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Nakajo K, Kasuya G. Modulation of potassium channels by transmembrane auxiliary subunits via voltage-sensing domains. Physiol Rep 2024; 12:e15980. [PMID: 38503563 PMCID: PMC10950684 DOI: 10.14814/phy2.15980] [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: 12/29/2023] [Revised: 03/07/2024] [Accepted: 03/07/2024] [Indexed: 03/21/2024] Open
Abstract
Voltage-gated K+ (KV ) and Ca2+ -activated K+ (KCa ) channels are essential proteins for membrane repolarization in excitable cells. They also play important physiological roles in non-excitable cells. Their diverse physiological functions are in part the result of their auxiliary subunits. Auxiliary subunits can alter the expression level, voltage dependence, activation/deactivation kinetics, and inactivation properties of the bound channel. KV and KCa channels are activated by membrane depolarization through the voltage-sensing domain (VSD), so modulation of KV and KCa channels through the VSD is reasonable. Recent cryo-EM structures of the KV or KCa channel complex with auxiliary subunits are shedding light on how these subunits bind to and modulate the VSD. In this review, we will discuss four examples of auxiliary subunits that bind directly to the VSD of KV or KCa channels: KCNQ1-KCNE3, Kv4-DPP6, Slo1-β4, and Slo1-γ1. Interestingly, their binding sites are all different. We also present some examples of how functionally critical binding sites can be determined by introducing mutations. These structure-guided approaches would be effective in understanding how VSD-bound auxiliary subunits modulate ion channels.
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Affiliation(s)
- Koichi Nakajo
- Division of Integrative Physiology, Department of PhysiologyJichi Medical UniversityShimotsukeJapan
| | - Go Kasuya
- Division of Integrative Physiology, Department of PhysiologyJichi Medical UniversityShimotsukeJapan
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2
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Moldenhauer HJ, Dinsdale RL, Alvarez S, Fernández-Jaén A, Meredith AL. Effect of an autism-associated KCNMB2 variant, G124R, on BK channel properties. Curr Res Physiol 2022; 5:404-413. [PMID: 36203817 PMCID: PMC9531041 DOI: 10.1016/j.crphys.2022.09.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Revised: 08/26/2022] [Accepted: 09/20/2022] [Indexed: 11/30/2022] Open
Abstract
BK K+ channels are critical regulators of neuron and muscle excitability, comprised of a tetramer of pore-forming αsubunits from the KCNMA1 gene and cell- and tissue-selective β subunits (KCNMB1-4). Mutations in KCNMA1 are associated with neurological disorders, including autism. However, little is known about the role of neuronal BK channel β subunits in human neuropathology. The β2 subunit is expressed in central neurons and imparts inactivation to BK channels, as well as altering activation and deactivation gating. In this study, we report the functional effect of G124R, a novel KCNMB2 mutation obtained from whole-exome sequencing of a patient diagnosed with autism spectrum disorder. Residue G124, located in the extracellular loop between TM1 and TM2, is conserved across species, and the G124R missense mutation is predicted deleterious with computational tools. To investigate the pathogenicity potential, BK channels were co-expressed with β2WT and β2G124R subunits in HEK293T cells. BK/β2 currents were assessed from inside-out patches under physiological K+ conditions (140/6 mM K+ and 10 μM Ca2+) during activation and inactivation (voltage-dependence and kinetics). Using β2 subunits lacking inactivation (β2IR) revealed that currents from BK/β2IRG124R channels activated 2-fold faster and deactivated 2-fold slower compared with currents from BK/β2IRWT channels, with no change in the voltage-dependence of activation (V1/2). Despite the changes in the BK channel opening and closing, BK/β2G124R inactivation rates (τinact and τrecovery), and the V1/2 of inactivation, were unaltered compared with BK/β2WT channels under standard steady-state voltage protocols. Action potential-evoked current was also unchanged. Thus, the mutant phenotype suggests the β2G124R TM1-TM2 extracellular loop could regulate BK channel activation and deactivation kinetics. However, additional evidence is needed to validate pathogenicity for this patient-associated variant in KCNMB2. KCNMA1 channelopathy is a neurobehavioral disorder associated with seizures, dyskinesia, and intellectual disability. KCNMB2 encodes an accessory β subunit that confers inactivation to the KCNMA1 pore-forming α subunit BK channel. The KCNMB2-G124R variant, identified in an autistic individual, affects BK/β2 channel activation but not inactivation.
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Affiliation(s)
- Hans J. Moldenhauer
- Dept. of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Ria L. Dinsdale
- Dept. of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | | | - Alberto Fernández-Jaén
- Dept. of Pediatric Neurology, Hospital Universitario Quirónsalud, School of Medicine, Universidad Europea de, Madrid, Spain
| | - Andrea L. Meredith
- Dept. of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Corresponding author. Dept. of Physiology University of Maryland School of Medicine, 655 W. Baltimore St. Baltimore, MD, 21201, USA.
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3
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Martín P, Moncada M, Castillo K, Orsi F, Ducca G, Fernández-Fernández JM, González C, Milesi V. Arachidonic acid effect on the allosteric gating mechanism of BK (Slo1) channels associated with the β1 subunit. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183550. [PMID: 33417967 DOI: 10.1016/j.bbamem.2021.183550] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 12/04/2020] [Accepted: 12/30/2020] [Indexed: 11/30/2022]
Abstract
Arachidonic acid (AA) is a fatty acid involved in the modulation of several ion channels. Previously, we reported that AA activates the high conductance Ca2+- and voltage-dependent K+ channel (BK) in vascular smooth muscle depending on the expression of the auxiliary β1 subunit. Here, using the patch-clamp technique on BK channel co-expressed with β1 subunit in a heterologous cell expression system, we analyzed whether AA modifies the three functional modules involved in the channel gating: the voltage sensor domain (VSD), the pore domain (PD), and the intracellular calcium sensor domain (CSD). We present evidence that AA activates BK channel in a direct way, inducing VSD stabilization on its active configuration observed as a significant left shift in the Q-V curve obtained from gating currents recordings. Moreover, AA facilitates the channel opening transitions when VSD are at rest, and the CSD are unoccupied. Furthermore, the activation was independent of the intracellular Ca2+ concentration and reduced when the BK channel was co-expressed with the Y74A mutant of the β1 subunit. These results allow us to present new insigths in the mechanism by which AA modulates BK channels co-expressed with its auxiliary β1 subunit.
