1
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Souza DS, Chignalia AZ, Carvalho-de-Souza JL. Modulation of cardiac voltage-activated K + currents by glypican 1 heparan sulfate proteoglycan. Life Sci 2022; 308:120916. [PMID: 36049528 PMCID: PMC11105158 DOI: 10.1016/j.lfs.2022.120916] [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: 05/15/2022] [Revised: 08/15/2022] [Accepted: 08/24/2022] [Indexed: 11/20/2022]
Abstract
BACKGROUND Glypican 1 (Gpc1) is a heparan sulfate proteoglycan attached to the cell membrane via a glycosylphosphatidylinositol anchor, where it holds glycosaminoglycans nearby. We have recently shown that Gpc1 knockout (Gpc1-/-) mice feature decreased systemic blood pressure. To date, none has been reported regarding the role of Gpc1 on the electrical properties of the heart and specifically, in regard to a functional interaction between Gpc1 and voltage-gated K+ channels. METHODS We used echocardiography and in vivo (electrocardiographic recordings) and in vitro (patch clamping) electrophysiology to study mechanical and electric properties of mice hearts. We used RT-PCR to probe K+ channels' gene transcription in heart tissue. RESULTS Gpc1-/- hearts featured increased cardiac stroke volume and preserved ejection fraction. Gpc1-/- electrocardiograms showed longer QT intervals, abnormalities in the ST segment, and delayed T waves, corroborated by longer action potentials in isolated ventricular cardiomyocytes. In voltage-clamp, these cells showed decreased Ito and IK voltage-activated K+ current densities. Moreover, IK showed activation at less negative voltages, but a higher level of inactivation at a given membrane potential. Kcnh2 and Kcnq1 voltage-gated K+ channels subunits' transcripts were remarkably more abundant in heart tissues from Gpc1-/- mice, suggesting that Gpc1 may interfere in the steps between transcription and translation in these cases. CONCLUSION Our data reveals an unprecedented connection between Gpc1 and voltage-gated K+ channels expressed in the heart and this knowledge contributes to the understanding of the role of this HSPG in cardiac function which may play a role in the development of cardiovascular disease.
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Affiliation(s)
- Diego Santos Souza
- Department of Anesthesiology, College of Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Andreia Zago Chignalia
- Department of Anesthesiology, College of Medicine, University of Arizona, Tucson, AZ 85724, USA; Department of Physiology, College of Medicine University of Arizona, Tucson, AZ 85724, USA; Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ 85724, USA
| | - Joao Luis Carvalho-de-Souza
- Department of Anesthesiology, College of Medicine, University of Arizona, Tucson, AZ 85724, USA; Department of Physiology, College of Medicine University of Arizona, Tucson, AZ 85724, USA; Department of Ophthalmology and Visual Sciences, College of Medicine, University of Arizona, Tucson, AZ 85724, USA; BIO5 Institute, University of Arizona, Tucson, AZ 85724, USA.
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2
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Coyote-Maestas W, Nedrud D, He Y, Schmidt D. Determinants of trafficking, conduction, and disease within a K + channel revealed through multiparametric deep mutational scanning. eLife 2022; 11:76903. [PMID: 35639599 PMCID: PMC9273215 DOI: 10.7554/elife.76903] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Accepted: 05/27/2022] [Indexed: 01/04/2023] Open
Abstract
A long-standing goal in protein science and clinical genetics is to develop quantitative models of sequence, structure, and function relationships to understand how mutations cause disease. Deep mutational scanning (DMS) is a promising strategy to map how amino acids contribute to protein structure and function and to advance clinical variant interpretation. Here, we introduce 7429 single-residue missense mutations into the inward rectifier K+ channel Kir2.1 and determine how this affects folding, assembly, and trafficking, as well as regulation by allosteric ligands and ion conduction. Our data provide high-resolution information on a cotranslationally folded biogenic unit, trafficking and quality control signals, and segregated roles of different structural elements in fold stability and function. We show that Kir2.1 surface trafficking mutants are underrepresented in variant effect databases, which has implications for clinical practice. By comparing fitness scores with expert-reviewed variant effects, we can predict the pathogenicity of 'variants of unknown significance' and disease mechanisms of known pathogenic mutations. Our study in Kir2.1 provides a blueprint for how multiparametric DMS can help us understand the mechanistic basis of genetic disorders and the structure-function relationships of proteins.
