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Djalali-Cuevas A, Rettel M, Stein F, Savitski M, Kearns S, Kelly J, Biggs M, Skoufos I, Tzora A, Prassinos N, Diakakis N, Zeugolis DI. Macromolecular crowding in human tenocyte and skin fibroblast cultures: A comparative analysis. Mater Today Bio 2024; 25:100977. [PMID: 38322661 PMCID: PMC10846491 DOI: 10.1016/j.mtbio.2024.100977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 12/22/2023] [Accepted: 01/24/2024] [Indexed: 02/08/2024] Open
Abstract
Although human tenocytes and dermal fibroblasts have shown promise in tendon engineering, no tissue engineered medicine has been developed due to the prolonged ex vivo time required to develop an implantable device. Considering that macromolecular crowding has the potential to substantially accelerate the development of functional tissue facsimiles, herein we compared human tenocyte and dermal fibroblast behaviour under standard and macromolecular crowding conditions to inform future studies in tendon engineering. Basic cell function analysis made apparent the innocuousness of macromolecular crowding for both cell types. Gene expression analysis of the without macromolecular crowding groups revealed expression of tendon related molecules in human dermal fibroblasts and tenocytes. Protein electrophoresis and immunocytochemistry analyses showed significantly increased and similar deposition of collagen fibres by macromolecular crowding in the two cell types. Proteomics analysis demonstrated great similarities between human tenocyte and dermal fibroblast cultures, as well as the induction of haemostatic, anti-microbial and tissue-protective proteins by macromolecular crowding in both cell populations. Collectively, these data rationalise the use of either human dermal fibroblasts or tenocytes in combination with macromolecular crowding in tendon engineering.
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Affiliation(s)
- Adrian Djalali-Cuevas
- Laboratory of Animal Science, Nutrition and Biotechnology, School of Agriculture, University of Ioannina, Arta, Greece
- School of Veterinary Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
- Regenerative, Modular & Developmental Engineering Laboratory (REMODEL), Charles Institute of Dermatology, Conway Institute of Biomolecular & Biomedical Research and School of Mechanical & Materials Engineering, University College Dublin (UCD), Dublin, Ireland
| | - Mandy Rettel
- Proteomics Core Facility, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Frank Stein
- Proteomics Core Facility, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Mikhail Savitski
- Proteomics Core Facility, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | | | - Jack Kelly
- Galway University Hospital, Galway, Ireland
| | - Manus Biggs
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, University of Galway, Galway, Ireland
| | - Ioannis Skoufos
- Laboratory of Animal Science, Nutrition and Biotechnology, School of Agriculture, University of Ioannina, Arta, Greece
| | - Athina Tzora
- Laboratory of Animal Science, Nutrition and Biotechnology, School of Agriculture, University of Ioannina, Arta, Greece
| | - Nikitas Prassinos
- School of Veterinary Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Nikolaos Diakakis
- School of Veterinary Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Dimitrios I. Zeugolis
- Regenerative, Modular & Developmental Engineering Laboratory (REMODEL), Charles Institute of Dermatology, Conway Institute of Biomolecular & Biomedical Research and School of Mechanical & Materials Engineering, University College Dublin (UCD), Dublin, Ireland
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Lyon MD, Ferreira JJ, Li P, Bhagwat S, Butler A, Anderson K, Polo M, Santi CM. SLO3: A Conserved Regulator of Sperm Membrane Potential. Int J Mol Sci 2023; 24:11205. [PMID: 37446382 DOI: 10.3390/ijms241311205] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 07/03/2023] [Accepted: 07/05/2023] [Indexed: 07/15/2023] Open
Abstract
Sperm cells must undergo a complex maturation process after ejaculation to be able to fertilize an egg. One component of this maturation is hyperpolarization of the membrane potential to a more negative value. The ion channel responsible for this hyperpolarization, SLO3, was first cloned in 1998, and since then much progress has been made to determine how the channel is regulated and how its function intertwines with various signaling pathways involved in sperm maturation. Although Slo3 was originally thought to be present only in the sperm of mammals, recent evidence suggests that a primordial form of the gene is more widely expressed in some fish species. Slo3, like many reproductive genes, is rapidly evolving with low conservation between closely related species and different regulatory and pharmacological profiles. Despite these differences, SLO3 appears to have a conserved role in regulating sperm membrane potential and driving large changes in response to stimuli. The effect of this hyperpolarization of the membrane potential may vary among mammalian species just as the regulation of the channel does. Recent discoveries have elucidated the role of SLO3 in these processes in human sperm and provided tools to target the channel to affect human fertility.
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Affiliation(s)
- Maximilian D Lyon
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Juan J Ferreira
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Ping Li
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Shweta Bhagwat
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Alice Butler
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Kelsey Anderson
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Maria Polo
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Celia M Santi
- Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, St. Louis, MO 63110, USA
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Xu J, Lv YT, Zhao XY, Wang JJ, Shen ZS, Li J, Zhang FF, Liu J, Wang XH, Xu Y, Geng Q, Ding YT, Xu JJ, Tan MJ, Li ZX, Wang R, Chen J, Sun W, Cui M, Logothetis DE, Cao JL, Tang QY, Zhang Z. Identification of Sodium- and Chloride-Sensitive Sites in the Slack Channel. J Neurosci 2023; 43:2665-2681. [PMID: 36898835 PMCID: PMC10089238 DOI: 10.1523/jneurosci.1365-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 02/24/2023] [Accepted: 02/28/2023] [Indexed: 03/12/2023] Open
Abstract
The Slack channel (KCNT1, Slo2.2) is a sodium-activated and chloride-activated potassium channel that regulates heart rate and maintains the normal excitability of the nervous system. Despite intense interest in the sodium gating mechanism, a comprehensive investigation to identify the sodium-sensitive and chloride-sensitive sites has been missing. In the present study, we identified two potential sodium-binding sites in the C-terminal domain of the rat Slack channel by conducting electrophysical recordings and systematic mutagenesis of cytosolic acidic residues in the rat Slack channel C terminus. In particular, by taking advantage of the M335A mutant, which results in the opening of the Slack channel in the absence of cytosolic sodium, we found that among the 92 screened negatively charged amino acids, E373 mutants could completely remove sodium sensitivity of the Slack channel. In contrast, several other mutants showed dramatic decreases in sodium sensitivity but did not abolish it altogether. Furthermore, molecular dynamics (MD) simulations performed at the hundreds of nanoseconds timescale revealed one or two sodium ions at the E373 position or an acidic pocket composed of several negatively charged residues. Moreover, the MD simulations predicted possible chloride interaction sites. By screening predicted positively charged residues, we identified R379 as a chloride interaction site. Thus, we conclude that the E373 site and the D863/E865 pocket are two potential sodium-sensitive sites, while R379 is a chloride interaction site in the Slack channel.SIGNIFICANCE STATEMENT The research presented here identified two distinct sodium and one chloride interaction sites located in the intracellular C-terminal domain of the Slack (Slo2.2, KCNT1) channel. Identification of the sites responsible for the sodium and chloride activation of the Slack channel sets its gating property apart from other potassium channels in the BK channel family. This finding sets the stage for future functional and pharmacological studies of this channel.
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Affiliation(s)
- Jie Xu
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Yan-Tian Lv
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Xiao-Yun Zhao
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Jing-Jing Wang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Zhong-Shan Shen
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Jian Li
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Fei-Fei Zhang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Jing Liu
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Xiao-Hui Wang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Yun Xu
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Qi Geng
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Yi-Tong Ding
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Jing-Jing Xu
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Meng-Jiao Tan
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Zhi-Xiao Li
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Ran Wang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Jian Chen
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Wen Sun
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Meng Cui
- Department of Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts 02115
| | - Diomedes E Logothetis
- Department of Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts 02115
| | - Jun-Li Cao
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Qiong-Yao Tang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
| | - Zhe Zhang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
- NMPA Key Laboratory for Research and Evaluation of Narcotic and Psychotropic Drugs, Xuzhou Medical University, Xuzhou 221004, People's Republic of China
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4
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Liang L, Liu H, Bartholdi D, van Haeringen A, Fernandez‐Jaén A, Peeters EEA, Xiong H, Bai X, Xu C, Ke T, Wang QK. Identification and functional analysis of two new de novo KCNMA1 variants associated with Liang-Wang syndrome. Acta Physiol (Oxf) 2022; 235:e13800. [PMID: 35156297 DOI: 10.1111/apha.13800] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2022] [Revised: 02/08/2022] [Accepted: 02/11/2022] [Indexed: 02/04/2023]
Abstract
AIM Loss-of-function KCNMA1 variants cause Liang-Wang syndrome (MIM #618729), a newly identified multiple malformation syndrome with a broad spectrum of developmental and neurological phenotypes. However, the full spectrum of clinical features and underlying pathogenic mechanisms need full elucidation. METHODS Exome sequencing was used to identify pathogenic variants. Patch-clamp recordings were performed to access the effects of KCNMA1 variants on BK channels. Total and membrane protein expression levels of BK channels were characterized using Western blotting. RESULTS We report identification and functional characterization of two new de novo loss-of-function KCNMA1 variants p.(A172T) and p.(A314T) with characteristics of Liang-Wang syndrome. Variant p.(A172T) is associated with developmental delay, cognitive impairment and ataxia. Mechanistically, p.(A172T) abolishes BK potassium current, inhibits Mg2+ -dependent gating, but shifts conductance-voltage (G-V) curves to more positive potentials when complexed with WT channels. Variant p.(A314T) is associated with developmental delay, intellectual disability, cognitive impairment, mild ataxia and generalized epilepsy; suppresses BK current amplitude; and shifts G-V curves to more positive potentials when expressed with WT channels. In addition, two new patients with previously reported gain-of-function variants p.(N536H) and p.(N995S) are found to show epilepsy and paroxysmal dyskinesia as reported previously, but also exhibit additional symptoms of cognitive impairment and dysmorphic features. Furthermore, variants p.(A314T) and p.(N536H) reduced total and membrane levels of BK proteins. CONCLUSION Our findings identified two new loss-of-function mutations of KCNMA1 associated with Liang-Wang syndrome, expanded the spectrum of clinical features associated with gain-of-function KCNMA1 variants and emphasized the overlapping features shared by gain-of-function and loss-of-function mutations.