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Affiliation(s)
- Pedro Martín
- Instituto de Estudios Inmunológicos y Fisiopatológicos (IIFP), UNLP, CONICET, asociado CIC PBA, Facultad de Ciencias Exactas, La Plata, Argentina.
| | - Melisa Moncada
- Instituto de Estudios Inmunológicos y Fisiopatológicos (IIFP), UNLP, CONICET, asociado CIC PBA, Facultad de Ciencias Exactas, La Plata, Argentina.
| | - Karen Castillo
- CINV: Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
| | - Federico Orsi
- Instituto de Estudios Inmunológicos y Fisiopatológicos (IIFP), UNLP, CONICET, asociado CIC PBA, Facultad de Ciencias Exactas, La Plata, Argentina.
| | - Gerónimo Ducca
- Instituto de Estudios Inmunológicos y Fisiopatológicos (IIFP), UNLP, CONICET, asociado CIC PBA, Facultad de Ciencias Exactas, La Plata, Argentina.
| | - José Manuel Fernández-Fernández
- Laboratory of Molecular Physiology, Department of Experimental and Health Sciences, University Pompeu Fabra, 08003 Barcelona, Spain.
| | - Carlos González
- CINV: Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
| | - Verónica Milesi
- Instituto de Estudios Inmunológicos y Fisiopatológicos (IIFP), UNLP, CONICET, asociado CIC PBA, Facultad de Ciencias Exactas, La Plata, Argentina.
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4
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Tao X, MacKinnon R. Molecular structures of the human Slo1 K + channel in complex with β4. eLife 2019; 8:51409. [PMID: 31815672 PMCID: PMC6934384 DOI: 10.7554/elife.51409] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 12/06/2019] [Indexed: 12/16/2022] Open
Abstract
Slo1 is a Ca2+- and voltage-activated K+ channel that underlies skeletal and smooth muscle contraction, audition, hormone secretion and neurotransmitter release. In mammals, Slo1 is regulated by auxiliary proteins that confer tissue-specific gating and pharmacological properties. This study presents cryo-EM structures of Slo1 in complex with the auxiliary protein, β4. Four β4, each containing two transmembrane helices, encircle Slo1, contacting it through helical interactions inside the membrane. On the extracellular side, β4 forms a tetrameric crown over the pore. Structures with high and low Ca2+ concentrations show that identical gating conformations occur in the absence and presence of β4, implying that β4 serves to modulate the relative stabilities of 'pre-existing' conformations rather than creating new ones. The effects of β4 on scorpion toxin inhibition kinetics are explained by the crown, which constrains access but does not prevent binding.
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Affiliation(s)
- Xiao Tao
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, Howard Hughes Medical Institute, New York, United States
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, Howard Hughes Medical Institute, New York, United States
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Xin F, Cheng Y, Ren J, Zhang S, Liu P, Zhao H, Huang H, Wang W. The extracellular loop of the auxiliary β1-subunit is involved in the regulation of BKCa channel mechanosensitivity. Am J Physiol Cell Physiol 2018; 315:C485-C493. [DOI: 10.1152/ajpcell.00037.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The large conductance Ca2+-activated potassium (BKCa) channel is activated by stretch. The stress-regulated exon (STREX) in α-subunits is known to affect the mechanosensitivity of BKCa channels. However, in human colonic smooth muscle cells (HCoSMCs), we found that the α-subunits without STREX (ZERO-BK) and β1-subunits could be detected yet the cells were mechanosensitive. Whether the β1-subunit is involved in the regulation of BKCa mechanosensitivity is unclear. In the present study, ZERO-BK and β1-subunits were individually expressed or coexpressed in HEK293 cells and cell-attached patch-clamp techniques were used to measure BKCa currents defining mechanosensitivity. Single-channel patch-clamp recordings from HEK293 cells cotransfected with ZERO-BK and β1-subunits showed stretch sensitivity, but there was no mechanosensitivity in HEK293 cells transfected only with ZERO-BK. We also showed that expression of the β1-subunit could increase mechanosensitivity of the STREX-type α-subunits (STREX-BK). To identify the domain in β1-subunits responsible for affecting stretch sensitivity, we expressed β1- LoopDel (chimeric β1-subunits without the extracellular loop) or β1- C TermDel (chimeric β1-subunits without COOH terminus) with ZERO-BK in HEK293 cells. The data showed that deletion of the extracellular loop but not the COOH terminus of β1-subunits virtually abolished the mechanosensitivity. These results suggest that the extracellular loop of the β1-subunit is involved in the regulation of BKCa channel mechanosensitivity and that role is independent of STREX.
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Affiliation(s)
- Fang Xin
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
| | - Yuan Cheng
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
| | - Jie Ren
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
- Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Capital Medical University, Beijing, People’s Republic of China
| | - Sitao Zhang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
| | - Ping Liu
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
| | - Haiyan Zhao
- Yanjing Medical College, Capital Medical University, Beijing, People’s Republic of China
| | - Haixia Huang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
- Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Capital Medical University, Beijing, People’s Republic of China
| | - Wei Wang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
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6
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Kuntamallappanavar G, Dopico AM. BK β1 subunit-dependent facilitation of ethanol inhibition of BK current and cerebral artery constriction is mediated by the β1 transmembrane domain 2. Br J Pharmacol 2017; 174:4430-4448. [PMID: 28940182 DOI: 10.1111/bph.14046] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 09/11/2017] [Accepted: 09/14/2017] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Ethanol at concentrations obtained in the circulation during moderate-heavy episodic drinking (30-60 mM) causes cerebral artery constriction in several species, including humans. In rodents, ethanol-induced cerebral artery constriction results from ethanol inhibition of large conductance voltage/Ca2+i -gated K+ (BK) channels in cerebral artery myocytes. Moreover, the smooth muscle-abundant BK β1 accessory subunit is required for ethanol to inhibit cerebral artery myocyte BK channels under physiological Ca2+i and voltages and thus constrict cerebral arteries. The molecular bases of these ethanol actions remain unknown. Here, we set to identify the BK β1 region(s) that mediates ethanol-induced inhibition of cerebral artery myocyte BK channels and eventual arterial constriction. EXPERIMENTAL APPROACH We used protein biochemistry, patch-clamp on engineered channel subunits, reversible cDNA permeabilization of KCNMB1 K/O mouse arteries and artery in vitro pressurization. KEY RESULTS Ethanol inhibition of BK current was facilitated by β1 but not β4 subunits. Furthermore, only BK complexes containing β chimeras with β1 transmembrane (TM) domains on a β4 background or with a β1 TM2 domain on a β4 background displayed ethanol responses identical to those of BK complexes including wild-type β1. Moreover, β1 TM2 itself but not other β regions were necessary for ethanol-induced cerebral artery constriction. CONCLUSIONS AND IMPLICATIONS BK β1 TM2 is necessary for this subunit to enable ethanol-induced inhibition of myocyte BK channels and cerebral artery constriction at physiological Ca2+ and voltages. Thus, novel agents that target β1 TM2 may be considered to counteract ethanol-induced cerebral artery constriction and associated cerebrovascular conditions.