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Affiliation(s)
- Willow Coyote-Maestas
- Department of Biochemistry, Molecular Biology and Biophysics, University of MinnesotaMinneapolisUnited States
| | - David Nedrud
- Department of Biochemistry, Molecular Biology and Biophysics, University of MinnesotaMinneapolisUnited States
| | - Yungui He
- Department of Genetics, Cell Biology and Development, University of MinnesotaMinneapolisUnited States
| | - Daniel Schmidt
- Department of Genetics, Cell Biology and Development, University of MinnesotaMinneapolisUnited States
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3
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Zhou G, Duong TV, Kasten EP, Hoffmann HM. Low CLOCK and CRY2 in 2nd trimester human maternal blood and risk of preterm birth: A nested case-control study. Biol Reprod 2021; 105:827-836. [PMID: 34142702 DOI: 10.1093/biolre/ioab119] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 05/24/2021] [Accepted: 06/14/2021] [Indexed: 12/18/2022] Open
Abstract
Previous studies have observed an association between maternal circadian rhythm disruption and preterm birth (PTB). However, the underlying molecular mechanisms and the potential of circadian clock genes to serve as predictors of PTB remain unexplored. We examined the association of 10 core circadian transcripts in maternal blood with spontaneous PTB (sPTB) vs term births using a nested case-control study design. We used a public gene expression dataset (GSE59491), which was nested within the All Our Babies (AOB) study cohort in Canada. Maternal blood was sampled in trimesters 2-3 from women with sPTB (n = 51) and term births (n = 106), matched for 5 demographic variables. In 2nd trimester maternal blood, only CLOCK and CRY2 transcripts were significantly lower in sPTB vs term (p = 0.02 ~ 0.03, FDR < 0.20). A change of PER3 mRNA from trimesters 2 to 3 was significantly associated with sPTB (decline in sPTB, p = 0.02, FDR < 0.20). When CLOCK and CRY2 were modeled together in 2nd trimester blood, the odds ratio of being in the low level of both circadian gene transcripts was greater in sPTB vs term (OR = 4.86, 95%CI = (1.75,13.51), p < 0.01). Using GSVA and Pearson correlation, we identified 98 common pathways that were negatively or positively correlated with CLOCK and CRY2 expression (all p < 0.05, FDR < 0.10). The top three identified pathways were amyotrophic lateral sclerosis, degradation of extracellular matrix, and inwardly rectifying potassium channels. These three processes have previously been shown to be involved in neuron death, parturition, and uterine excitability during pregnancy, respectively.
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Affiliation(s)
- Guoli Zhou
- Clinical & Translational Sciences Institute, Michigan State University, USA
| | - Thu V Duong
- Department of Animal Science, The Reproductive and Developmental Sciences Program, College of Agriculture and Natural Resources, Michigan State University, USA
| | - Eric P Kasten
- Clinical & Translational Sciences Institute, Michigan State University, USA.,Department of Radiology, Michigan State University, USA
| | - Hanne M Hoffmann
- Department of Animal Science, The Reproductive and Developmental Sciences Program, College of Agriculture and Natural Resources, Michigan State University, USA
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4
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Schmidt M, Schroeder I, Bauer D, Thiel G, Hamacher K. Inferring functional units in ion channel pores via relative entropy. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2021; 50:37-57. [PMID: 33523249 PMCID: PMC7872957 DOI: 10.1007/s00249-020-01480-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 10/11/2020] [Accepted: 11/09/2020] [Indexed: 11/25/2022]
Abstract
Coarse-grained protein models approximate the first-principle physical potentials. Among those modeling approaches, the relative entropy framework yields promising and physically sound results, in which a mapping from the target protein structure and dynamics to a model is defined and subsequently adjusted by an entropy minimization of the model parameters. Minimization of the relative entropy is equivalent to maximization of the likelihood of reproduction of (configurational ensemble) observations by the model. In this study, we extend the relative entropy minimization procedure beyond parameter fitting by a second optimization level, which identifies the optimal mapping to a (dimension-reduced) topology. We consider anisotropic network models of a diverse set of ion channels and assess our findings by comparison to experimental results.
