodic paralyses and nondystrophic myotonias. Curr Opin Neurol 2009; 22:524-31. [PMID: 19571750 DOI: 10.1097/wco.0b013e32832efa8f] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE OF REVIEW To summarize advances in our understanding of the clinical phenotypes, genetics, and molecular pathophysiology of the periodic paralyses, the nondystrophic myotonias, and other muscle channelopathies. RECENT FINDINGS The number of pathogenic mutations causing periodic paralysis, nondystrophic myotonias, and ryanodinopathies continues to grow with the advent of exon hierarchy analysis strategies for genetic screening and better understanding and recognition of disease phenotypes. Recent studies have expanded and clarified the role of gating pore current in channelopathy pathogenesis. It has been shown that the gating pore current can account for the molecular and phenotypic diseases observed in the muscle sodium channelopathies, and, given that homologous residues are affected in mutations of calcium channels, it is possible that pore leak represents a pathomechanism applicable to many channel diseases. Improvements in treatment of the muscle channelopathies are on the horizon. A randomized controlled trial has been initiated for the study of mexiletine in nondystrophic myotonias. The class IC antiarrhythmia drug flecainide has been shown to depress ventricular ectopy and improve exercise capacity in patients with Andersen-Tawil syndrome. SUMMARY Recent studies have expanded our understanding of gating pore current as a disease-causing mechanism in the muscle channelopathies and have allowed new correlations to be drawn between disease genotype and phenotype.
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96
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Moon IS, Kim HS, Shin JH, Park YE, Park KH, Shin YB, Bae JS, Choi YC, Kim DS. Novel CLCN1 mutations and clinical features of Korean patients with myotonia congenita. J Korean Med Sci 2009; 24:1038-44. [PMID: 19949657 PMCID: PMC2775849 DOI: 10.3346/jkms.2009.24.6.1038] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Accepted: 07/22/2009] [Indexed: 11/20/2022] Open
Abstract
Myotonia congenita (MC) is a form of nondystrophic myotonia caused by a mutation of CLCN1, which encodes human skeletal muscle chloride channel (CLC-1). We performed sequence analysis of all coding regions of CLCN1 in patients clinically diagnosed with MC, and identified 10 unrelated Korean patients harboring mutations. Detailed clinical analysis was performed in these patients to identify their clinical characteristics in relation to their genotypes. The CLCN1 mutational analyses revealed nine different point mutations. Of these, six (p.M128I, p.S189C, p.M373L, p.P480S, p.G523D, and p.M609K) were novel and could be unique among Koreans. While some features including predominant lower extremity involvement and normal to slightly elevated creatine kinase levels were consistently observed, general clinical features were highly variable in terms of age of onset, clinical severity, aggravating factors, and response to treatment. Our study is the first systematic study of MC in Korea, and shows its expanding clinical and genetic spectrums.
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Affiliation(s)
- In-Soo Moon
- Department of Neurology, Dae-Dong Hospital, Busan, Korea
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Hyang-Sook Kim
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Jin-Hong Shin
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Yeong-Eun Park
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Kyu-Hyun Park
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Yong-Bum Shin
- Department of Rehabilitation Medicine, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Jong Seok Bae
- Department of Neurology, College of Medicine, Inje University, Busan, Korea
| | - Young-Chul Choi
- Department of Neurology, College of Medicine, Yonsei University, Seoul, Korea
| | - Dae-Seong Kim
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
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97
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Bashyam MD. Nonsense-mediated decay: linking a basic cellular process to human disease. Expert Rev Mol Diagn 2009; 9:299-303. [PMID: 19435450 DOI: 10.1586/erm.09.18] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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98
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Kino Y, Washizu C, Oma Y, Onishi H, Nezu Y, Sasagawa N, Nukina N, Ishiura S. MBNL and CELF proteins regulate alternative splicing of the skeletal muscle chloride channel CLCN1. Nucleic Acids Res 2009; 37:6477-90. [PMID: 19720736 PMCID: PMC2770659 DOI: 10.1093/nar/gkp681] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The expression and function of the skeletal muscle chloride channel CLCN1/ClC-1 is regulated by alternative splicing. Inclusion of the CLCN1 exon 7A is aberrantly elevated in myotonic dystrophy (DM), a genetic disorder caused by the expansion of a CTG or CCTG repeat. Increased exon 7A inclusion leads to a reduction in CLCN1 function, which can be causative of myotonia. Two RNA-binding protein families—muscleblind-like (MBNL) and CUG-BP and ETR-3-like factor (CELF) proteins—are thought to mediate the splicing misregulation in DM. Here, we have identified multiple factors that regulate the alternative splicing of a mouse Clcn1 minigene. The inclusion of exon 7A was repressed by MBNL proteins while promoted by an expanded CUG repeat or CELF4, but not by CUG-BP. Mutation analyses suggested that exon 7A and its flanking region mediate the effect of MBNL1, whereas another distinct region in intron 6 mediates that of CELF4. An exonic splicing enhancer essential for the inclusion of exon 7A was identified at the 5′ end of this exon, which might be inhibited by MBNL1. Collectively, these results provide a mechanistic model for the regulation of Clcn1 splicing, and reveal novel regulatory properties of MBNL and CELF proteins.
