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Lorca RA, Prabagaran M, England SK. Functional insights into modulation of BKCa channel activity to alter myometrial contractility. Front Physiol 2014; 5:289. [PMID: 25132821 PMCID: PMC4116789 DOI: 10.3389/fphys.2014.00289] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 07/14/2014] [Indexed: 12/15/2022] Open
Abstract
The large-conductance voltage- and Ca(2+)-activated K(+) channel (BKCa) is an important regulator of membrane excitability in a wide variety of cells and tissues. In myometrial smooth muscle, activation of BKCa plays essential roles in buffering contractility to maintain uterine quiescence during pregnancy and in the transition to a more contractile state at the onset of labor. Multiple mechanisms of modulation have been described to alter BKCa channel activity, expression, and cellular localization. In the myometrium, BKCa is regulated by alternative splicing, protein targeting to the plasma membrane, compartmentation in membrane microdomains, and posttranslational modifications. In addition, interaction with auxiliary proteins (i.e., β1- and β2-subunits), association with G-protein coupled receptor signaling pathways, such as those activated by adrenergic and oxytocin receptors, and hormonal regulation provide further mechanisms of variable modulation of BKCa channel function in myometrial smooth muscle. Here, we provide an overview of these mechanisms of BKCa channel modulation and provide a context for them in relation to myometrial function.
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Affiliation(s)
- Ramón A Lorca
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Monali Prabagaran
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Sarah K England
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
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Peng Z, Sakai Y, Kurgan L, Sokolowski B, Uversky V. Intrinsic disorder in the BK channel and its interactome. PLoS One 2014; 9:e94331. [PMID: 24727949 PMCID: PMC3984161 DOI: 10.1371/journal.pone.0094331] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 03/12/2014] [Indexed: 11/18/2022] Open
Abstract
The large-conductance Ca2+-activated K+ (BK) channel is broadly expressed in various mammalian cells and tissues such as neurons, skeletal and smooth muscles, exocrine cells, and sensory cells of the inner ear. Previous studies suggest that BK channels are promiscuous binders involved in a multitude of protein-protein interactions. To gain a better understanding of the potential mechanisms underlying BK interactions, we analyzed the abundance, distribution, and potential mechanisms of intrinsic disorder in 27 BK channel variants from mouse cochlea, 104 previously reported BK-associated proteins (BKAPS) from cytoplasmic and membrane/cytoskeletal regions, plus BK β- and γ-subunits. Disorder was evaluated using the MFDp algorithm, which is a consensus-based predictor that provides a strong and competitive predictive quality and PONDR, which can determine long intrinsically disordered regions (IDRs). Disorder-based binding sites or molecular recognition features (MoRFs) were found using MoRFpred and ANCHOR. BKAP functions were categorized based on Gene Ontology (GO) terms. The analyses revealed that the BK variants contain a number of IDRs. Intrinsic disorder is also common in BKAPs, of which ∼5% are completely disordered. However, intrinsic disorder is very differently distributed within BK and its partners. Approximately 65% of the disordered segments in BK channels are long (IDRs) (>50 residues), whereas >60% of the disordered segments in BKAPs are short IDRs that range in length from 4 to 30 residues. Both α and γ subunits showed various amounts of disorder as did hub proteins of the BK interactome. Our analyses suggest that intrinsic disorder is important for the function of BK and its BKAPs. Long IDRs in BK are engaged in protein-protein and protein-ligand interactions, contain multiple post-translational modification sites, and are subjected to alternative splicing. The disordered structure of BK and its BKAPs suggests one of the underlying mechanisms of their interaction.