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Affiliation(s)
- Lina Liang
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Huihui Liu
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Deborah Bartholdi
- Department of Human Genetics, Inselspital University Hospital Bern Bern Switzerland
| | - Arie van Haeringen
- Department of Clinical Genetics Leiden University Medical Center Leiden the Netherlands
| | - Alberto Fernandez‐Jaén
- Hospital Universitario Quirónsalud School of Medicine Universidad Europea de Madrid Madrid Spain
| | - Els E. A. Peeters
- Department of Child Neurology Juliana Children’s Hospital HAGA Medical Center The Hague the Netherlands
| | - Hongbo Xiong
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Xuemei Bai
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Chengqi Xu
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Tie Ke
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
| | - Qing K. Wang
- Center for Human Genome Research Key Laboratory of Molecular Biophysics of the Ministry of Education College of Life Science and Technology Huazhong University of Science and Technology Wuhan P. R. China
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5
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Kshatri AS, Gonzalez-Hernandez A, Giraldez T. Physiological Roles and Therapeutic Potential of Ca 2+ Activated Potassium Channels in the Nervous System. Front Mol Neurosci 2018; 11:258. [PMID: 30104956 PMCID: PMC6077210 DOI: 10.3389/fnmol.2018.00258] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 07/06/2018] [Indexed: 12/21/2022] Open
Abstract
Within the potassium ion channel family, calcium activated potassium (KCa) channels are unique in their ability to couple intracellular Ca2+ signals to membrane potential variations. KCa channels are diversely distributed throughout the central nervous system and play fundamental roles ranging from regulating neuronal excitability to controlling neurotransmitter release. The physiological versatility of KCa channels is enhanced by alternative splicing and co-assembly with auxiliary subunits, leading to fundamental differences in distribution, subunit composition and pharmacological profiles. Thus, understanding specific KCa channels’ mechanisms in neuronal function is challenging. Based on their single channel conductance, KCa channels are divided into three subtypes: small (SK, 4–14 pS), intermediate (IK, 32–39 pS) and big potassium (BK, 200–300 pS) channels. This review describes the biophysical characteristics of these KCa channels, as well as their physiological roles and pathological implications. In addition, we also discuss the current pharmacological strategies and challenges to target KCa channels for the treatment of various neurological and psychiatric disorders.
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Affiliation(s)
- Aravind S Kshatri
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Alberto Gonzalez-Hernandez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Teresa Giraldez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
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6
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Zhou Y, Yang H, Cui J, Lingle CJ. Threading the biophysics of mammalian Slo1 channels onto structures of an invertebrate Slo1 channel. J Gen Physiol 2017; 149:985-1007. [PMID: 29025867 PMCID: PMC5677106 DOI: 10.1085/jgp.201711845] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/20/2017] [Indexed: 11/24/2022] Open
Abstract
Zhou et al. consider the biophysics of large-conductance Ca2+-activated Slo1 channels in the context of Aplysia Slo1 structures. For those interested in the machinery of ion channel gating, the Ca2+ and voltage-activated BK K+ channel provides a compelling topic for investigation, by virtue of its dual allosteric regulation by both voltage and intracellular Ca2+ and because its large-single channel conductance facilitates detailed kinetic analysis. Over the years, biophysical analyses have illuminated details of the allosteric regulation of BK channels and revealed insights into the mechanism of BK gating, e.g., inner cavity size and accessibility and voltage sensor-pore coupling. Now the publication of two structures of an Aplysia californica BK channel—one liganded and one metal free—promises to reinvigorate functional studies and interpretation of biophysical results. The new structures confirm some of the previous functional inferences but also suggest new perspectives regarding cooperativity between Ca2+-binding sites and the relationship between voltage- and Ca2+-dependent gating. Here we consider the extent to which the two structures explain previous functional data on pore-domain properties, voltage-sensor motions, and divalent cation binding and activation of the channel.
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Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
| | - Huanghe Yang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University, St. Louis, MO
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
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7
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Geng Y, Ferreira JJ, Dzikunu V, Butler A, Lybaert P, Yuan P, Magleby KL, Salkoff L, Santi CM. A genetic variant of the sperm-specific SLO3 K + channel has altered pH and Ca 2+ sensitivities. J Biol Chem 2017; 292:8978-8987. [PMID: 28377504 DOI: 10.1074/jbc.m117.776013] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 03/21/2017] [Indexed: 11/06/2022] Open
Abstract
To fertilize an oocyte, sperm must first undergo capacitation in which the sperm plasma membrane becomes hyperpolarized via activation of potassium (K+) channels and resultant K+ efflux. Sperm-specific SLO3 K+ channels are responsible for these membrane potential changes critical for fertilization in mouse sperm, and they are only sensitive to pH i However, in human sperm, the major K+ conductance is both Ca2+- and pH i -sensitive. It has been debated whether Ca2+-sensitive SLO1 channels substitute for human SLO3 (hSLO3) in human sperm or whether human SLO3 channels have acquired Ca2+ sensitivity. Here we show that hSLO3 is rapidly evolving and reveal a natural structural variant with enhanced apparent Ca2+ and pH sensitivities. This variant allele (C382R) alters an amino acid side chain at a principal interface between the intramembrane-gated pore and the cytoplasmic gating ring of the channel. Because the gating ring contains sensors to intracellular factors such as pH and Ca2+, the effectiveness of transduction between the gating ring and the pore domain appears to be enhanced. Our results suggest that sperm-specific genes can evolve rapidly and that natural genetic variation may have led to a SLO3 variant that differs from wild type in both pH and intracellular Ca2+ sensitivities. Whether this physiological variation confers differences in fertility among males remains to be established.
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Affiliation(s)
- Yanyan Geng
- the Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, Florida 33136
| | | | | | | | | | - Peng Yuan
- Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110 and
| | - Karl L Magleby
- the Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, Florida 33136
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8
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Giraldez T, Rothberg BS. Understanding the conformational motions of RCK gating rings. J Gen Physiol 2017; 149:431-441. [PMID: 28246116 PMCID: PMC5379921 DOI: 10.1085/jgp.201611726] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/17/2017] [Indexed: 12/16/2022] Open
Abstract
A timely review of the structural basis of Ca2+-activated K+ channel modulation by regulator of conduction of K+ (RCK) domains Regulator of conduction of K+ (RCK) domains are ubiquitous regulators of channel and transporter activity in prokaryotes and eukaryotes. In humans, RCK domains form an integral component of large-conductance calcium-activated K channels (BK channels), key modulators of nerve, muscle, and endocrine cell function. In this review, we explore how the study of RCK domains in bacterial and human channels has contributed to our understanding of the structural basis of channel function. This knowledge will be critical in identifying mechanisms that underlie BK channelopathies that lead to epilepsy and other diseases, as well as regions of the channel that might be successfully targeted to treat such diseases.
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Affiliation(s)
- Teresa Giraldez
- Department of Basic Medical Sciences, Institute of Biomedical Technologies and Centre for Biomedical Research of the Canary Islands, Universidad de La Laguna, La Laguna 38071, Spain
| | - Brad S Rothberg
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA 19140
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9
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Latorre R, Castillo K, Carrasquel-Ursulaez W, Sepulveda RV, Gonzalez-Nilo F, Gonzalez C, Alvarez O. Molecular Determinants of BK Channel Functional Diversity and Functioning. Physiol Rev 2017; 97:39-87. [DOI: 10.1152/physrev.00001.2016] [Citation(s) in RCA: 151] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Large-conductance Ca2+- and voltage-activated K+ (BK) channels play many physiological roles ranging from the maintenance of smooth muscle tone to hearing and neurosecretion. BK channels are tetramers in which the pore-forming α subunit is coded by a single gene ( Slowpoke, KCNMA1). In this review, we first highlight the physiological importance of this ubiquitous channel, emphasizing the role that BK channels play in different channelopathies. We next discuss the modular nature of BK channel-forming protein, in which the different modules (the voltage sensor and the Ca2+ binding sites) communicate with the pore gates allosterically. In this regard, we review in detail the allosteric models proposed to explain channel activation and how the models are related to channel structure. Considering their extremely large conductance and unique selectivity to K+, we also offer an account of how these two apparently paradoxical characteristics can be understood consistently in unison, and what we have learned about the conduction system and the activation gates using ions, blockers, and toxins. Attention is paid here to the molecular nature of the voltage sensor and the Ca2+ binding sites that are located in a gating ring of known crystal structure and constituted by four COOH termini. Despite the fact that BK channels are coded by a single gene, diversity is obtained by means of alternative splicing and modulatory β and γ subunits. We finish this review by describing how the association of the α subunit with β or with γ subunits can change the BK channel phenotype and pharmacology.