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Affiliation(s)
- Michael Schmidt
- Department of Physics, TU Darmstadt, Karolinenpl. 5, 64289 Darmstadt, Germany
| | - Indra Schroeder
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Daniel Bauer
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Gerhard Thiel
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Kay Hamacher
- Department of Physics, Department of Biology, Department of Computer Science, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
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5
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Lai X, Xu J, Ma H, Liu Z, Zheng W, Liu J, Zhu H, Zhou Y, Zhou X. Identification and Expression of Inward-Rectifying Potassium Channel Subunits in Plutella xylostella. INSECTS 2020; 11:insects11080461. [PMID: 32707967 PMCID: PMC7469208 DOI: 10.3390/insects11080461] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 07/20/2020] [Accepted: 07/21/2020] [Indexed: 11/30/2022]
Abstract
In insects, inward-rectifying potassium (Kir) channels regulate vital physiological functions, such as feeding behavior, silk secretion, renal excretion, and immune function. Therefore, they offer promising potential as targets for insecticides. Three types of Kir subunits have been identified in Diptera and Hemiptera, but the Kir subunits of Lepidoptera still remain unclear. This study identified five Kir subunit genes (pxkir1, pxkir2, pxkir3A, pxkir3B, and pxkir4) in the transcriptome of Plutella xylostella. Phylogenetic analysis identified pxkir1, pxkir2, pxkir3A, and pxkir3B as orthologous genes of kir1–3 in other insects. Interestingly, pxkir4 may be encoding a new class of Kir subunit in Lepidoptera that has not been reported to date. To identify further Kir channel subunits of P. xylostella, the gene expression profiles of five pxkir genes were studied by quantitative real-time PCR. These pxkir genes are expressed throughout the development of P. xylostella. pxkir1 and pxkir2 were highly expressed in thoraxes and legs, while pxkir3 (3A and 3B) and pxkir4 had high expression levels in the midgut and Malpighian tubules. This study identified the composition and distribution of Kir subunits in P. xylostella for the first time, and provides useful information for the further study of Kir channel subunits in Lepidoptera.
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Affiliation(s)
- Xiaoyi Lai
- Long Ping Branch, Graduate School of Hunan University, Changsha 410125, China; (X.L.); (W.Z.)
| | - Jie Xu
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
| | - Haihao Ma
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
- Correspondence: (H.M.); (X.Z.)
| | - Zheming Liu
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
| | - Wei Zheng
- Long Ping Branch, Graduate School of Hunan University, Changsha 410125, China; (X.L.); (W.Z.)
| | - Jia Liu
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
| | - Hang Zhu
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
| | - Yong Zhou
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
| | - Xiaomao Zhou
- Long Ping Branch, Graduate School of Hunan University, Changsha 410125, China; (X.L.); (W.Z.)
- Institute of Agricultural Biotechnology, Hunan Academy of Agricultural Sciences, Changsha 410125, China; (J.X.); (Z.L.); (J.L.); (H.Z.); (Y.Z.)
- Correspondence: (H.M.); (X.Z.)
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6
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Mackie TD, Brodsky JL. Investigating Potassium Channels in Budding Yeast: A Genetic Sandbox. Genetics 2018; 209:637-650. [PMID: 29967058 PMCID: PMC6028241 DOI: 10.1534/genetics.118.301026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 05/15/2018] [Indexed: 12/26/2022] Open
Abstract
Like all species, the model eukaryote Saccharomyces cerevisiae, or Bakers' yeast, concentrates potassium in the cytosol as an electrogenic osmolyte and enzyme cofactor. Yeast are capable of robust growth on a wide variety of potassium concentrations, ranging from 10 µM to 2.5 M, due to the presence of a high-affinity potassium uptake system and a battery of cation exchange transporters. Genetic perturbation of either of these systems retards yeast growth on low or high potassium, respectively. However, these potassium-sensitized yeast are a powerful genetic tool, which has been leveraged for diverse studies. Notably, the potassium-sensitive cells can be transformed with plasmids encoding potassium channels from bacteria, plants, or mammals, and subsequent changes in growth rate have been found to correlate with the activity of the introduced potassium channel. Discoveries arising from the use of this assay over the past three decades have increased our understanding of the structure-function relationships of various potassium channels, the mechanisms underlying the regulation of potassium channel function and trafficking, and the chemical basis of potassium channel modulation. In this article, we provide an overview of the major genetic tools used to study potassium channels in S. cerevisiae, a survey of seminal studies utilizing these tools, and a prospective for the future use of this elegant genetic approach.