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Affiliation(s)
- Zhenling Peng
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Yoshihisa Sakai
- Department of Otolaryngology - Head and Neck Surgery, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Lukasz Kurgan
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Bernd Sokolowski
- Department of Otolaryngology - Head and Neck Surgery, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Vladimir Uversky
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States of America; Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia; Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow Region, Russia
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Jeffries O, Tian L, McClafferty H, Shipston MJ. An electrostatic switch controls palmitoylation of the large conductance voltage- and calcium-activated potassium (BK) channel. J Biol Chem 2011; 287:1468-77. [PMID: 22084244 PMCID: PMC3256903 DOI: 10.1074/jbc.m111.224840] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Protein palmitoylation is a major dynamic posttranslational regulator of protein function. However, mechanisms that control palmitoylation are poorly understood. In many proteins, palmitoylation occurs at cysteine residues juxtaposed to membrane-anchoring domains such as transmembrane helices, sites of irreversible lipid modification, or hydrophobic and/or polybasic domains. In particular, polybasic domains represent an attractive mechanism to dynamically control protein palmitoylation, as the function of these domains can be dramatically influenced by protein phosphorylation. Here we demonstrate that a polybasic domain immediately upstream of palmitoylated cysteine residues within an alternatively spliced insert in the C terminus of the large conductance calcium- and voltage-activated potassium channel is an important determinant of channel palmitoylation and function. Mutation of basic amino acids to acidic residues within the polybasic domain results in inhibition of channel palmitoylation and a significant right-shift in channel half maximal voltage for activation. Importantly, protein kinase A-dependent phosphorylation of a single serine residue within the core of the polybasic domain, which results in channel inhibition, also reduces channel palmitoylation. These data demonstrate the key role of the polybasic domain in controlling stress-regulated exon palmitoylation and suggests that phosphorylation controls the domain by acting as an electrostatic switch.
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Affiliation(s)
- Owen Jeffries
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
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Alternatively spliced domains interact to regulate BK potassium channel gating. Proc Natl Acad Sci U S A 2011; 108:20784-9. [PMID: 22049343 DOI: 10.1073/pnas.1116795108] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Most human genes contain multiple alternative splice sites believed to extend the complexity and diversity of the proteome. However, little is known about how interactions among alternative exons regulate protein function. We used the Caenorhabditis elegans slo-1 large-conductance calcium and voltage-activated potassium (BK) channel gene, which contains three alternative splice sites (A, B, and C) and encodes at least 12 splice variants, to investigate the functional consequences of alternative splicing. These splice sites enable the insertion of exons encoding part of the regulator of K(+) conductance (RCK)1 Ca(2+) coordination domain (exons A1 and A2) and portions of the RCK1-RCK2 linker (exons B0, B1, B2, C0, and C1). Exons A1 and A2 are used in a mutually exclusive manner and are 67% identical. The other exons can extend the RCK1-RCK2 linker by up to 41 residues. Electrophysiological recordings of all isoforms show that the A1 and A2 exons regulate activation kinetics and Ca(2+) sensitivity, but only if alternate exons are inserted at site B or C. Thus, RCK1 interacts with the RCK1-RCK2 linker, and the effect of exon variation on gating depends on the combination of alternate exons present in each isoform.
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Poulsen AN, Jansen-Olesen I, Olesen J, Klaerke DA. Neuronal fast activating and meningeal silent modulatory BK channel splice variants cloned from rat. Pflugers Arch 2010; 461:65-75. [PMID: 20938677 DOI: 10.1007/s00424-010-0887-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Revised: 09/20/2010] [Accepted: 09/23/2010] [Indexed: 12/25/2022]
Abstract
The big conductance calcium-activated K(+) channel (BK) is involved in regulating neuron and smooth muscle cell excitability. Functional diversity of BK is generated by alpha-subunit splice variation and co-expression with beta subunits. Here, we present six different splice combinations cloned from rat brain or cerebral vascular/meningeal tissues, of which at least three variants were previously uncharacterized (X1, X2(92), and X2(188)). An additional variant was identified by polymerase chain reaction but not cloned. Expression in Xenopus oocytes showed that the brain-specific X1 variant displays reduced current, faster activation, and less voltage sensitivity than the insert-less Zero variant. Other cloned variants Strex and Slo27,3 showed slower activation than Zero. The X1 variant contains sequence inserts in the S1-S2 extracellular loop (8 aa), between intracellular domains RCK1 and RCK2 (4 aa at SS1) and upstream of the calcium "bowl" (27 aa at SS4). Two other truncated variants, X2(92) and X2(188), lacking the intracellular C-terminal (stop downstream of S6), were cloned from cerebral vascular/meningeal tissue. They appear non-functional as no current expression was observed, but the X2(92) appeared to slow the activation of the Zero variant when co-expressed. Positive protein expression of X2(92) was observed in oocytes by immunoblotting and fluorescence using a yellow fluorescent protein-tagged construct. The functional characteristics of the X1 variant may be important for a subpopulation of BK channels in the brain, while the "silent" truncated variants X2(92) and X2(188) may play a role as modulators of other BK channel variants in a way similar to well known beta subunits.