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Affiliation(s)
- Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Romina V. Sepulveda
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Fernando Gonzalez-Nilo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Carlos Gonzalez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Osvaldo Alvarez
- Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile; Universidad Andres Bello, Facultad de Ciencias Biologicas, Center for Bioinformatics and Integrative Biology, Avenida Republica 239, Santiago, Chile and Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
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10
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Interactions of divalent cations with calcium binding sites of BK channels reveal independent motions within the gating ring. Proc Natl Acad Sci U S A 2016; 113:14055-14060. [PMID: 27872281 DOI: 10.1073/pnas.1611415113] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Large-conductance voltage- and calcium-activated K+ (BK) channels are key physiological players in muscle, nerve, and endocrine function by integrating intracellular Ca2+ and membrane voltage signals. The open probability of BK channels is regulated by the intracellular concentration of divalent cations sensed by a large structure in the BK channel called the "gating ring," which is formed by four tandems of regulator of conductance for K+ (RCK1 and RCK2) domains. In contrast to Ca2+ that binds to both RCK domains, Mg2+, Cd2+, or Ba2+ interact preferentially with either one or the other. Interaction of cations with their binding sites causes molecular rearrangements of the gating ring, but how these motions occur remains elusive. We have assessed the separate contributions of each RCK domain to the cation-induced gating-ring structural rearrangements, using patch-clamp fluorometry. Here we show that Mg2+ and Ba2+ selectively induce structural movement of the RCK2 domain, whereas Cd2+ causes motions of RCK1, in all cases substantially smaller than those elicited by Ca2+ By combining divalent species interacting with unique sites, we demonstrate that RCK1 and RCK2 domains move independently when their specific binding sites are occupied. Moreover, binding of chemically distinct cations to both RCK domains is additive, emulating the effect of fully occupied Ca2+ binding sites.
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11
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Modulation of BK Channel Function by Auxiliary Beta and Gamma Subunits. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2016; 128:51-90. [PMID: 27238261 DOI: 10.1016/bs.irn.2016.03.015] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The large-conductance, Ca(2+)- and voltage-activated K(+) (BK) channel is ubiquitously expressed in mammalian tissues and displays diverse biophysical or pharmacological characteristics. This diversity is in part conferred by channel modulation with different regulatory auxiliary subunits. To date, two distinct classes of BK channel auxiliary subunits have been identified: β subunits and γ subunits. Modulation of BK channels by the four auxiliary β (β1-β4) subunits has been well established and intensively investigated over the past two decades. The auxiliary γ subunits, however, were identified only very recently, which adds a new dimension to BK channel regulation and improves our understanding of the physiological functions of BK channels in various tissues and cell types. This chapter will review the current understanding of BK channel modulation by auxiliary β and γ subunits, especially the latest findings.
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12
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Yilmaz E, Kulke D, von Samson-Himmelstjerna G, Krücken J. Identification of novel splice variants of the voltage- and Ca²⁺-dependent K⁺-channel SLO-1 of Trichuris muris. Mol Biochem Parasitol 2015; 199:5-8. [PMID: 25779980 DOI: 10.1016/j.molbiopara.2015.03.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Revised: 03/04/2015] [Accepted: 03/05/2015] [Indexed: 02/04/2023]
Abstract
The anthelmintic cyclooctadepsipeptide emodepside is effective against nematodes showing resistance against established drug classes. Emodepside exerts its nematicidal effects mainly through its validated target, the tetrameric voltage- and calcium-activated potassium channel SLO-1. Two slo-1 genes were described in Trichuris muris. Alternative splicing is known to alter SLO-1 properties. Here, 16 T. muris splice variants for slo-1.1 and three variants for slo-1.2 were identified in addition to previously described variants. Splice variants caused by intron retentions and/or exon exclusions encode varyingly truncated subunits. Depending on the subunit composition, channels might have altered physiological and pharmacological properties including different modulation by calcium and/or voltage or reduced emodepside susceptibility which might lead to emodepside resistance as observed in Caenorhabditis elegans expressing only similarly truncated Slo-1. The comprehensive characterisation of splice variants is a prerequisite for functional analysis and confirmed conservation of remarkable differences found between both slo-1 paralogs in Trichuris suis.
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Affiliation(s)
- Esra Yilmaz
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany
| | - Daniel Kulke
- Global Drug Discovery - Animal Health - Parasiticides, Bayer HealthCare, 51368 Leverkusen, Germany
| | - Georg von Samson-Himmelstjerna
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany
| | - Jürgen Krücken
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany.
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13
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Kulke D, von Samson-Himmelstjerna G, Miltsch SM, Wolstenholme AJ, Jex AR, Gasser RB, Ballesteros C, Geary TG, Keiser J, Townson S, Harder A, Krücken J. Characterization of the Ca2+-gated and voltage-dependent K+-channel Slo-1 of nematodes and its interaction with emodepside. PLoS Negl Trop Dis 2014; 8:e3401. [PMID: 25521608 PMCID: PMC4270693 DOI: 10.1371/journal.pntd.0003401] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 11/07/2014] [Indexed: 11/18/2022] Open
Abstract
The cyclooctadepsipeptide emodepside and its parent compound PF1022A are broad-spectrum nematicidal drugs which are able to eliminate nematodes resistant to other anthelmintics. The mode of action of cyclooctadepsipeptides is only partially understood, but involves the latrophilin Lat-1 receptor and the voltage- and calcium-activated potassium channel Slo-1. Genetic evidence suggests that emodepside exerts its anthelmintic activity predominantly through Slo-1. Indeed, slo-1 deficient Caenorhabditis elegans strains are completely emodepside resistant. However, direct effects of emodepside on Slo-1 have not been reported and these channels have only been characterized for C. elegans and related Strongylida. Molecular and bioinformatic analyses identified full-length Slo-1 cDNAs of Ascaris suum, Parascaris equorum, Toxocara canis, Dirofilaria immitis, Brugia malayi, Onchocerca gutturosa and Strongyloides ratti. Two paralogs were identified in the trichocephalids Trichuris muris, Trichuris suis and Trichinella spiralis. Several splice variants encoding truncated channels were identified in Trichuris spp. Slo-1 channels of trichocephalids form a monophyletic group, showing that duplication occurred after the divergence of Enoplea and Chromadorea. To explore the function of a representative protein, C. elegans Slo-1a was expressed in Xenopus laevis oocytes and studied in electrophysiological (voltage-clamp) experiments. Incubation of oocytes with 1-10 µM emodepside caused significantly increased currents over a wide range of step potentials in the absence of experimentally increased intracellular Ca2+, suggesting that emodepside directly opens C. elegans Slo-1a. Emodepside wash-out did not reverse the effect and the Slo-1 inhibitor verruculogen was only effective when applied before, but not after, emodepside. The identification of several splice variants and paralogs in some parasitic nematodes suggests that there are substantial differences in channel properties among species. Most importantly, this study showed for the first time that emodepside directly opens a Slo-1 channel, significantly improving the understanding of the mode of action of this drug class.
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Affiliation(s)
- Daniel Kulke
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
- Global Drug Discovery, Animal Health, Parasiticides, Bayer HealthCare, Leverkusen, Germany
| | | | - Sandra M. Miltsch
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
| | - Adrian J. Wolstenholme
- Department of Infectious Diseases, College of Veterinary Medicine, The University of Georgia, Athens, Georgia, United States of America
| | - Aaron R. Jex
- Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Robin B. Gasser
- Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Cristina Ballesteros
- Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Timothy G. Geary
- Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Jennifer Keiser
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
| | - Simon Townson
- Tropical Parasitic Diseases Unit, Northwick Park Institute for Medical Research, Harrow, Middlesex, United Kingdom
| | - Achim Harder
- WE Biology, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
| | - Jürgen Krücken
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
- * E-mail:
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14
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Abstract
Ion channels are membrane-bound enzymes whose catalytic sites are ion-conducting pores that open and close (gate) in response to specific environmental stimuli. Ion channels are important contributors to cell signaling and homeostasis. Our current understanding of gating is the product of 60 plus years of voltage-clamp recording augmented by intervention in the form of environmental, chemical, and mutational perturbations. The need for good phenomenological models of gating has evolved in parallel with the sophistication of experimental technique. The goal of modeling is to develop realistic schemes that not only describe data, but also accurately reflect mechanisms of action. This review covers three areas that have contributed to the understanding of ion channels: traditional Eyring kinetic theory, molecular dynamics analysis, and statistical thermodynamics. Although the primary emphasis is on voltage-dependent channels, the methods discussed here are easily generalized to other stimuli and could be applied to any ion channel and indeed any macromolecule.
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15
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Mannowetz N, Naidoo NM, Choo SAS, Smith JF, Lishko PV. Slo1 is the principal potassium channel of human spermatozoa. eLife 2013; 2:e01009. [PMID: 24137539 PMCID: PMC3789364 DOI: 10.7554/elife.01009] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 09/02/2013] [Indexed: 12/21/2022] Open
Abstract
Mammalian spermatozoa gain competence to fertilize an oocyte as they travel through the female reproductive tract. This process is accompanied by an elevation of sperm intracellular calcium and a membrane hyperpolarization. The latter is evoked by K(+) efflux; however, the molecular identity of the potassium channel of human spermatozoa (hKSper) is unknown. Here, we characterize hKSper, reporting that it is regulated by intracellular calcium but is insensitive to intracellular alkalinization. We also show that human KSper is inhibited by charybdotoxin, iberiotoxin, and paxilline, while mouse KSper is insensitive to these compounds. Such unique properties suggest that the Slo1 ion channel is the molecular determinant for hKSper. We show that Slo1 is localized to the sperm flagellum and is inhibited by progesterone. Inhibition of hKSper by progesterone may depolarize the spermatozoon to open the calcium channel CatSper, thus raising [Ca(2+)] to produce hyperactivation and allowing sperm to fertilize an oocyte. DOI:http://dx.doi.org/10.7554/eLife.01009.001.