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Affiliation(s)
- Guruprasad Kuntamallappanavar
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN, USA
| | - Alex M Dopico
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN, USA
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7
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Han YY, Wang LJ, Zhang L, Zhang WW, Ma KT, Li L, Si JQ. Association between potassium channel SNPs and essential hypertension in Xinjiang Kazak Chinese patients. Exp Ther Med 2017; 14:1999-2006. [PMID: 28962116 PMCID: PMC5609208 DOI: 10.3892/etm.2017.4734] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 05/05/2017] [Indexed: 12/27/2022] Open
Abstract
The aim of the present study was to examine whether single-nucleotide polymorphisms (SNPs) of β1 subunit of large-conductance Ca2+-activated K+ channel (KCNMB1) and inwardly rectifying K+ channel, subfamily J, member-11 (KCNJ11) are associated with essential hypertension (EH) in Xinjiang Kazak Chinese patients. A polymerase chain reaction-restriction fragment length polymorphism technique was applied to detect the distribution of selected alleles and genotype frequencies in a cohort of Xinjiang Kazak Chinese patients. Samples from 267 patients with EH and 259 normotensive (NT) controls were analyzed. An unconditional logistic regression analysis was used to estimate the odds ratio and 95% confidence interval of the risk factors that are associated with the development of EH. Genotype and allele frequency analyses revealed that the frequency of genotypes KCNJ11-rs2285676 and KCNMB1-rs11739136 was not significantly different between the EH and NT groups. Individuals carrying the GG genotype of KCNJ11-rs5219 had a 2.08 times higher risk of having EH than individuals carrying the GA+AA genotype of KCNJ11-rs5219. Furthermore, the G allele frequency of KCNJ11-rs5219 in the EH group was significantly higher than that of the NT group (P=0.048). Additionally, logistic regression analysis revealed that the body weight and GG genotype of KCNJ11-rs5219 were positively associated with EH in Xinjiang Kazak Chinese patients (P<0.01).
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Affiliation(s)
- Yuan-Yuan Han
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Li-Jie Wang
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Liang Zhang
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China.,The Key Laboratory of Xinjiang Endemic and Ethnic Diseases, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Wen-Wen Zhang
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Ke-Tao Ma
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China.,The Key Laboratory of Xinjiang Endemic and Ethnic Diseases, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Li Li
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China.,The Key Laboratory of Xinjiang Endemic and Ethnic Diseases, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China
| | - Jun-Qiang Si
- Department of Physiology, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China.,The Key Laboratory of Xinjiang Endemic and Ethnic Diseases, Medical College of Shihezi University, Shihezi, Xinjiang 832002, P.R. China.,Department of Physiology, Huazhong University of Science and Technology of Basic Medical Sciences, Wuhan, Hubei 430070, P.R. China.,Department of Physiology, Wuhan University School of Basic Medical Sciences, Wuhan, Hubei 430070, P.R. China
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Lorca RA, Ma X, England SK. The unique N-terminal sequence of the BKCa channel α-subunit determines its modulation by β-subunits. PLoS One 2017; 12:e0182068. [PMID: 28750098 PMCID: PMC5531486 DOI: 10.1371/journal.pone.0182068] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 07/12/2017] [Indexed: 11/18/2022] Open
Abstract
Large conductance voltage- and Ca2+-activated K+ (BKCa) channels are essential regulators of membrane excitability in a wide variety of cells and tissues. An important mechanism of modulation of BKCa channel activity is its association with auxiliary subunits. In smooth muscle cells, the most predominant regulatory subunit of BKCa channels is the β1-subunit. We have previously described that BKCa channels with distinctive N-terminal ends (starting with the amino acid sequence MDAL, MSSN or MANG) are differentially modulated by the β1-subunit, but not by the β2. Here we extended our studies to understand how the distinct N-terminal regions differentially modulate channel activity by β-subunits. We recorded inside-out single-channel currents from HEK293T cells co-expressing the BKCa containing three N-terminal sequences with two β1-β2 chimeric constructs containing the extracellular loop of β1 or β2, and the transmembrane and cytoplasmic domains of β2 or β1, respectively. Both β chimeric constructs induced leftward shifts of voltage-activation curves of channels starting with MANG and MDAL, in the presence of 10 or 100 μM intracellular Ca2+. However, MSSN showed no shift of the voltage-activation, at the same Ca2+ concentrations. The presence of the extracellular loop of β1 in the chimera resembled results seen with the full β1 subunit, suggesting that the extracellular region of β1 might be responsible for the lack of modulation observed in MSSN. We further studied a poly-serine stretch present in the N-terminal region of MSSN and observed that the voltage-activation curves of BKCa channels either containing or lacking this poly-serine stretch were leftward shifted by β1-subunit in a similar way. Overall, our results provide further insights into the mechanism of modulation of the different N-terminal regions of the BKCa channel by β-subunits and highlight the extension of this region of the channel as a form of modulation of channel activity.
