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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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Yan Z, Hu B, Huang Z, Zhong L, Guo X, Weng A, Xiao F, Zeng W, Zhang Y, Ding J, Hou P. Single Channel Recordings Reveal Differential β2 Subunit Modulations Between Mammalian and Drosophila BKCa(β2) Channels. PLoS One 2016; 11:e0163308. [PMID: 27755549 PMCID: PMC5068790 DOI: 10.1371/journal.pone.0163308] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Accepted: 09/07/2016] [Indexed: 12/23/2022] Open
Abstract
Large-conductance Ca2+- and voltage-activated potassium (BK) channels are widely expressed in tissues. As a voltage and calcium sensor, BK channels play significant roles in regulating the action potential frequency, neurotransmitter release, and smooth muscle contraction. After associating with the auxiliary β2 subunit, mammalian BK(β2) channels (mouse or human Slo1/β2) exhibit enhanced activation and complete inactivation. However, how the β2 subunit modulates the Drosophila Slo1 channel remains elusive. In this study, by comparing the different functional effects on heterogeneous BK(β2) channel, we found that Drosophila Slo1/β2 channel exhibits “paralyzed”-like and incomplete inactivation as well as slow activation. Further, we determined three different modulations between mammalian and Drosophila BK(β2) channels: 1) dSlo1/β2 doesn’t have complete inactivation. 2) β2(K33,R34,K35) delays the dSlo1/Δ3-β2 channel activation. 3) dSlo1/β2 channel has enhanced pre-inactivation than mSlo1/β2 channel. The results in our study provide insights into the different modulations of β2 subunit between mammalian and Drosophila Slo1/β2 channels and structural basis underlie the activation and pre-inactivation of other BK(β) complexes.
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Affiliation(s)
- Zhenzhen Yan
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Bin Hu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Zhigang Huang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Ling Zhong
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, 63130, United States
| | - Xiying Guo
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Anxi Weng
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Feng Xiao
- Key Laboratory of Image Processing and Intelligent Control, Huazhong University of Science and Technology, Ministry of Education, Department of Biomedical Engineering, College of Life Science and Technology, Wuhan, Hubei, China
| | - Wenping Zeng
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Yan Zhang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
| | - Jiuping Ding
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
- * E-mail: (PH); (JD)
| | - Panpan Hou
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, 63130, United States
- * E-mail: (PH); (JD)
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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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Inter-α/β subunits coupling mediating pre-inactivation and augmented activation of BKCa(β2). Sci Rep 2013; 3:1666. [PMID: 23588888 PMCID: PMC3627188 DOI: 10.1038/srep01666] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 03/28/2013] [Indexed: 01/15/2023] Open
Abstract
Large-conductance calcium-activated potassium (BK) channels regulate the electric properties and neurotransmitter release in excitable cells. Its auxiliary β2 subunits not only enhance gating, but also confer inactivation via a short-lived preinactivated state. However, the mechanism of enhancement and preinactivation of BK channels by β2 remains elusive. Using our newly developed methods, we demonstrated that electrostatic forces played a crucial role in forming multiple complementary pairs of binding sites between α and β subunits including a “PI site” required for channel preinactivation, an “E site” enhancing calcium sensitivity and an “ECaB” coupling site transferring force to gate from the Ca2+-bowl via the β2(K33, R34, K35), E site and S6-C linker, independent of another Ca2+ binding site mSlo1(D362,D367). A comprehensive structural model of the BK(β2) complex was reconstructed based on these functional studies, which paves the way for a clearer understanding of the structural mechanisms of activation and preinactivation of other BK(β) complexes.
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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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Wu Y, Xiong Y, Wang S, Yi H, Li H, Pan N, Horrigan FT, Wu Y, Ding J. Intersubunit coupling in the pore of BK channels. J Biol Chem 2009; 284:23353-63. [PMID: 19561088 PMCID: PMC2749109 DOI: 10.1074/jbc.m109.027789] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 06/25/2009] [Indexed: 11/06/2022] Open
Abstract
The structural basis underlying the gating of large conductance Ca(2+)-activated K(+) (BK) channels remains elusive. We found that substitution of Leu-312 in the S6 transmembrane segment of mSlo1 BK channels with hydrophilic amino acids of smaller side-chain volume favored the open state. The sensitivities of channels to calcium and voltage were modified by some mutations and completely abolished by others. Interpretation of the results in terms of an allosteric model suggests that the calcium-insensitive mutants greatly destabilize the closed relative to the open conformation and may also disrupt the allosteric coupling between Ca(2+) or voltage sensors and the gate. Some Phe-315 mutations also favor the open state, suggesting that Leu-312 and Phe-315 may interact in the closed state, forming a major energy barrier that the channel has to overcome to open. Homology modeling and molecular dynamic simulations further support that the side chain of Leu-312 can couple strongly with the aromatic ring of Phe-315 in neighboring subunits (L-F coupling) to maintain the channel closed. Additionally, single-channel recordings indicate that the calcium-insensitive mutants, whose kinetics can be approximately characterized by a two-state closed-open (C-O) model, exhibit nearly 100% open probability under physiological conditions without alterations in single-channel conductance. These findings provide a basis for understanding the structure and gating of the BK channel pore.