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Affiliation(s)
- Nadja Mannowetz
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Natasha M Naidoo
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Seung-A Sara Choo
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - James F Smith
- Department of Urology, University of California, San Francisco, San Francisco, United States
| | - Polina V Lishko
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
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16
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Molecular mechanisms of large-conductance ca (2+) -activated potassium channel activation by ginseng gintonin. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2013; 2013:323709. [PMID: 23662129 PMCID: PMC3638619 DOI: 10.1155/2013/323709] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/05/2013] [Accepted: 03/12/2013] [Indexed: 01/12/2023]
Abstract
Gintonin is a unique lysophosphatidic acid (LPA) receptor ligand
found in Panax ginseng. Gintonin induces transient
[Ca2+]i
through G protein-coupled LPA receptors. Large-conductance Ca2+-activated
K+ (BKCa)
channels are expressed in blood vessels and neurons and
play important roles in blood vessel relaxation and attenuation of
neuronal excitability. BKCa channels are activated by transient
[Ca2+]i
and are regulated by various Ca2+-dependent kinases. We
investigated the molecular mechanisms of BKCa channel activation
by gintonin. BKCa channels are heterologously expressed in
Xenopus oocytes. Gintonin treatment induced BKCa channel activation in
oocytes expressing the BKCa channel α subunit in a
concentration-dependent manner (EC50 = 0.71 ± 0.08 µg/mL).
Gintonin-mediated BKCa channel activation was blocked by a PKC
inhibitor, calphostin, and by the calmodulin inhibitor,
calmidazolium. Site-directed mutations in BKCa channels targeting
CaM kinase II or PKC phosphorylation sites but not PKA
phosphorylation sites attenuated gintonin action. Mutations in the
Ca2+ bowl and the regulator of K+ conductance (RCK) site also
blocked gintonin action. These results indicate that
gintonin-mediated BKCa channel activations are achieved through
LPA1 receptor-phospholipase C-IP3-Ca2+-PKC-calmodulin-CaM kinase
II pathways and calcium binding to the Ca2+ bowl and RCK domain.
Gintonin could be a novel contributor against blood vessel
constriction and over-excitation of neurons.
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17
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State-dependent FRET reports calcium- and voltage-dependent gating-ring motions in BK channels. Proc Natl Acad Sci U S A 2013; 110:5217-22. [PMID: 23479636 DOI: 10.1073/pnas.1219611110] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Large-conductance voltage- and calcium-dependent potassium channels (BK, "Big K+") are important controllers of cell excitability. In the BK channel, a large C-terminal intracellular region containing a "gating-ring" structure has been proposed to transduce Ca(2+) binding into channel opening. Using patch-clamp fluorometry, we have investigated the calcium and voltage dependence of conformational changes of the gating-ring region of BK channels, while simultaneously monitoring channel conductance. Fluorescence resonance energy transfer (FRET) between fluorescent protein inserts indicates that Ca(2+) binding produces structural changes of the gating ring that are much larger than those predicted by current X-ray crystal structures of isolated gating rings.
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18
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Levitsky DO, Takahashi M. Interplay of Ca(2+) and Mg (2+) in sodium-calcium exchanger and in other Ca(2+)-binding proteins: magnesium, watchdog that blocks each turn if able. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:65-78. [PMID: 23224871 DOI: 10.1007/978-1-4614-4756-6_7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Sodium-calcium exchange across plasma membrane is regulated by intracellular calcium ions. The sodium-calcium exchanger (NCX1) is activated by successive saturation of numerous Ca(2+)-binding sites located in the intracellular loop of the protein. The progressive saturation of the binding domain CBD12 by Ca(2+) results in a series of conformational changes of CBD12 as well as of entire NCX1 molecule. Like other soluble and membrane Ca(2+)-binding proteins, NCX1 can also be regulated by Mg(2+) that antagonises Ca(2+) at the level of divalent cation-binding sites. This chapter summarises data on Mg(2+) impacts in the cells. Regulatory action of Mg(2+) on intracellular Ca(2+)-dependent processes can be achieved due to changes of its cytoplasmic level, which take place in the range of [Mg(2+)](i) from 0.5 to 3 mM. Under normal conditions, these changes are ensured by activation of plasmalemmal Mg(2+) transport systems and by variations in ATP level in cytoplasm. In heart and in brain, some pathological conditions, such as hypoxia, ischemia and ischemia followed by reperfusion, are associated with an important increase in intracellular Ca(2+). The tissue damage due to Ca(2+) overload may be prevented by Mg(2+). The protective actions of Mg(2+) can be achieved due to its ability to compete with Ca(2+) for the binding sites in a number of proteins responsible for the rise in intracellular free Ca(2+), including NCX1, in case when the reverse mode of Na(+)/Ca(2+) exchange becomes predominant. Saturation of CBD12 by Mg(2+) results in important changes of NCX1 conformation. Modulating actions of Mg(2+) on the conformation of NCX1 were detected at a narrow range of Mg(2+) concentration, from 0.5 to 1 mM. These data support an idea that variations of intracellular Mg(2+) could modify transmembrane Ca(2+) movements ensured by NCX1.
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Affiliation(s)
- Dmitri O Levitsky
- Unité de Fonctionnalité et Ingénierie des Protéines, Université de Nantes, Nantes Cedex 03, France.
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19
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Rothberg BS. The BK channel: a vital link between cellular calcium and electrical signaling. Protein Cell 2012; 3:883-92. [PMID: 22996175 PMCID: PMC4875380 DOI: 10.1007/s13238-012-2076-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Accepted: 08/23/2012] [Indexed: 10/27/2022] Open
Abstract
Large-conductance Ca²⁺-activated K⁺ channels (BK channels) constitute an key physiological link between cellular Ca²⁺ signaling and electrical signaling at the plasma membrane. Thus these channels are critical to the control of action potential firing and neurotransmitter release in several types of neurons, as well as the dynamic control of smooth muscle tone in resistance arteries, airway, and bladder. Recent advances in our understanding of K⁺ channel structure and function have led to new insight toward the molecular mechanisms of opening and closing (gating) of these channels. Here we will focus on mechanisms of BK channel gating by Ca²⁺, transmembrane voltage, and auxiliary subunit proteins.
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Affiliation(s)
- Brad S Rothberg
- Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140, USA.
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20
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Félétou M. The Endothelium, Part I: Multiple Functions of the Endothelial Cells -- Focus on Endothelium-Derived Vasoactive Mediators. ACTA ACUST UNITED AC 2011. [DOI: 10.4199/c00031ed1v01y201105isp019] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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21
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22
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Telezhkin V, Brazier SP, Mears R, Müller CT, Riccardi D, Kemp PJ. Cysteine residue 911 in C-terminal tail of human BKCaα channel subunit is crucial for its activation by carbon monoxide. Pflugers Arch 2011; 461:665-75. [DOI: 10.1007/s00424-011-0924-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 01/10/2011] [Accepted: 01/12/2011] [Indexed: 12/20/2022]
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23
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Choi SH, Shin TJ, Lee BH, Hwang SH, Lee SM, Lee BC, Park CS, Ha TS, Nah SY. Ginsenoside Rg3 enhances large conductance Ca2+-activated potassium channel currents: a role of Tyr360 residue. Mol Cells 2011; 31:133-40. [PMID: 21191818 PMCID: PMC3932677 DOI: 10.1007/s10059-011-0017-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 10/25/2010] [Accepted: 11/13/2010] [Indexed: 10/18/2022] Open
Abstract
Ginsenosides, active ingredients of Panax ginseng, are known to exhibit neuroprotective effects. Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels are key modulators of cellular excitability of neurons and vascular smooth muscle cells. In the present study, we examined the effects of ginsenosides on rat brain BK(Ca) (rSlo) channel activity heterologously expressed in Xenopus oocytes to elucidate the molecular mechanisms how ginsenoside regulates the BK(Ca) channel activity. Ginsenoside Rg(3) (Rg(3)) enhanced outward BK(Ca) channel currents. The Rg(3)-enhancement of outward BK(Ca) channel currents was concentration-dependent, voltage-dependent, and reversible. The EC(50) was 15.1 ± 3.1 μM. Rg(3) actions were not desensitized by repeated treatment. Tetraetylammonium (TEA), a K(+) channel blocker, inhibited BK(Ca) channel currents. We examined whether extracellular TEA treatment could alter the Rg(3) action and vice versa. TEA caused a rightward shift of the Rg(3) concentration-response curve (i.e., much higher concentration of Rg(3) is required for the activation of BK(Ca) channel compared to the absence of TEA), while Rg(3) caused a rightward shift of the TEA concentration-response curve in wild-type channels. Mutation of the extracellular TEA binding site Y360 to Y360I caused a rightward shift of the TEA concentration-response curve and almost abolished both the Rg(3) action and Rg(3)-induced rightward shift of TEA concentration-response curve. These results indicate that Tyr360 residue of BK(Ca) channel plays an important role in the Rg(3)-enhancement of BK(Ca) channel currents.
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Affiliation(s)
- Sun-Hye Choi
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Tae-Joon Shin
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Byung-Hwan Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Sung Hee Hwang
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Sang-Mok Lee
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
| | - Byung-Cheol Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Cheol-Seung Park
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Tal Soo Ha
- Department of Molecular Biology, College of Natural Science, Daegu University, Gyeongsan 712-714, Korea
| | - Seung-Yeol Nah
- Ginsentology Research Laboratory and Department of Physiology, College of Veterinary Medicine and Bio/Molecular Informatics Center, Konkuk University, Seoul 143-701, Korea
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24
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Abstract
BK potassium channels regulate spike width and firing rate. A BK point mutation in humans enhances channel activity, leading to epilepsy. In this issue of Neuron, Yang and colleagues use this mutation to demonstrate that channel opening is determined by the flexibility of a region that contains a Ca(2+)-binding site.