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Affiliation(s)
- Ramón A. Lorca
- Center for Reproductive Health Sciences, Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, Missouri, United States of America
- * E-mail:
| | - Xiaofeng Ma
- Center for Reproductive Health Sciences, Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Sarah K. England
- Center for Reproductive Health Sciences, Department of Obstetrics and Gynecology, Washington University in St. Louis, St. Louis, Missouri, United States of America
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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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Kuntamallappanavar G, Dopico AM. Alcohol modulation of BK channel gating depends on β subunit composition. J Gen Physiol 2016; 148:419-440. [PMID: 27799321 PMCID: PMC5089933 DOI: 10.1085/jgp.201611594] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 10/14/2016] [Indexed: 01/01/2023] Open
Abstract
In most mammalian tissues, Ca2+i/voltage-gated, large conductance K+ (BK) channels consist of channel-forming slo1 and auxiliary (β1-β4) subunits. When Ca2+i (3-20 µM) reaches the vicinity of BK channels and increases their activity at physiological voltages, β1- and β4-containing BK channels are, respectively, inhibited and potentiated by intoxicating levels of ethanol (50 mM). Previous studies using different slo1s, lipid environments, and Ca2+i concentrations-all determinants of the BK response to ethanol-made it impossible to determine the specific contribution of β subunits to ethanol action on BK activity. Furthermore, these studies measured ethanol action on ionic current under a limited range of stimuli, rendering no information on the gating processes targeted by alcohol and their regulation by βs. Here, we used identical experimental conditions to obtain single-channel and macroscopic currents of the same slo1 channel ("cbv1" from rat cerebral artery myocytes) in the presence and absence of 50 mM ethanol. First, we assessed the role five different β subunits (1,2,2-IR, 3-variant d, and 4) in ethanol action on channel function. Thus, two phenotypes were identified: (1) ethanol potentiated cbv1-, cbv1+β3-, and cbv1+β4-mediated currents at low Ca2+i while inhibiting current at high Ca2+i, the potentiation-inhibition crossover occurring at 20 µM Ca2+i; (2) for cbv1+β1, cbv1+wt β2, and cbv1+β2-IR, this crossover was shifted to ∼3 µM Ca2+i Second, applying Horrigan-Aldrich gating analysis on both phenotypes, we show that ethanol fails to modify intrinsic gating and the voltage-dependent parameters under examination. For cbv1, however, ethanol (a) drastically increases the channel's apparent Ca2+ affinity (nine-times decrease in Kd) and (b) very mildly decreases allosteric coupling between Ca2+ binding and channel opening (C). The decreased Kd leads to increased channel activity. For cbv1+β1, ethanol (a) also decreases Kd, yet this decrease (two times) is much smaller than that of cbv1; (b) reduces C; and (c) decreases coupling between Ca2+ binding and voltage sensing (parameter E). Decreased allosteric coupling leads to diminished BK activity. Thus, we have identified critical gating modifications that lead to the differential actions of ethanol on slo1 with and without different β subunits.
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Affiliation(s)
- Guruprasad Kuntamallappanavar
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN 38103
| | - Alex M Dopico
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN 38103
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11
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Abstract
BK channels are universal regulators of cell excitability, given their exceptional unitary conductance selective for K(+), joint activation mechanism by membrane depolarization and intracellular [Ca(2+)] elevation, and broad expression pattern. In this chapter, we discuss the structural basis and operational principles of their activation, or gating, by membrane potential and calcium. We also discuss how the two activation mechanisms interact to culminate in channel opening. As members of the voltage-gated potassium channel superfamily, BK channels are discussed in the context of archetypal family members, in terms of similarities that help us understand their function, but also seminal structural and biophysical differences that confer unique functional properties.
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Affiliation(s)
- A Pantazis
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States
| | - R Olcese
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States.
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12
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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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13
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Molecular mechanism underlying β1 regulation in voltage- and calcium-activated potassium (BK) channels. Proc Natl Acad Sci U S A 2015; 112:4809-14. [PMID: 25825713 DOI: 10.1073/pnas.1504378112] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Being activated by depolarizing voltages and increases in cytoplasmic Ca(2+), voltage- and calcium-activated potassium (BK) channels and their modulatory β-subunits are able to dampen or stop excitatory stimuli in a wide range of cellular types, including both neuronal and nonneuronal tissues. Minimal alterations in BK channel function may contribute to the pathophysiology of several diseases, including hypertension, asthma, cancer, epilepsy, and diabetes. Several gating processes, allosterically coupled to each other, control BK channel activity and are potential targets for regulation by auxiliary β-subunits that are expressed together with the α (BK)-subunit in almost every tissue type where they are found. By measuring gating currents in BK channels coexpressed with chimeras between β1 and β3 or β2 auxiliary subunits, we were able to identify that the cytoplasmic regions of β1 are responsible for the modulation of the voltage sensors. In addition, we narrowed down the structural determinants to the N terminus of β1, which contains two lysine residues (i.e., K3 and K4), which upon substitution virtually abolished the effects of β1 on charge movement. The mechanism by which K3 and K4 stabilize the voltage sensor is not electrostatic but specific, and the α (BK)-residues involved remain to be identified. This is the first report, to our knowledge, where the regulatory effects of the β1-subunit have been clearly assigned to a particular segment, with two pivotal amino acids being responsible for this modulation.