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Affiliation(s)
- Yoshihiro Kino
- Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Wako-shi, Saitama 351-0198, Japan
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99
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Gómez García I, Kortázar D, Oyenarte I, Mato JM, Martínez-Chantar ML, Martínez-Cruz LA. Purification, crystallization and preliminary crystallographic analysis of protein MJ1225 from Methanocaldococcus jannaschii, a putative archaeal homologue of gamma-AMPK. Acta Crystallogr Sect F Struct Biol Cryst Commun 2009; 65:813-7. [PMID: 19652347 PMCID: PMC2720341 DOI: 10.1107/s1744309109026475] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Accepted: 07/07/2009] [Indexed: 01/05/2023]
Abstract
In mammals, AMP-activated protein kinase (AMPK) is a heterotrimeric protein composed of a catalytic serine/threonine kinase subunit (alpha) and two regulatory subunits (beta and gamma). The gamma subunit senses the intracellular energy status by competitively binding AMP and ATP and is thought to be responsible for allosteric regulation of the whole complex. This work describes the purification and preliminary crystallographic analysis of protein MJ1225 from Methanocaldococcus jannaschii, an archaeal homologue of gamma-AMPK. The purified protein was crystallized using the hanging-drop vapour-diffusion method. Diffraction data for MJ1225 were collected to 2.3 A resolution using synchrotron radiation. The crystals belonged to space group H32, with unit-cell parameters a = b = 108.95, c = 148.08 A, alpha = beta = 90.00, gamma = 120.00 degrees . Preliminary analysis of the X-ray data indicated that there was one molecule per asymmetric unit.
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Affiliation(s)
- Inmaculada Gómez García
- Structural Biology Unit, CIC bioGUNE, Parque Tecnológico de Bizkaia, Edificio 800, 48160 Derio, Bizkaia, Spain
| | - Danel Kortázar
- Structural Biology Unit, CIC bioGUNE, Parque Tecnológico de Bizkaia, Edificio 800, 48160 Derio, Bizkaia, Spain
| | - Iker Oyenarte
- Structural Biology Unit, CIC bioGUNE, Parque Tecnológico de Bizkaia, Edificio 800, 48160 Derio, Bizkaia, Spain
| | - José María Mato
- Metabolomics Unit, CIC bioGUNE, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (Ciberedh), Parque Tecnológico de Bizkaia, Edificio 801, 48160 Derio Bizkaia, Spain
| | - María Luz Martínez-Chantar
- Metabolomics Unit, CIC bioGUNE, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (Ciberedh), Parque Tecnológico de Bizkaia, Edificio 801, 48160 Derio Bizkaia, Spain
| | - Luis Alfonso Martínez-Cruz
- Structural Biology Unit, CIC bioGUNE, Parque Tecnológico de Bizkaia, Edificio 800, 48160 Derio, Bizkaia, Spain
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100
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Muscle ultrasound measurements and functional muscle parameters in non-dystrophic myotonias suggest structural muscle changes. Neuromuscul Disord 2009; 19:462-7. [DOI: 10.1016/j.nmd.2009.06.369] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2009] [Revised: 05/18/2009] [Accepted: 06/03/2009] [Indexed: 12/13/2022]
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