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Yang J, Krishnamoorthy G, Saxena A, Zhang G, Shi J, Yang H, Delaloye K, Sept D, Cui J. An epilepsy/dyskinesia-associated mutation enhances BK channel activation by potentiating Ca2+ sensing. Neuron 2010; 66:871-83. [PMID: 20620873 DOI: 10.1016/j.neuron.2010.05.009] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/03/2010] [Indexed: 10/19/2022]
Abstract
Ca(2+)-activated BK channels modulate neuronal activities, including spike frequency adaptation and synaptic transmission. Previous studies found that Ca(2+)-binding sites and the activation gate are spatially separated in the channel protein, but the mechanism by which Ca(2+) binding opens the gate over this distance remains unknown. By studying an Asp-to-Gly mutation (D434G) associated with human syndrome of generalized epilepsy and paroxysmal dyskinesia (GEPD), we show that a cytosolic motif immediately following the activation gate S6 helix, known as the AC region, mediates the allosteric coupling between Ca(2+) binding and channel opening. The GEPD mutation inside the AC region increases BK channel activity by enhancing this allosteric coupling. We found that Ca(2+) sensitivity is enhanced by increases in solution viscosity that reduce protein dynamics. The GEPD mutation alters such a response, suggesting that a less flexible AC region may be more effective in coupling Ca(2+) binding to channel opening.
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Affiliation(s)
- Junqiu Yang
- Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, MO 63130, USA
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26
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Cui J. BK-type calcium-activated potassium channels: coupling of metal ions and voltage sensing. J Physiol 2010; 588:4651-8. [PMID: 20660558 DOI: 10.1113/jphysiol.2010.194514] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Ion channels and lipid phosphatases adopt a transmembrane voltage sensor domain (VSD) that moves in response to physiological variations of the membrane potential to control their activities. However, the VSD movements and coupling to the channel or phosphatase activities may differ depending on various interactions between the VSD and its host molecules. BK-type voltage, Ca²(+) and Mg²(+) activated K(+) channels contain the VSD and a large cytosolic domain (CTD) that binds Ca²(+)and Mg²(+). VSD movements are coupled to BK channel opening with a unique allosteric mechanism and are modulated by Ca²(+) and Mg²(+) binding via the interactions among the channel pore, VSD and CTD. These properties are energetically advantageous for the pore to be controlled by multiple stimuli, revealing the adaptability of the VSD to its host molecules and showing the potential for intracellular signals to affect the VSD in order to modulate the function of its host molecules.
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Affiliation(s)
- Jianmin Cui
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, MO 63130, USA.
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27
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Yusifov T, Javaherian AD, Pantazis A, Gandhi CS, Olcese R. The RCK1 domain of the human BKCa channel transduces Ca2+ binding into structural rearrangements. ACTA ACUST UNITED AC 2010; 136:189-202. [PMID: 20624858 PMCID: PMC2912072 DOI: 10.1085/jgp.200910374] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Large-conductance voltage- and Ca2+-activated K+ (BKCa) channels play a fundamental role in cellular function by integrating information from their voltage and Ca2+ sensors to control membrane potential and Ca2+ homeostasis. The molecular mechanism of Ca2+-dependent regulation of BKCa channels is unknown, but likely relies on the operation of two cytosolic domains, regulator of K+ conductance (RCK)1 and RCK2. Using solution-based investigations, we demonstrate that the purified BKCa RCK1 domain adopts an α/β fold, binds Ca2+, and assembles into an octameric superstructure similar to prokaryotic RCK domains. Results from steady-state and time-resolved spectroscopy reveal Ca2+-induced conformational changes in physiologically relevant [Ca2+]. The neutralization of residues known to be involved in high-affinity Ca2+ sensing (D362 and D367) prevented Ca2+-induced structural transitions in RCK1 but did not abolish Ca2+ binding. We provide evidence that the RCK1 domain is a high-affinity Ca2+ sensor that transduces Ca2+ binding into structural rearrangements, likely representing elementary steps in the Ca2+-dependent activation of human BKCa channels.
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Affiliation(s)
- Taleh Yusifov
- Division of Molecular Medicine, Department of Anesthesiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095, USA
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28
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Telezhkin V, Brazier SP, Cayzac SH, Wilkinson WJ, Riccardi D, Kemp PJ. Mechanism of inhibition by hydrogen sulfide of native and recombinant BKCa channels. Respir Physiol Neurobiol 2010; 172:169-78. [PMID: 20576528 DOI: 10.1016/j.resp.2010.05.016] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Revised: 05/06/2010] [Accepted: 05/11/2010] [Indexed: 12/17/2022]
Abstract
Recent evidence suggests that H(2)S contributes to activation of the carotid body by hypoxia by inhibiting K(+) channels. Here, we determine both the molecular identity of the K(+) channel target within the carotid body and the biophysical characteristics of the H(2)S-evoked inhibition by analyzing native rat and human recombinant BK(Ca) channel activity in voltage-clamped, inside-out membrane patches. Rat glomus cells express the enzymes necessary for the endogenous generation of H(2)S, cystathionine-beta-synthase and cystathionine-gamma-lyase. H(2)S inhibits native carotid body and human recombinant BK(Ca) channels with IC(50) values of around 275 microM. Inhibition by H(2)S is rapid and reversible, works by a mechanism which is distinct from that suggested for CO gas regulation of this channel and does not involve an interaction with either the "Ca bowl" or residues distal to this Ca(2+)-sensing domain. These data show that BK(Ca) is a K(+) channel target of H(2)S, and suggest a mechanism to explain the H(2)S-dependent component of O(2) sensing in the carotid body.
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Affiliation(s)
- Vsevolod Telezhkin
- Division of Pathophysiology and Repair, School of Biosciences, Cardiff University, Cardiff, UK
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29
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Abstract
Although a unifying characteristic common to all transient receptor potential (TRP) channel functions remains elusive, they could be described as tetramers formed by subunits with six transmembrane domains and containing cation-selective pores, which in several cases show high calcium permeability. TRP channels constitute a large superfamily of ion channels, and can be grouped into seven subfamilies based on their amino acid sequence homology: the canonical or classic TRPs, the vanilloid receptor TRPs, the melastatin or long TRPs, ankyrin (whose only member is the transmembrane protein 1 [TRPA1]), TRPN after the nonmechanoreceptor potential C (nonpC), and the more distant cousins, the polycystins and mucolipins. Because of their role as cellular sensors, polymodal activation and gating properties, many TRP channels are activated by a variety of different stimuli and function as signal integrators. Thus, how TRP channels function and how function relates to given structural determinants contained in the channel-forming protein has attracted the attention of biophysicists as well as molecular and cell biologists. The main purpose of this review is to summarize our present knowledge on the structure of channels of the TRP ion channel family. In the absence of crystal structure information for a complete TRP channel, we will describe important protein domains present in TRP channels, structure-function mutagenesis studies, the few crystal structures available for some TRP channel modules, and the recent determination of some TRP channel structures using electron microscopy.
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30
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Lee JH, Kim HJ, Kim HD, Lee BC, Chun JS, Park CS. Modulation of the conductance-voltage relationship of the BK(Ca) channel by shortening the cytosolic loop connecting two RCK domains. Biophys J 2009; 97:730-7. [PMID: 19651031 DOI: 10.1016/j.bpj.2009.04.058] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 04/20/2009] [Accepted: 04/24/2009] [Indexed: 12/25/2022] Open
Abstract
Calcium-dependent gating of large-conductance calcium-activated potassium (BK(Ca)) channels is mediated by the intracellular carboxyl terminus, which contains two domains of regulator of K(+) conductance (RCK). In mammalian BK(Ca) channels, the two RCK domains are separated by a protein segment of 101 residues that is poorly conserved in evolution and predicted to have no regular secondary structures. We investigated the functional importance of this loop using a series of deletion mutations. We found that the length, rather than the specific sequence at the central region of the segment, is critical for the functionality of the channel. As the length of the loop is progressively shorted, the conductance-voltage relationship gradually shifts toward more positive voltages with a minimum length of 70 amino acids, in an apparent response to increased tension within the loop. Thus, the functional activity of the BK(Ca) channel can be modulated by altering the tension of this loop region.
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Affiliation(s)
- Ju-Ho Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju, Korea
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31
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Santi CM, Butler A, Kuhn J, Wei A, Salkoff L. Bovine and mouse SLO3 K+ channels: evolutionary divergence points to an RCK1 region of critical function. J Biol Chem 2009; 284:21589-98. [PMID: 19473978 DOI: 10.1074/jbc.m109.015040] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The slo3 gene encodes a K(+) channel found only in mammalian testis. This is in contrast to slo1, which is expressed in many tissues. Genes pertaining to male reproduction, especially those involved in sperm production, evolve morphologically and functionally much faster than their nonsexual counterparts. A comparison of SLO3 channel amino acid sequences from several species revealed a high degree of structural divergence relative to their SLO1 channel paralogues. To reveal any biophysical differences accompanying this rapid structural divergence, we analyzed the functional properties of SLO3 channels from two species, bovine and mouse. We observed several functional differences including voltage range of activation, kinetics, and pH sensitivity. Although SLO3 channel proteins from these two species lack conservation in many structural regions, we found that the first two of these three functional differences map to the same loop structure in their RCK1 (regulator of K(+) conductance 1) domain, which links the intermediate RCK1 subdomain to the C-terminal subdomain. We found that small structural changes in this region produce major changes in the voltage range of activation and kinetics. This rapidly evolving loop peptide shows the greatest length and sequence polymorphisms within RCK1 domains from many different species. In SLO3 channels this region may permit evolutionary changes that tune the gating properties in different species.