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14
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Fernández-Mariño AI, Cidad P, Zafra D, Nocito L, Domínguez J, Oliván-Viguera A, Köhler R, López-López JR, Pérez-García MT, Valverde MÁ, Guinovart JJ, Fernández-Fernández JM. Tungstate-targeting of BKαβ1 channels tunes ERK phosphorylation and cell proliferation in human vascular smooth muscle. PLoS One 2015; 10:e0118148. [PMID: 25659150 PMCID: PMC4320054 DOI: 10.1371/journal.pone.0118148] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 01/05/2015] [Indexed: 02/07/2023] Open
Abstract
Despite the substantial knowledge on the antidiabetic, antiobesity and antihypertensive actions of tungstate, information on its primary target/s is scarce. Tungstate activates both the ERK1/2 pathway and the vascular voltage- and Ca2+-dependent large-conductance BKαβ1 potassium channel, which modulates vascular smooth muscle cell (VSMC) proliferation and function, respectively. Here, we have assessed the possible involvement of BKαβ1 channels in the tungstate-induced ERK phosphorylation and its relevance for VSMC proliferation. Western blot analysis in HEK cell lines showed that expression of vascular BKαβ1 channels potentiates the tungstate-induced ERK1/2 phosphorylation in a Gi/o protein-dependent manner. Tungstate activated BKαβ1 channels upstream of G proteins as channel activation was not altered by the inhibition of G proteins with GDPβS or pertussis toxin. Moreover, analysis of Gi/o protein activation measuring the FRET among heterologously expressed Gi protein subunits suggested that tungstate-targeting of BKαβ1 channels promotes G protein activation. Single channel recordings on VSMCs from wild-type and β1-knockout mice indicated that the presence of the regulatory β1 subunit was essential for the tungstate-mediated activation of BK channels in VSMCs. Moreover, the specific BK channel blocker iberiotoxin lowered tungstate-induced ERK phosphorylation by 55% and partially reverted (by 51%) the tungstate-produced reduction of platelet-derived growth factor (PDGF)-induced proliferation in human VSMCs. Our observations indicate that tungstate-targeting of BKαβ1 channels promotes activation of PTX-sensitive Gi proteins to enhance the tungstate-induced phosphorylation of ERK, and inhibits PDGF-stimulated cell proliferation in human vascular smooth muscle.
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Affiliation(s)
- Ana Isabel Fernández-Mariño
- Laboratori de Fisiologia Molecular i Canalopaties, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain
| | - Pilar Cidad
- Departamento de Bioquímica y Biología Molecular y Fisiología and Instituto de Biología y Genética Molecular (IBGM), Universidad de Valladolid and Consejo Superior de Investigaciones Científicas (CSIC), Valladolid, Spain
| | - Delia Zafra
- Institute for Research in Biomedicine (IRB Barcelona) and Department of Biochemistry and Molecular Biology, University of Barcelona, and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas (CIBERDEM), Barcelona, Spain
| | - Laura Nocito
- Institute for Research in Biomedicine (IRB Barcelona) and Department of Biochemistry and Molecular Biology, University of Barcelona, and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas (CIBERDEM), Barcelona, Spain
| | - Jorge Domínguez
- Institute for Research in Biomedicine (IRB Barcelona) and Department of Biochemistry and Molecular Biology, University of Barcelona, and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas (CIBERDEM), Barcelona, Spain
| | - Aida Oliván-Viguera
- Aragon Institute of Health Sciences I+CS/IIS and Fundación Agencia Aragonesa para la Investigación y Desarrollo (ARAID), Zaragoza, Spain
| | - Ralf Köhler
- Aragon Institute of Health Sciences I+CS/IIS and Fundación Agencia Aragonesa para la Investigación y Desarrollo (ARAID), Zaragoza, Spain
| | - José R. López-López
- Departamento de Bioquímica y Biología Molecular y Fisiología and Instituto de Biología y Genética Molecular (IBGM), Universidad de Valladolid and Consejo Superior de Investigaciones Científicas (CSIC), Valladolid, Spain
| | - María Teresa Pérez-García
- Departamento de Bioquímica y Biología Molecular y Fisiología and Instituto de Biología y Genética Molecular (IBGM), Universidad de Valladolid and Consejo Superior de Investigaciones Científicas (CSIC), Valladolid, Spain
| | - Miguel Ángel Valverde
- Laboratori de Fisiologia Molecular i Canalopaties, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain
| | - Joan J. Guinovart
- Institute for Research in Biomedicine (IRB Barcelona) and Department of Biochemistry and Molecular Biology, University of Barcelona, and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas (CIBERDEM), Barcelona, Spain
| | - José M. Fernández-Fernández
- Laboratori de Fisiologia Molecular i Canalopaties, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain
- * E-mail:
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15
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Kuntamallappanavar G, Toro L, Dopico AM. Both transmembrane domains of BK β1 subunits are essential to confer the normal phenotype of β1-containing BK channels. PLoS One 2014; 9:e109306. [PMID: 25275635 PMCID: PMC4183656 DOI: 10.1371/journal.pone.0109306] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/10/2014] [Indexed: 01/03/2023] Open
Abstract
Voltage/Ca2+i-gated, large conductance K+ (BK) channels result from tetrameric association of α (slo1) subunits. In most tissues, BK protein complexes include regulatory β subunits that contain two transmembrane domains (TM1, TM2), an extracellular loop, and two short intracellular termini. Four BK β types have been identified, each presenting a rather selective tissue-specific expression profile. Thus, BK β modifies current phenotype to suit physiology in a tissue-specific manner. The smooth muscle-abundant BK β1 drastically increases the channel's apparent Ca2+i sensitivity. The resulting phenotype is critical for BK channel activity to increase in response to Ca2+ levels reached near the channel during depolarization-induced Ca2+ influx and myocyte contraction. The eventual BK channel activation generates outward K+ currents that drive the membrane potential in the negative direction and eventually counteract depolarization-induced Ca2+ influx. The BK β1 regions responsible for the characteristic phenotype of β1-containing BK channels remain to be identified. We used patch-clamp electrophysiology on channels resulting from the combination of smooth muscle slo1 (cbv1) subunits with smooth muscle-abundant β1, neuron-abundant β4, or chimeras constructed by swapping β1 and β4 regions, and determined the contribution of specific β1 regions to the BK phenotype. At Ca2+ levels found near the channel during myocyte contraction (10 µM), channel complexes that included chimeras having both TMs from β1 and the remaining regions (“background”) from β4 showed a phenotype (Vhalf, τact, τdeact) identical to that of complexes containing wt β1. This phenotype could not be evoked by complexes that included chimeras combining either β1 TM1 or β1 TM2 with a β4 background. Likewise, β “halves” (each including β1 TM1 or β1 TM2) resulting from interrupting the continuity of the EC loop failed to render the normal phenotype, indicating that physical connection between β1 TMs via the EC loop is also necessary for proper channel function.