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Affiliation(s)
- Asser Nyander Poulsen
- Department of Animal and Veterinary Basic Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 7, Frederiksberg C, Denmark.
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Chen L, Jeffries O, Rowe ICM, Liang Z, Knaus HG, Ruth P, Shipston MJ. Membrane trafficking of large conductance calcium-activated potassium channels is regulated by alternative splicing of a transplantable, acidic trafficking motif in the RCK1-RCK2 linker. J Biol Chem 2010; 285:23265-75. [PMID: 20479001 PMCID: PMC2906319 DOI: 10.1074/jbc.m110.139758] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2010] [Indexed: 01/26/2023] Open
Abstract
Trafficking of the pore-forming alpha-subunits of large conductance calcium- and voltage-activated potassium (BK) channels to the cell surface represents an important regulatory step in controlling BK channel function. Here, we identify multiple trafficking signals within the intracellular RCK1-RCK2 linker of the cytosolic C terminus of the channel that are required for efficient cell surface expression of the channel. In particular, an acidic cluster-like motif was essential for channel exit from the endoplasmic reticulum and subsequent cell surface expression. This motif could be transplanted onto a heterologous nonchannel protein to enhance cell surface expression by accelerating endoplasmic reticulum export. Importantly, we identified a human alternatively spliced BK channel variant, hSloDelta(579-664), in which these trafficking signals are excluded because of in-frame exon skipping. The hSloDelta(579-664) variant is expressed in multiple human tissues and cannot form functional channels at the cell surface even though it retains the putative RCK domains and downstream trafficking signals. Functionally, the hSloDelta(579-664) variant acts as a dominant negative subunit to suppress cell surface expression of BK channels. Thus alternative splicing of the intracellular RCK1-RCK2 linker plays a critical role in determining cell surface expression of BK channels by controlling the inclusion/exclusion of multiple trafficking motifs.
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Affiliation(s)
- Lie Chen
- From the
Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Owen Jeffries
- From the
Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Iain C. M. Rowe
- From the
Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Zhi Liang
- From the
Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Hans-Guenther Knaus
- the
Division for Molecular and Cellular Pharmacology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Medical University Innsbruck, Peter-Mayr Strasse 1, 6020 Innsbruck, Austria, and
| | - Peter Ruth
- Pharmacology and Toxicology, Institute of Pharmacy, University Tuebingen, 72076 Tuebingen, Germany
| | - Michael J. Shipston
- From the
Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
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Yuan P, Leonetti MD, Pico AR, Hsiung Y, MacKinnon R. Structure of the human BK channel Ca2+-activation apparatus at 3.0 A resolution. Science 2010; 329:182-6. [PMID: 20508092 DOI: 10.1126/science.1190414] [Citation(s) in RCA: 232] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
High-conductance voltage- and Ca2+-activated K+ (BK) channels encode negative feedback regulation of membrane voltage and Ca2+ signaling, playing a central role in numerous physiological processes. We determined the x-ray structure of the human BK Ca2+ gating apparatus at a resolution of 3.0 angstroms and deduced its tetrameric assembly by solving a 6 angstrom resolution structure of a Na+-activated homolog. Two tandem C-terminal regulator of K+ conductance (RCK) domains from each of four channel subunits form a 350-kilodalton gating ring at the intracellular membrane surface. A sequence of aspartic amino acids that is known as the Ca2+ bowl, and is located within the second of the tandem RCK domains, creates four Ca2+ binding sites on the outer perimeter of the gating ring at the "assembly interface" between RCK domains. Functionally important mutations cluster near the Ca2+ bowl, near the "flexible interface" between RCK domains, and on the surface of the gating ring that faces the voltage sensors. The structure suggests that the Ca2+ gating ring, in addition to regulating the pore directly, may also modulate the voltage sensor.
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Affiliation(s)
- Peng Yuan
- Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA
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