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Affiliation(s)
- Celia M Santi
- Department of Anatomy and Neurobiology, Genetics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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32
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Abstract
Large conductance, Ca(2+)-activated potassium (BK) channels are widely expressed throughout the animal kingdom and play important roles in many physiological processes, such as muscle contraction, neural transmission and hearing. These physiological roles derive from the ability of BK channels to be synergistically activated by membrane voltage, intracellular Ca(2+) and other ligands. Similar to voltage-gated K(+) channels, BK channels possess a pore-gate domain (S5-S6 transmembrane segments) and a voltage-sensor domain (S1-S4). In addition, BK channels contain a large cytoplasmic C-terminal domain that serves as the primary ligand sensor. The voltage sensor and the ligand sensor allosterically control K(+) flux through the pore-gate domain in response to various stimuli, thereby linking cellular metabolism and membrane excitability. This review summarizes the current understanding of these structural domains and their mutual interactions in voltage-, Ca(2+)- and Mg(2+)-dependent activation of the channel.
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Affiliation(s)
- J Cui
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, 1 Brookings Drive, St. Louis, Missouri 63130, USA.
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33
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Kubokawa M, Sohma Y, Hirano J, Nakamura K, Kubota T. Intracellular Mg2+ influences both open and closed times of a native Ca2+-activated BK channel in cultured human renal proximal tubule cells. J Membr Biol 2009; 207:69-89. [PMID: 16477529 DOI: 10.1007/s00232-005-0802-3] [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: 12/01/2004] [Revised: 10/20/2005] [Indexed: 12/22/2022]
Abstract
Effects of intracellular Mg2+ on a native Ca(2+)-and voltage-sensitive large-conductance K+ channel in cultured human renal proximal tubule cells were examined with the patch-clamp technique in the inside-out mode. At an intracellular concentration of Ca2+ ([Ca2+](i)) of 10(-5)-10(-4) M, addition of 1-10 mM: Mg2+ increased the open probability (P(o)) of the channel, which shifted the P(o) -membrane potential (V(m)) relationship to the negative voltage direction without causing an appreciable change in the gating charge (Boltzmann constant). However, the Mg(2+)-induced increase in P(o) was suppressed at a relatively low [Ca2+](i) (10(-5.5)-10(-6) M). Dwell-time histograms have revealed that addition of Mg2+ mainly increased P(o) by extending open times at 10(-5) M Ca2+ and extending both open and closed times simultaneously at 10(-5.5) M Ca2+. Since our data showed that raising the [Ca2+](i) from 10(-5) to 10(-4) M increased P(o) mainly by shortening the closed time, extension of the closed time at 10(-5.5) M Ca(2+) would result from the Mg(2+)-inhibited Ca(2+)-dependent activation. At a constant V(m), adding Mg2+ enhanced the sigmoidicity of the P(o)-[Ca2+](i) relationship with an increase in the Hill coefficient. These results suggest that the major action of Mg2+ on this channel is to elevate P(o) by lengthening the open time, while extension of the closed time at a relatively low [Ca2+](i) results from a lowering of the sensitivity to Ca2+ of the channel by Mg2+, which causes the increase in the Hill coefficient.
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Affiliation(s)
- M Kubokawa
- Department of Physiology II, School of Medicine, Iwate Medical University, 19-1, Uchimaru, Morioka, 020-8505, Japan.
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34
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Xiao Q, Prussia A, Yu K, Cui YY, Hartzell HC. Regulation of bestrophin Cl channels by calcium: role of the C terminus. ACTA ACUST UNITED AC 2009; 132:681-92. [PMID: 19029375 PMCID: PMC2585866 DOI: 10.1085/jgp.200810056] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Human bestrophin-1 (hBest1), which is genetically linked to several kinds of retinopathy and macular degeneration in both humans and dogs, is the founding member of a family of Cl− ion channels that are activated by intracellular Ca2+. At present, the structures and mechanisms responsible for Ca2+ sensing remain unknown. Here, we have used a combination of molecular modeling, density functional–binding energy calculations, mutagenesis, and patch clamp to identify the regions of hBest1 involved in Ca2+ sensing. We identified a cluster of a five contiguous acidic amino acids in the C terminus immediately after the last transmembrane domain, followed by an EF hand and another regulatory domain that are essential for Ca2+ sensing by hBest1. The cluster of five amino acids (293–308) is crucial for normal channel gating by Ca2+ because all but two of the 35 mutations we made in this region rendered the channel incapable of being activated by Ca2+. Using homology models built on the crystal structure of calmodulin (CaM), an EF hand (EF1) was identified in hBest1. EF1 was predicted to bind Ca2+ with a slightly higher affinity than the third EF hand of CaM and lower affinity than the second EF hand of troponin C. As predicted by the model, the D312G mutation in the putative Ca2+-binding loop (312–323) reduced the apparent Ca2+ affinity by 20-fold. In addition, the D312G and D323N mutations abolished Ca2+-dependent rundown of the current. Furthermore, analysis of truncation mutants of hBest1 identified a domain adjacent to EF1 that is rich in acidic amino acids (350–390) that is required for Ca2+ activation and plays a role in current rundown. These experiments identify a region of hBest1 (312–323) that is involved in the gating of hBest1 by Ca2+ and suggest a model in which Ca2+ binding to EF1 activates the channel in a process that requires the acidic domain (293–308) and another regulatory domain (350–390). Many of the ∼100 disease-causing mutations in hBest1 are located in this region that we have implicated in Ca2+ sensing, suggesting that these mutations disrupt hBest1 channel gating by Ca2+.
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Affiliation(s)
- Qinghuan Xiao
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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35
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Sweet TB, Cox DH. Measurements of the BKCa channel's high-affinity Ca2+ binding constants: effects of membrane voltage. ACTA ACUST UNITED AC 2009; 132:491-505. [PMID: 18955592 PMCID: PMC2571968 DOI: 10.1085/jgp.200810094] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
It has been established that the large conductance Ca2+-activated K+ channel contains two types of high-affinity Ca2+ binding sites, termed the Ca2+ bowl and the RCK1 site. The affinities of these sites, and how they change as the channel opens, is still a subject of some debate. Previous estimates of these affinities have relied on fitting a series of conductance–voltage relations determined over a series of Ca2+ concentrations with models of channel gating that include both voltage sensing and Ca2+ binding. This approach requires that some model of voltage sensing be chosen, and differences in the choice of voltage-sensing model may underlie the different estimates that have been produced. Here, to better determine these affinities we have measured Ca2+ dose–response curves of channel activity at constant voltage for the wild-type mSlo channel (minus its low-affinity Ca2+ binding site) and for channels that have had one or the other Ca2+ binding site disabled via mutation. To accurately determine these dose–response curves we have used a series of 22 Ca2+ concentrations, and we have used unitary current recordings, coupled with changes in channel expression level, to measure open probability over five orders of magnitude. Our results indicate that at −80 mV the Ca2+ bowl has higher affinity for Ca2+ than does the RCK1 site in both the opened and closed conformations of the channel, and that the binding of Ca2+ to the RCK1 site is voltage dependent, whereas at the Ca2+ bowl it is not.
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Affiliation(s)
- Tara-Beth Sweet
- Molecular Cardiology Research Institute, Tufts Medical Center, Tufts University School of Medicine, Boston, MA 02111, USA
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36
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Abstract
The set of genes that underlie ethanol tolerance (inducible resistance) are likely to overlap with the set of genes responsible for ethanol addiction. Whereas addiction is difficult to recognize in simple model systems, behavioral tolerance is readily identifiable and can be induced in large populations of animals. Thus, tolerance lends itself to analysis in model systems with powerful genetics. Drosophila melanogaster has been used by a variety of laboratories for the identification of genes that interfere with the acquisition of ethanol tolerance. Here, I discuss the genes identified as being important for the production of ethanol tolerance in Drosophila. Some of these genes have also been shown to be important for the production of tolerance in mammals, demonstrating that gene discovery in Drosophila has predictive value for understanding the molecular pathways that generate tolerance in mammals.
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Affiliation(s)
- Nigel S Atkinson
- Section of Neurobiology and The Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas 78712-0248, USA.
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37
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Impaired Ca2+-dependent activation of large-conductance Ca2+-activated K+ channels in the coronary artery smooth muscle cells of Zucker Diabetic Fatty rats. Biophys J 2008; 95:5165-77. [PMID: 18790848 DOI: 10.1529/biophysj.108.138339] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The large-conductance Ca(2+)-activated K(+) (BK) channels play an important role in the regulation of cellular excitability in response to changes in intracellular metabolic state and Ca(2+) homeostasis. In vascular smooth muscle, BK channels are key determinants of vasoreactivity and vital-organ perfusion. Vascular BK channel functions are impaired in diabetes mellitus, but the mechanisms underlying such changes have not been examined in detail. We examined and compared the activities and kinetics of BK channels in coronary arterial smooth muscle cells from Lean control and Zucker Diabetic Fatty (ZDF) rats, using single-channel recording techniques. We found that BK channels in ZDF rats have impaired Ca(2+) sensitivity, including an increased free Ca(2+) concentration at half-maximal effect on channel activation, a reduced steepness of Ca(2+) dose-dependent curve, altered Ca(2+)-dependent gating properties with decreased maximal open probability, and a shortened mean open-time and prolonged mean closed-time durations. In addition, the BK channel beta-subunit-mediated activation by dehydrosoyasaponin-1 (DHS-1) was lost in cells from ZDF rats. Immunoblotting analysis confirmed a 2.1-fold decrease in BK channel beta(1)-subunit expression in ZDF rats, compared with that of Lean rats. These abnormalities in BK channel gating lead to an increase in the energy barrier for channel activation, and may contribute to the development of vascular dysfunction and complications in type 2 diabetes mellitus.