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Affiliation(s)
- Timothy D Mackie
- Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260
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7
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Trezza A, Cicaloni V, Porciatti P, Langella A, Fusi F, Saponara S, Spiga O. From in silico to in vitro: a trip to reveal flavonoid binding on the Rattus norvegicus Kir6.1 ATP-sensitive inward rectifier potassium channel. PeerJ 2018; 6:e4680. [PMID: 29736333 PMCID: PMC5936070 DOI: 10.7717/peerj.4680] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Accepted: 04/09/2018] [Indexed: 12/18/2022] Open
Abstract
Background ATP-sensitive inward rectifier potassium channels (Kir), are a potassium channel family involved in many physiological processes. KATP dysfunctions are observed in several diseases such as hypoglycaemia, hyperinsulinemia, Prinzmetal angina–like symptoms, cardiovascular diseases. Methods A broader view of the KATP mechanism is needed in order to operate on their regulation, and in this work we clarify the structure of the Rattus norvegicus ATP-sensitive inward rectifier potassium channel 8 (Kir6.1), which has been obtained through a homology modelling procedure. Due to the medical use of flavonoids, a considerable increase in studies on their influence on human health has recently been observed, therefore our aim is to study, through computational methods, the three-dimensional (3D) conformation together with mechanism of action of Kir6.1 with three flavonoids. Results Computational analysis by performing molecular dynamics (MD) and docking simulation on rat 3D modelled structure have been completed, in its closed and open conformation state and in complex with Quercetin, 5-Hydroxyflavone and Rutin flavonoids. Our study showed that only Quercetin and 5-Hydroxyflavone were responsible for a significant down-regulation of the Kir6.1 activity, stabilising it in a closed conformation. This hypothesis was supported by in vitro experiments demonstrating that Quercetin and 5-Hydroxyflavone were capable to inhibit KATP currents of rat tail main artery myocytes recorded by the patch-clamp technique. Conclusion Combined methodological approaches, such as molecular modelling, docking and MD simulations of Kir6.1 channel, used to elucidate flavonoids intrinsic mechanism of action, are introduced, revealing a new potential druggable protein site.
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Affiliation(s)
- Alfonso Trezza
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy
| | - Vittoria Cicaloni
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy.,Toscana Life Sciences Foundation, Siena, Italy
| | - Piera Porciatti
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy
| | - Andrea Langella
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy
| | - Fabio Fusi
- Department of Life Sciences, University of Siena, Siena, Italy
| | - Simona Saponara
- Department of Life Sciences, University of Siena, Siena, Italy
| | - Ottavia Spiga
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Siena, Italy
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8
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Cosentino C, Alberio L, Thiel G, Moroni A. Yeast-Based Screening System for the Selection of Functional Light-Driven K + Channels. Methods Mol Biol 2018; 1596:271-285. [PMID: 28293893 DOI: 10.1007/978-1-4939-6940-1_17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/10/2023]
Abstract
Ion channels control the electrical properties of cells by opening and closing (gating) in response to a wide palette of environmental and physiological stimuli. Endowing ion channels with the possibility to be gated by remotely applied stimuli, such as light, provides a tool for in vivo control of cellular functions in behaving animals. We have engineered a synthetic light-gated potassium (K+) channel by connecting an exogenous plant photoreceptor LOV2 domain to the K+ channel pore Kcv. Here, we describe the experimental strategy that we have used to evolve the properties of the channel toward full control of light on pore gating. Our method combines rational and random mutagenesis of the channel followed by a yeast-based screening system for light-activated K+ conductance.
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Affiliation(s)
- Cristian Cosentino
- Department of Biosciences, University of Milan and Biophysics Institute, National Research Council (CNR), Via Celoria 26, 201333, Milan, Italy
| | - Laura Alberio
- Department of Biosciences, University of Milan and Biophysics Institute, National Research Council (CNR), Via Celoria 26, 201333, Milan, Italy
| | - Gerhard Thiel
- Plant Membrane Biophysics, Technical University Darmstadt, Darmstadt, Germany
| | - Anna Moroni
- Department of Biosciences, University of Milan and Biophysics Institute, National Research Council (CNR), Via Celoria 26, 201333, Milan, Italy.