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Affiliation(s)
- Guruprasad Kuntamallappanavar
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, Tennessee, United States of America
| | - Ligia Toro
- Departments of Anesthesiology and of Molecular and Medical Pharmacology, University of California Los Angeles, David Geffen School of Medicine, Los Angeles, California, United States of America
| | - Alex M. Dopico
- Department of Pharmacology, College of Medicine, The University of Tennessee Health Science Center, Memphis, Tennessee, United States of America
- * E-mail:
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16
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Yuan C, Velázquez-Marrero C, Bernardo A, Treistman SN. Lipids modulate the increase of BK channel calcium sensitivity by the β1 subunit. PLoS One 2014; 9:e107917. [PMID: 25254644 PMCID: PMC4177886 DOI: 10.1371/journal.pone.0107917] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 08/24/2014] [Indexed: 11/18/2022] Open
Abstract
Co-expression of the auxiliary β1 subunit with the pore forming α subunit of BK dramatically alters apparent calcium sensitivity. Investigation of the mechanism underlying the increase in calcium sensitivity of BK in smooth muscle has concentrated on the energetic effect of β1's interaction with α. We take a novel approach, exploring whether β1 modification of calcium sensitivity reflects altered interaction between the channel protein and surrounding lipids. We reconstituted hSlo BK α and BK α+β1 channels into two sets of bilayers. One set contained POPE with POPS, POPG, POPA and POPC, where the length of acyl chains is constant, but surface charge differs. The second set is a series of neutral bilayers formed from DOPE with phosphatidylcholines (PCs) of varying acyl chain lengths: C (14:1), C (18:1), C (22:1) and C (24:1), and with brain sphingomyelin (SPM), in which surface charge is constant, but bilayer thickness varies. The increase in calcium sensitivity caused by the β1 subunit was preserved in negatively charged lipid bilayers but not in neutral bilayers, indicating that modification of apparent Ca(2+) sensitivity by β1 is modulated by membrane lipids, requiring negatively charged lipids in the membrane. Moreover, the presence of β1 reduces BK activity in thin bilayers of PC 14:1 and thick bilayers containing SPM, but has no significant effect on activity of BK in PC 18:1, PC 22:1 and PC 24:1 bilayers. These data suggest that auxiliary β1 subunits fine-tune channel gating not only through direct subunit-subunit interactions but also by modulating lipid-protein interactions.
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Affiliation(s)
- Chunbo Yuan
- Institute of Neurobiology, University of Puerto Rico, San Juan, Puerto Rico
| | | | - Alexandra Bernardo
- Institute of Neurobiology, University of Puerto Rico, San Juan, Puerto Rico
| | - Steven N. Treistman
- Institute of Neurobiology, University of Puerto Rico, San Juan, Puerto Rico
- * E-mail:
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17
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Li M, Chang S, Yang L, Shi J, McFarland K, Yang X, Moller A, Wang C, Zou X, Chi C, Cui J. Conopeptide Vt3.1 preferentially inhibits BK potassium channels containing β4 subunits via electrostatic interactions. J Biol Chem 2014; 289:4735-42. [PMID: 24398688 DOI: 10.1074/jbc.m113.535898] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
BK channel β subunits (β1-β4) modulate the function of channels formed by slo1 subunits to produce tissue-specific phenotypes. The molecular mechanism of how the homologous β subunits differentially alter BK channel functions and the role of different BK channel functions in various physiologic processes remain unclear. By studying channels expressed in Xenopus laevis oocytes, we show a novel disulfide-cross-linked dimer conopeptide, Vt3.1 that preferentially inhibits BK channels containing the β4 subunit, which is most abundantly expressed in brain and important for neuronal functions. Vt3.1 inhibits the currents by a maximum of 71%, shifts the G-V relation by 45 mV approximately half-saturation concentrations, and alters both open and closed time of single channel activities, indicating that the toxin alters voltage dependence of the channel. Vt3.1 contains basic residues and inhibits voltage-dependent activation by electrostatic interactions with acidic residues in the extracellular loops of the slo1 and β4 subunits. These results suggest a large interaction surface between the slo1 subunit of BK channels and the β4 subunit, providing structural insight into the molecular interactions between slo1 and β4 subunits. The results also suggest that Vt3.1 is an excellent tool for studying β subunit modulation of BK channels and for understanding the physiological roles of BK channels in neurophysiology.
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Affiliation(s)
- Min Li
- From the Institute of Protein Research, Tongji University, Shanghai 200092, China
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18
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Hoshi T, Pantazis A, Olcese R. Transduction of voltage and Ca2+ signals by Slo1 BK channels. Physiology (Bethesda) 2013; 28:172-89. [PMID: 23636263 DOI: 10.1152/physiol.00055.2012] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Large-conductance Ca2+ -and voltage-gated K+ channels are activated by an increase in intracellular Ca2+ concentration and/or depolarization. The channel activation mechanism is well described by an allosteric model encompassing the gate, voltage sensors, and Ca2+ sensors, and the model is an excellent framework to understand the influences of auxiliary β and γ subunits and regulatory factors such as Mg2+. Recent advances permit elucidation of structural correlates of the biophysical mechanism.
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Affiliation(s)
- T Hoshi
- Department of Physiology, The University of Pennsylvania, Philadelphia, Pennsylvania, USA
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19
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Fernández-Mariño AI, Valverde MA, Fernández-Fernández JM. BK channel activation by tungstate requires the β1 subunit extracellular loop residues essential to modulate voltage sensor function and channel gating. Pflugers Arch 2013; 466:1365-75. [DOI: 10.1007/s00424-013-1379-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 10/08/2013] [Accepted: 10/08/2013] [Indexed: 02/07/2023]
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20
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The interface between membrane-spanning and cytosolic domains in Ca²+-dependent K+ channels is involved in β subunit modulation of gating. J Neurosci 2013; 33:11253-61. [PMID: 23825428 DOI: 10.1523/jneurosci.0620-13.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Large-conductance, voltage-, and Ca²⁺-dependent K⁺ (BK) channels are broadly expressed in various tissues to modulate neuronal activity, smooth muscle contraction, and secretion. BK channel activation depends on the interactions among the voltage sensing domain (VSD), the cytosolic domain (CTD), and the pore gate domain (PGD) of the Slo1 α-subunit, and is further regulated by accessory β subunits (β1-β4). How β subunits fine-tune BK channel activation is critical to understand the tissue-specific functions of BK channels. Multiple sites in both Slo1 and the β subunits have been identified to contribute to the interaction between Slo1 and the β subunits. However, it is unclear whether and how the interdomain interactions among the VSD, CTD, and PGD are altered by the β subunits to affect channel activation. Here we show that human β1 and β2 subunits alter interactions between bound Mg²⁺ and gating charge R213 and disrupt the disulfide bond formation at the VSD-CTD interface of mouse Slo1, indicating that the β subunits alter the VSD-CTD interface. Reciprocally, mutations in the Slo1 that alter the VSD-CTD interaction can specifically change the effects of the β1 subunit on the Ca²⁺ activation and of the β2 subunit on the voltage activation. Together, our data suggest a novel mechanism by which the β subunits modulated BK channel activation such that a β subunit may interact with the VSD or the CTD and alter the VSD-CTD interface of the Slo1, which enables the β subunit to have effects broadly on both voltage and Ca²⁺-dependent activation.