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38
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Yusifov T, Savalli N, Gandhi CS, Ottolia M, Olcese R. The RCK2 domain of the human BKCa channel is a calcium sensor. Proc Natl Acad Sci U S A 2008; 105:376-81. [PMID: 18162557 PMCID: PMC2224220 DOI: 10.1073/pnas.0705261105] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Indexed: 12/21/2022] Open
Abstract
Large conductance voltage and Ca(2+)-dependent K(+) channels (BK(Ca)) are activated by both membrane depolarization and intracellular Ca(2+). Recent studies on bacterial channels have proposed that a Ca(2+)-induced conformational change within specialized regulators of K(+) conductance (RCK) domains is responsible for channel gating. Each pore-forming alpha subunit of the homotetrameric BK(Ca) channel is expected to contain two intracellular RCK domains. The first RCK domain in BK(Ca) channels (RCK1) has been shown to contain residues critical for Ca(2+) sensitivity, possibly participating in the formation of a Ca(2+)-binding site. The location and structure of the second RCK domain in the BK(Ca) channel (RCK2) is still being examined, and the presence of a high-affinity Ca(2+)-binding site within this region is not yet established. Here, we present a structure-based alignment of the C terminus of BK(Ca) and prokaryotic RCK domains that reveal the location of a second RCK domain in human BK(Ca) channels (hSloRCK2). hSloRCK2 includes a high-affinity Ca(2+)-binding site (Ca bowl) and contains similar secondary structural elements as the bacterial RCK domains. Using CD spectroscopy, we provide evidence that hSloRCK2 undergoes a Ca(2+)-induced change in conformation, associated with an alpha-to-beta structural transition. We also show that the Ca bowl is an essential element for the Ca(2+)-induced rearrangement of hSloRCK2. We speculate that the molecular rearrangements of RCK2 likely underlie the Ca(2+)-dependent gating mechanism of BK(Ca) channels. A structural model of the heterodimeric complex of hSloRCK1 and hSloRCK2 domains is discussed.
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Affiliation(s)
- Taleh Yusifov
- *Division of Molecular Medicine, Department of Anesthesiology
| | | | - Chris S. Gandhi
- Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, MC 114-96, California Institute of Technology, Pasadena, CA 91125
| | - Michela Ottolia
- Cardiovascular Research Laboratory, and
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-7115; and
| | - Riccardo Olcese
- *Division of Molecular Medicine, Department of Anesthesiology
- Brain Research Institute
- Cardiovascular Research Laboratory, and
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SLO, SLO, quick, quick, slow: calcium-activated potassium channels as regulators of Caenorhabditis elegans behaviour and targets for anthelmintics. INVERTEBRATE NEUROSCIENCE 2007; 7:199-208. [PMID: 17962986 DOI: 10.1007/s10158-007-0057-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Accepted: 10/09/2007] [Indexed: 12/26/2022]
Abstract
Large-conductance calcium and voltage-activated potassium channels, termed SLO-1 (or BK), are pivotal players in the regulation of cell excitability across the animal phyla. Furthermore, emerging evidence indicates that these channels are key mediators of a number of neuroactive drugs, including the most recent new anthelmintic, the cyclo-octadepsipeptide emodepside. Detailed reviews of the structure, function and pharmacology of BK channels have recently been provided (Salkoff et al. in Nat Rev Neurosci 7:921-931, 2006; Ghatta et al. in Pharmacol Ther 110:103-116, 2006) and therefore these aspects will only briefly be covered here. The purpose of this review is to discuss how SLO-1 channels might function as regulators of neural transmission and network activity. In particular, we focus on the role of SLO-1 in the regulation of Caenorhabditis elegans behaviour and highlight the role of this channel as an effector for pleiotropic actions of neuroactive drugs, including emodepside. On the premise that C. elegans is a 'model nematode' with respect to many aspects of neural function, the intention is that this might inform a broader understanding of the role of these channels in the nematodes and their potential as novel anthelmintic targets.
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40
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Kim HJ, Lim HH, Rho SH, Bao L, Lee JH, Cox DH, Kim DH, Park CS. Modulation of the conductance-voltage relationship of the BK Ca channel by mutations at the putative flexible interface between two RCK domains. Biophys J 2007; 94:446-56. [PMID: 17890381 PMCID: PMC2157237 DOI: 10.1529/biophysj.107.108738] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Calcium-dependent gating of the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel is conferred by the large cytosolic carboxyl terminus containing two domains of the regulator of K(+) conductance (RCK) and the high-affinity Ca(2+)-binding site (the Ca(2+)-bowl). In our previous study, we located the putative second RCK domain (RCK2) and demonstrated that it interacts directly with RCK1 via a hydrophobic "assembly interface". In this study, we tested the structural model of the other interface, the "flexible interface", by strategically positioning charge pairs across the putative interface. Several charge mutations on RCK2 affected the voltage-dependent activation of the channel. In particular, the Gly-to-Asp substitution at position 803 profoundly affected channel activation by stabilizing the open conformation of the channel with minimal effects on its Ca(2+) affinity and voltage sensitivity. Various mutations at Gly-803 shifted the channel's conductance-voltage curve either left or right over a 145-mV range. Since this residue is predicted to be in the first loop of RCK2 these results strongly suggest that this loop plays a critical role in determining the intrinsic equilibrium constant for channel opening, and they support the hypothesis that this loop is part of an interface that mediates conformational coupling between RCK1 and RCK2.
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Affiliation(s)
- Hyun-Ju Kim
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju, Korea
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Taraska JW, Zagotta WN. Structural dynamics in the gating ring of cyclic nucleotide-gated ion channels. Nat Struct Mol Biol 2007; 14:854-60. [PMID: 17694071 DOI: 10.1038/nsmb1281] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Accepted: 06/28/2007] [Indexed: 12/14/2022]
Abstract
For ligand-gated ion channels, the binding of a ligand to an intracellular or extracellular domain generates changes in transmembrane pore-forming helices, which alters ion flow. The molecular mechanism for this allostery, however, remains unknown. Here we explore the structure and conformational rearrangements of the C-terminal gating ring of the cyclic nucleotide-gated channel CNGA1 during activation by cyclic nucleotides with patch-clamp fluorometry. By monitoring fluorescent resonance energy transfer (FRET) between membrane-resident quenchers and fluorophores attached to the channel, we detected no movement orthogonal to the membrane during channel activation. By monitoring FRET between fluorophores within the C-terminal region, we determined that the C-terminal end of the C-linker and the end of the C-helix move apart when channels open. We conclude that during channel activation, a portion of the gating ring moves parallel to the plasma membrane, hinging toward the central axis of the channel.
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Affiliation(s)
- Justin W Taraska
- Department of Physiology and Biophysics, Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA
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42
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Koval OM, Fan Y, Rothberg BS. A role for the S0 transmembrane segment in voltage-dependent gating of BK channels. ACTA ACUST UNITED AC 2007; 129:209-20. [PMID: 17296928 PMCID: PMC2151615 DOI: 10.1085/jgp.200609662] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
BK (Maxi-K) channel activity is allosterically regulated by a Ca2+ sensor, formed primarily by the channel's large cytoplasmic carboxyl tail segment, and a voltage sensor, formed by its transmembrane helices. As with other voltage-gated K channels, voltage sensing in the BK channel is accomplished through interactions of the S1–S4 transmembrane segments with the electric field. However, the BK channel is unique in that it contains an additional amino-terminal transmembrane segment, S0, which is important in the functional interaction between BK channel α and β subunits. In this study, we used perturbation mutagenesis to analyze the role of S0 in channel gating. Single residues in the S0 region of the BK channel were substituted with tryptophan to give a large change in side chain volume; native tryptophans in S0 were substituted with alanine. The effects of the mutations on voltage- and Ca2+-dependent gating were quantified using patch-clamp electrophysiology. Three of the S0 mutants (F25W, L26W, and S29W) showed especially large shifts in their conductance–voltage (G-V) relations along the voltage axis compared to wild type. The G-V shifts for these mutants persisted at nominally 0 Ca2+, suggesting that these effects cannot arise simply from altered Ca2+ sensitivity. The basal open probabilities for these mutants at hyperpolarized voltages (where voltage sensor activation is minimal) were similar to wild type, suggesting that these mutations may primarily perturb voltage sensor function. Further analysis using the dual allosteric model for BK channel gating showed that the major effects of the F25W, L26W, and S29W mutations could be accounted for primarily by decreasing the equilibrium constant for voltage sensor movement. We conclude that S0 may make functional contact with other transmembrane regions of the BK channel to modulate the equilibrium between resting and active states of the channel's voltage sensor.
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Affiliation(s)
- Olga M Koval
- Department of Physiology, University of Texas Health Science Center at San Antonio, TX 78229, USA
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43
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Affiliation(s)
- Lawrence Salkoff
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
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44
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Mubagwa K, Gwanyanya A, Zakharov S, Macianskiene R. Regulation of cation channels in cardiac and smooth muscle cells by intracellular magnesium. Arch Biochem Biophys 2007; 458:73-89. [PMID: 17123458 DOI: 10.1016/j.abb.2006.10.014] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2006] [Revised: 10/16/2006] [Accepted: 10/16/2006] [Indexed: 01/06/2023]
Abstract
Magnesium regulates various ion channels in many tissues, including those of the cardiovascular system. General mechanisms by which intracellular Mg(2+) (Mg(i)(2+)) regulates channels are presented. These involve either a direct interaction with the channel, or an indirect modification of channel function via other proteins, such as enzymes or G proteins, or via membrane surface charges and phospholipids. To provide an insight into the role of Mg(i)(2+) in the cardiovascular system, effects of Mg(i)(2+) on major channels in cardiac and smooth muscle cells and the underlying mechanisms are then reviewed. Although Mg(i)(2+) concentrations are known to be stable, conditions under which they may change exist, such as following stimulation of beta-adrenergic receptors and of insulin receptors, or during pathophysiological conditions such as ischemia, heart failure or hypertension. Modifications of cardiovascular electrical or mechanical function, possibly resulting in arrhythmias or hypertension, may result from such changes of Mg(i)(2+) and their effects on cation channels.