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Affiliation(s)
- Ying Wu
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
| | - Yu Xiong
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
| | - Sheng Wang
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
| | - Hong Yi
- the State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China, and
| | - Hui Li
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
| | - Na Pan
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
| | - Frank T. Horrigan
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030
| | - Yingliang Wu
- the State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China, and
| | - Jiuping Ding
- From the Key Laboratory of Molecular Biophysics, Huazhong University of Science and Technology, the Ministry of Education, Wuhan, Hubei 430074, China
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Thompson J, Begenisich T. Mechanistic details of BK channel inhibition by the intermediate conductance, Ca2+-activated K channel. Channels (Austin) 2009; 3:194-204. [PMID: 19574736 DOI: 10.4161/chan.3.3.9043] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Salivary gland acinar cells have two types of Ca(2+)-activated K channels required for fluid secretion: the intermediate conductance (IK1) channel and the large conductance (BK) channel. Activation of IK1 inhibits BK channels including in small, cell-free, excised membrane patches. As a first step toward understanding the mechanism underlying this interaction, we examined its voltage sensitivity. We found that the IK1-induced inhibition of BK channels was only weakly voltage dependent and not accompanied by alteration in BK gating kinetics. These actions of IK1 on BK channels are not consistent with a mechanism whereby activation of IK1 causes a shift of the BK channel's voltage dependence as occurs for many BK modulatory processes. In a search for other clues about the interaction mechanism, we noted that the N-terminus of the IK1 channel shares some chemical features with the N-terminal regions of two BK subunits known to inhibit BK activity by blocking the cytoplasmic end of the BK pore. Thus, we tested the idea that the N-terminus of IK1 channels may act similarly. We found that a peptide derived from the N-terminal region of the IK1 protein blocked BK channels. Significantly, we also found that the activation of IK1 channels competed with block by the N-terminus peptide. Thus, the activation of IK1 channels inhibits BK channels by a mechanism that involves block of the cytoplasmic pore, not an alteration in the voltage dependence of BK gating. The mediator of this cytoplasmic pore block may be the IK1 N-terminus.
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Affiliation(s)
- Jill Thompson
- Department of Pharmacology and Physiology and the Center for Oral Biology, University of Rochester Medical Center, Rochester, NY 14642, USA
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Guo Z, Lv C, Yi H, Xiong Y, Wu Y, Li W, Xu T, Ding J. A residue at the cytoplasmic entrance of BK-type channels regulating single-channel opening by its hydrophobicity. Biophys J 2008; 94:3714-25. [PMID: 18400952 PMCID: PMC2292367 DOI: 10.1529/biophysj.107.120022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Accepted: 12/20/2007] [Indexed: 01/17/2023] Open
Abstract
Single large-conductance calcium-activated K(+) (BK) channels encoded by the mSlo gene usually have synchronous gating, but a Drosophila dSlo (A2/C2/E2/G5/10) splice variant (dSlo1A) exhibits very flickery openings. To probe this difference in gating, we constructed a mutant I323T. This channel exhibits four subconductance levels similar to those of dSlo1A. Rectification of the single-channel current-voltage relation of I323T decreased as [Ca(2+) ](in) increased from 10 to 300 microM. Mutagenesis suggests that the hydrophobicity of the residue at the position is important for the wild-type gating; i.e., increasing hydrophobicity prolongs open duration. Molecular dynamics simulation suggests that four hydrophobic pore-lining residues at position 323 of mSlo act cooperatively in a "shutter-like" mechanism gating the permeation of K(+) ions. Rate-equilibrium free energy relations analysis shows that the four I323 residues in an mSlo channel have a conformation 65% similar to the closed conformation during gating. Based on these observations, we suggest that the appearance of rectification and substates of BK-type channels arise from a reduction of the cooperativity among these four residues and a lower probability of being open.
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Affiliation(s)
- Zhaohua Guo
- Key Laboratory of Molecular Biophysics (Huazhong University of Science and Technology), Ministry of Education, College of Life Science and Technology, Wuhan, Hubei 430074, China
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