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21
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Contreras GF, Castillo K, Enrique N, Carrasquel-Ursulaez W, Castillo JP, Milesi V, Neely A, Alvarez O, Ferreira G, González C, Latorre R. A BK (Slo1) channel journey from molecule to physiology. Channels (Austin) 2013; 7:442-58. [PMID: 24025517 DOI: 10.4161/chan.26242] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Calcium and voltage-activated potassium (BK) channels are key actors in cell physiology, both in neuronal and non-neuronal cells and tissues. Through negative feedback between intracellular Ca (2+) and membrane voltage, BK channels provide a damping mechanism for excitatory signals. Molecular modulation of these channels by alternative splicing, auxiliary subunits and post-translational modifications showed that these channels are subjected to many mechanisms that add diversity to the BK channel α subunit gene. This complexity of interactions modulates BK channel gating, modifying the energetic barrier of voltage sensor domain activation and channel opening. Regions for voltage as well as Ca (2+) sensitivity have been identified, and the crystal structure generated by the 2 RCK domains contained in the C-terminal of the channel has been described. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, has been found to be relevant in many physiological processes. This review includes the hallmarks of BK channel biophysics and its physiological impact on specific cells and tissues, highlighting its relationship with auxiliary subunit expression.
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Affiliation(s)
- Gustavo F Contreras
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile; Doctorado en Ciencias mención Neurociencia; Universidad de Valparaíso; Valparaíso, Chile
| | - Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile
| | - Nicolás Enrique
- Grupo de Investigación en Fisiología Vascular (GINFIV); Universidad Nacional de la Plata; La Plata, Argentina
| | - Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile; Doctorado en Ciencias mención Neurociencia; Universidad de Valparaíso; Valparaíso, Chile
| | - Juan Pablo Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile; Facultad de Ciencias; Universidad de Chile; Santiago, Chile
| | - Verónica Milesi
- Grupo de Investigación en Fisiología Vascular (GINFIV); Universidad Nacional de la Plata; La Plata, Argentina
| | - Alan Neely
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile
| | | | - Gonzalo Ferreira
- Laboratorio de Canales Iónicos; Departamento de Biofísica; Facultad de Medicina; Universidad de la República; Montevideo, Uruguay
| | - Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso; Facultad de Ciencias; Universidad de Valparaíso; Valparaíso, Chile
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22
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Wu RS, Liu G, Zakharov SI, Chudasama N, Motoike H, Karlin A, Marx SO. Positions of β2 and β3 subunits in the large-conductance calcium- and voltage-activated BK potassium channel. ACTA ACUST UNITED AC 2013; 141:105-17. [PMID: 23277477 PMCID: PMC3536527 DOI: 10.1085/jgp.201210891] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Large-conductance voltage- and Ca2+-gated K+ channels are negative-feedback regulators of excitability in many cell types. They are complexes of α subunits and of one of four types of modulatory β subunits. These have intracellular N- and C-terminal tails and two transmembrane (TM) helices, TM1 and TM2, connected by an ∼100-residue extracellular loop. Based on endogenous disulfide formation between engineered cysteines (Cys), we found that in β2 and β3, as in β1 and β4, TM1 is closest to αS1 and αS2 and TM2 is closest to αS0. Mouse β3 (mβ3) has seven Cys in its loop, one of which is free, and this Cys readily forms disulfides with Cys substituted in the extracellular flanks of each of αS0–αS6. We identified by elimination mβ3-loop Cys152 as the only free Cys. We inferred the disulfide-bonding pattern of the other six Cys. Using directed proteolysis and fragment sizing, we determined this pattern first among the four loop Cys in β1. These are conserved in β2–β4, which have four additional Cys (eight in total), except that mβ3 has one fewer. In β1, disulfides form between Cys at aligned positions 1 and 8 and between Cys at aligned positions 5 and 6. In mβ3, the free Cys is at position 7; position 2 lacks a Cys present in all other β2–β4; and the disulfide pattern is 1–8, 3–4, and 5–6. Presumably, Cys 2 cross-links to Cys 7 in all other β2–β4. Cross-linking of mβ3 Cys152 to Cys substituted in the flanks of αS0–S5 attenuated the protection against iberiotoxin (IbTX); cross-linking of Cys152 to K296C in the αS6 flank and close to the pore enhanced protection against IbTX. In no case was N-type inactivation by the N-terminal tail of mβ3 perturbed. Although the mβ3 loop can move, its position with Cys152 near αK296, in which it blocks IbTX binding, is likely favored.