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Affiliation(s)
- Kanigula Mubagwa
- Division of Experimental Cardiac Surgery, Department of Heart and Vessel Diseases, Katholieke Universiteit Leuven, Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
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45
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Qian X, Niu X, Magleby KL. Intra- and intersubunit cooperativity in activation of BK channels by Ca2+. ACTA ACUST UNITED AC 2007; 128:389-404. [PMID: 17001085 PMCID: PMC2151572 DOI: 10.1085/jgp.200609486] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The activation of BK channels by Ca(2+) is highly cooperative, with small changes in intracellular Ca(2+) concentration having large effects on open probability (Po). Here we examine the mechanism of cooperative activation of BK channels by Ca(2+). Each of the four subunits of BK channels has a large intracellular COOH terminus with two different high-affinity Ca(2+) sensors: an RCK1 sensor (D362/D367) located on the RCK1 (regulator of conductance of K(+)) domain and a Ca-bowl sensor located on or after the RCK2 domain. To determine interactions among these Ca(2+) sensors, we examine channels with eight different configurations of functional high-affinity Ca(2+) sensors on the four subunits. We find that the RCK1 sensor and Ca bowl contribute about equally to Ca(2+) activation of the channel when there is only one high-affinity Ca(2+) sensor per subunit. We also find that an RCK1 sensor and a Ca bowl on the same subunit are much more effective in increasing Po than when they are on different subunits, indicating positive intrasubunit cooperativity. If it is assumed that BK channels have a gating ring similar to MthK channels with alternating RCK1 and RCK2 domains and that the Ca(2+) sensors act at the flexible (rather than fixed) interfaces between RCK domains, then a comparison of the distribution of Ca(2+) sensors with the observed responses suggest that the interface between RCK1 and RCK2 domains on the same subunit is flexible. On this basis, intrasubunit cooperativity arises because two high-affinity Ca(2+) sensors acting across a flexible interface are more effective in opening the channel than when acting at separate interfaces. An allosteric model incorporating intrasubunit cooperativity nested within intersubunit cooperativity could approximate the Po vs. Ca(2+) response for eight possible subunit configurations of the high-affinity Ca(2+) sensors as well as for three additional configurations from a previous study.
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Affiliation(s)
- Xiang Qian
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL 33101, USA.
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46
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Salkoff L, Butler A, Ferreira G, Santi C, Wei A. High-conductance potassium channels of the SLO family. Nat Rev Neurosci 2007; 7:921-31. [PMID: 17115074 DOI: 10.1038/nrn1992] [Citation(s) in RCA: 409] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
High-conductance, 'big' potassium (BK) channels encoded by the Slo gene family are among the largest and most complex of the extended family of potassium channels. The family of SLO channels apparently evolved from voltage-dependent potassium channels, but acquired a large conserved carboxyl extension, which allows channel gating to be altered in response to the direct sensing of several different intracellular ions, and by other second-messenger systems, such as those activated following neurotransmitter binding to G-protein-coupled receptors (GPCRs). This versatility has been exploited to serve many cellular roles, both within and outside the nervous system.
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Affiliation(s)
- Lawrence Salkoff
- Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euclid Avenue, Saint Louis, Missouri 63110, USA.
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47
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Zeng H, Weiger TM, Fei H, Levitan IB. Mechanisms of two modulatory actions of the channel-binding protein Slob on the Drosophila Slowpoke calcium-dependent potassium channel. ACTA ACUST UNITED AC 2006; 128:583-91. [PMID: 17074977 PMCID: PMC2151581 DOI: 10.1085/jgp.200609653] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Slob57 is an ion channel auxiliary protein that binds to and modulates the Drosophila Slowpoke calcium-dependent potassium channel (dSlo). We reported recently that residues 1–39 of Slob57 comprise the key domain that both causes dSlo inactivation and shifts its voltage dependence of activation to more depolarized voltages. In the present study we show that removal of residues 2–6 from Slob57 abolishes the inactivation, but the ability of Slob57 to rightward shift the voltage dependence of activation of dSlo remains. A synthetic peptide corresponding in sequence to residues 1–6 of Slob57 blocks dSlo in a voltage- and dose-dependent manner. Two Phe residues and at least one Lys residue in this peptide are required for the blocking action. These data indicate that the amino terminus of Slob57 directly blocks dSlo, thereby leading to channel inactivation. Further truncation to residue Arg16 eliminates the modulation of voltage dependence of activation. Thus these two modulatory actions of Slob57 are independent. Mutation within the calcium bowl of dSlo greatly reduces its calcium sensitivity (Bian, S., I. Favre, and E. Moczydlowski. 2001. Proc. Natl. Acad. Sci. USA. 98:4776–4781). We found that Slob57 still causes inactivation of this mutant channel, but does not shift its voltage dependence of activation. This result confirms further the independence of the inactivation and the voltage shift produced by Slob57. It also suggests that the voltage shift requires high affinity Ca2+ binding to an intact calcium bowl. Furthermore, Slob57 inhibits the shift in the voltage dependence of activation of dSlo evoked by Ca2+, and this inhibition by Slob57 is greater at higher free Ca2+ concentrations. These results implicate distinct calcium-dependent and -independent mechanisms in the modulation of dSlo by Slob.
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Affiliation(s)
- Haoyu Zeng
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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48
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Abstract
The mouse Slo3 gene (KCNMA3) encodes a K(+) channel that is regulated by changes in cytosolic pH. Like Slo1 subunits responsible for the Ca(2+) and voltage-activated BK-type channel, the Slo3 alpha subunit contains a pore module with homology to voltage-gated K(+) channels and also an extensive cytosolic C terminus thought to be responsible for ligand dependence. For the Slo3 K(+) channel, increases in cytosolic pH promote channel activation, but very little is known about many fundamental properties of Slo3 currents. Here we define the dependence of macroscopic conductance on voltage and pH and, in particular, examine Slo3 conductance activated at negative potentials. Using this information, the ability of a Horrigan-Aldrich-type of general allosteric model to account for Slo3 gating is examined. Finally, the pH and voltage dependence of Slo3 activation and deactivation kinetics is reported. The results indicate that Slo3 differs from Slo1 in several important ways. The limiting conductance activated at the most positive potentials exhibits a pH-dependent maximum, suggesting differences in the limiting open probability at different pH. Furthermore, over a 600 mV range of voltages (-300 to +300 mV), Slo3 conductance shifts only about two to three orders of magnitude, and the limiting conductance at negative potentials is relatively voltage independent compared to Slo1. Within the context of the Horrigan-Aldrich model, these results indicate that the intrinsic voltage dependence (z(L)) of the Slo3 closed-open equilibrium and the coupling (D) between voltage sensor movement are less than in Slo1. The kinetic behavior of Slo3 currents also differs markedly from Slo1. Both activation and deactivation are best described by two exponential components, both of which are only weakly voltage dependent. Qualitatively, the properties of the two kinetic components in the activation time course suggest that increases in pH increase the fraction of more rapidly opening channels.
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Affiliation(s)
- Xue Zhang
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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49
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Kim HJ, Lim HH, Rho SH, Eom SH, Park CS. Hydrophobic interface between two regulators of K+ conductance domains critical for calcium-dependent activation of large conductance Ca2+-activated K+ channels. J Biol Chem 2006; 281:38573-81. [PMID: 17040919 DOI: 10.1074/jbc.m604769200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
It has been suggested that the large conductance Ca(2)+-activated K(+) channel contains one or more domains known as regulators of K(+) conductance (RCK) in its cytosolic C terminus. Here, we show that the second RCK domain (RCK2) is functionally important and that it forms a heterodimer with RCK1 via a hydrophobic interface. Mutant channels lacking RCK2 are nonfunctional despite their tetramerization and surface expression. The hydrophobic residues that are expected to form an interface between RCK1 and RCK2, based on the crystal structure of the bacterial MthK channel, are well conserved, and the interactions of these residues were confirmed by mutant cycle analysis. The hydrophobic interaction appears to be critical for the Ca(2+)-dependent gating of the large conductance Ca(2+)-activated K(+) channel.
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Affiliation(s)
- Hyun-Ju Kim
- Department of Life Science and Research Center for Biomolecular Nanotechnology, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju 500-712, Korea
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50
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Yu JY, Upadhyaya AB, Atkinson NS. Tissue-specific alternative splicing of BK channel transcripts in Drosophila. GENES BRAIN AND BEHAVIOR 2006; 5:329-39. [PMID: 16716202 DOI: 10.1111/j.1601-183x.2005.00164.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BK-type calcium-activated potassium channels are large conductance channels that respond to changes in intracellular calcium and membrane potential. These channels are used in a wide variety of cell types and have recently been linked to drug sensitivity and tolerance. In both Drosophila and mammals, BK channels are encoded by the slowpoke gene. The Drosophila slowpoke gene includes 14 alternative exons distributed among five sites of alternative splicing. Presumably, the purpose of alternative processing is to provide transcripts tailored to the needs of the cell. The slowpoke gene is expressed in nervous, muscle and epithelial tissues. To determine whether splicing is controlled in a tissue- and/or developmental-specific manner, we built tissue- and developmental-specific cDNA libraries that preserved the relative frequency of various slowpoke splice variants. These libraries were screened by colony hybridization using alternative exon-specific DNA probes to document the frequency of individual alternative exons in different developmental stages and distinct tissue types. We demonstrate that slowpoke transcripts undergo tissue- and developmental-specific splicing in Drosophila and some exons are diagnostic for specific tissues.
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Affiliation(s)
- J Y Yu
- Section of Neurobiology, The University of Texas at Austin, Austin, TX 78712-0248, USA
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