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Affiliation(s)
- Roland S Wu
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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23
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Selga E, Pérez-Serra A, Moreno-Asso A, Anderson S, Thomas K, Desai M, Brugada R, Pérez GJ, Scornik FS. Molecular heterogeneity of large-conductance calcium-activated potassium channels in canine intracardiac ganglia. Channels (Austin) 2013; 7:322-8. [PMID: 23807090 PMCID: PMC3989361 DOI: 10.4161/chan.25485] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Large conductance calcium-activated potassium (BK) channels are widely expressed in the nervous system. We have recently shown that principal neurons from canine intracardiac ganglia (ICG) express a paxilline- and TEA-sensitive BK current, which increases neuronal excitability. In the present work, we further explore the molecular constituents of the BK current in canine ICG. We found that the β1 and β4 regulatory subunits are expressed in ICG. Single channel voltage-dependence at different calcium concentrations suggested that association of the BKα with a particular β subunit was not enough to explain the channel activity in this tissue. Indeed, we detected the presence of several splice variants of the BKα subunit. In conclusion, BK channels in canine ICG may result from the arrangement of different BKα splice variants, plus accessory β subunits. The particular combinations expressed in canine IC neurons likely rule the excitatory role of BK current in this tissue.
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Affiliation(s)
- Elisabet Selga
- Cardiovascular Genetics Center; Institut d'Investigació Biomèdica de Girona (IdIBGi); Department of Medical Sciences; School of Medicine; University of Girona (UdG); Girona, Spain
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24
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Niu X, Liu G, Wu RS, Chudasama N, Zakharov SI, Karlin A, Marx SO. Orientations and proximities of the extracellular ends of transmembrane helices S0 and S4 in open and closed BK potassium channels. PLoS One 2013; 8:e58335. [PMID: 23472181 PMCID: PMC3589268 DOI: 10.1371/journal.pone.0058335] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Accepted: 02/02/2013] [Indexed: 11/19/2022] Open
Abstract
The large-conductance potassium channel (BK) α subunit contains a transmembrane (TM) helix S0 preceding the canonical TM helices S1 through S6. S0 lies between S4 and the TM2 helix of the regulatory β1 subunit. Pairs of Cys were substituted in the first helical turns in the membrane of BK α S0 and S4 and in β1 TM2. One such pair, W22C in S0 and W203C in S4, was 95% crosslinked endogenously. Under voltage-clamp conditions in outside-out patches, this crosslink was reduced by DTT and reoxidized by a membrane-impermeant bis-quaternary ammonium derivative of diamide. The rate constants for this reoxidation were not significantly different in the open and closed states of the channel. Thus, these two residues are approximately equally close in the two states. In addition, 90% crosslinking of a second pair, R20C in S0 and W203C in S4, had no effect on the V50 for opening. Taken together, these findings indicate that separation between residues at the extracellular ends of S0 and S4 is not required for voltage-sensor activation. On the contrary, even though W22C and W203C were equally likely to form a disulfide in the activated and deactivated states, relative immobilization by crosslinking of these two residues favored the activated state. Furthermore, the efficiency of recrosslinking of W22C and W203C on the cell surface was greater in the presence of the β1 subunit than in its absence, consistent with β1 acting through S0 to stabilize its immobilization relative to α S4.
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Affiliation(s)
- Xiaowei Niu
- From the Center for Molecular Recognition, Departments of Biochemistry, Physiology, and Neurology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Guoxia Liu
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Roland S. Wu
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Neelesh Chudasama
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Sergey I. Zakharov
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Arthur Karlin
- From the Center for Molecular Recognition, Departments of Biochemistry, Physiology, and Neurology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- * E-mail: (AK); (SOM)
| | - Steven O. Marx
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- * E-mail: (AK); (SOM)
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Nguyen NV, Gruslova A, Kosiba WA, Wang B. Combined single-channel and macroscopic recording techniques to analyze gating mechanisms of the large conductance Ca2+ and voltage activated (BK) potassium channel. Methods Mol Biol 2013; 998:133-47. [PMID: 23529426 DOI: 10.1007/978-1-62703-351-0_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Ion channels are integral membrane proteins that regulate membrane potentials and signaling of cells in response to various stimuli. The patch-clamp technique enables the study of single channels or a population of channels. The macroscopic recording approaches are powerful in revealing population-averaged behaviors of channels both under basal conditions and in response to various stimuli, modulators and drugs. On their own, however, these approaches can be insufficient for determinations of channel gating mechanisms as they do not accurately report channel open probabilities below 10(-2) to 10(-3). This obstacle can be overcome with the use of single-channel recording techniques. Single-channel recording techniques can be applied to one or a few channels to estimate P o over a larger range than macroscopic recordings. The combination of heterologous overexpression of ion channels with macroscopic and single-channel recordings can be applied to hundreds of channels to estimate P o between 1 and 10(-8). Here, we describe practical approaches of single-channel recordings that our laboratory utilizes. We also provide examples where the combined macroscopic and single channel approach can be employed to study gating mechanisms of the BK type, large conductance, Ca(2+) and voltage activated potassium channel in a mammalian expression system. The techniques presented should be generally applicable to the studies of ion channels in heterologous expression systems.
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Affiliation(s)
- Nguyen V Nguyen
- Department of Radiology, University of Miami School of Medicine, Miami, FL, USA
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Sun X, Zaydman MA, Cui J. Regulation of Voltage-Activated K(+) Channel Gating by Transmembrane β Subunits. Front Pharmacol 2012; 3:63. [PMID: 22529812 PMCID: PMC3328208 DOI: 10.3389/fphar.2012.00063] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Accepted: 03/29/2012] [Indexed: 01/15/2023] Open
Abstract
Voltage-activated K+ (KV) channels are important for shaping action potentials and maintaining resting membrane potential in excitable cells. KV channels contain a central pore-gate domain (PGD) surrounded by four voltage-sensing domains (VSDs). The VSDs will change conformation in response to alterations of the membrane potential thereby inducing the opening of the PGD. Many KV channels are heteromeric protein complexes containing auxiliary β subunits. These β subunits modulate channel expression and activity to increase functional diversity and render tissue specific phenotypes. This review focuses on the KV β subunits that contain transmembrane (TM) segments including the KCNE family and the β subunits of large conductance, Ca2+- and voltage-activated K+ (BK) channels. These TM β subunits affect the voltage-dependent activation of KV α subunits. Experimental and computational studies have described the structural location of these β subunits in the channel complexes and the biophysical effects on VSD activation, PGD opening, and VSD–PGD coupling. These results reveal some common characteristics and mechanistic insights into KV channel modulation by TM β subunits.
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Affiliation(s)
- Xiaohui Sun
- Department of Biomedical Engineering, Washington University Saint Louis, MO, USA
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