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9
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Mackie TD, Kim BY, Subramanya AR, Bain DJ, O'Donnell AF, Welling PA, Brodsky JL. The endosomal trafficking factors CORVET and ESCRT suppress plasma membrane residence of the renal outer medullary potassium channel (ROMK). J Biol Chem 2018; 293:3201-3217. [PMID: 29311259 DOI: 10.1074/jbc.m117.819086] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 01/02/2018] [Indexed: 11/06/2022] Open
Abstract
Protein trafficking can act as the primary regulatory mechanism for ion channels with high open probabilities, such as the renal outer medullary (ROMK) channel. ROMK, also known as Kir1.1 (KCNJ1), is the major route for potassium secretion into the pro-urine and plays an indispensable role in regulating serum potassium and urinary concentrations. However, the cellular machinery that regulates ROMK trafficking has not been fully defined. To identify regulators of the cell-surface population of ROMK, we expressed a pH-insensitive version of the channel in the budding yeast Saccharomyces cerevisiae We determined that ROMK primarily resides in the endoplasmic reticulum (ER), as it does in mammalian cells, and is subject to ER-associated degradation (ERAD). However, sufficient ROMK levels on the plasma membrane rescued growth on low-potassium medium of yeast cells lacking endogenous potassium channels. Next, we aimed to identify the biological pathways most important for ROMK regulation. Therefore, we used a synthetic genetic array to identify non-essential genes that reduce the plasma membrane pool of ROMK in potassium-sensitive yeast cells. Genes identified in this screen included several members of the endosomal complexes required for transport (ESCRT) and the class-C core vacuole/endosome tethering (CORVET) complexes. Mass spectroscopy analysis confirmed that yeast cells lacking an ESCRT component accumulate higher potassium concentrations. Moreover, silencing of ESCRT and CORVET components increased ROMK levels at the plasma membrane in HEK293 cells. Our results indicate that components of the post-endocytic pathway influence the cell-surface density of ROMK and establish that components in this pathway modulate channel activity.
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Affiliation(s)
| | - Bo-Young Kim
- the Department of Physiology, University of Maryland at Baltimore, Baltimore, Maryland 21201
| | - Arohan R Subramanya
- the Departments of Medicine and Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,the Medicine and Research Services, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, Pennsylvania 15240, and
| | - Daniel J Bain
- Geology and Environmental Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Allyson F O'Donnell
- the Department of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282
| | - Paul A Welling
- the Department of Physiology, University of Maryland at Baltimore, Baltimore, Maryland 21201
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10
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O'Donnell BM, Mackie TD, Subramanya AR, Brodsky JL. Endoplasmic reticulum-associated degradation of the renal potassium channel, ROMK, leads to type II Bartter syndrome. J Biol Chem 2017. [PMID: 28630040 DOI: 10.1074/jbc.m117.786376] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Type II Bartter syndrome is caused by mutations in the renal outer medullary potassium (ROMK) channel, but the molecular mechanisms underlying this disease are poorly defined. To rapidly screen for ROMK function, we developed a yeast expression system and discovered that yeast cells lacking endogenous potassium channels could be rescued by WT ROMK but not by ROMK proteins containing any one of four Bartter mutations. We also found that the mutant proteins were significantly less stable than WT ROMK. However, their degradation was slowed in the presence of a proteasome inhibitor or when yeast cells contained mutations in the CDC48 or SSA1 gene, which is required for endoplasmic reticulum (ER)-associated degradation (ERAD). Consistent with these data, sucrose gradient centrifugation and indirect immunofluorescence microscopy indicated that most ROMK protein was ER-localized. To translate these findings to a more relevant cell type, we measured the stabilities of WT ROMK and the ROMK Bartter mutants in HEK293 cells. As in yeast, the Bartter mutant proteins were less stable than the WT protein, and their degradation was slowed in the presence of a proteasome inhibitor. Finally, we discovered that low-temperature incubation increased the steady-state levels of a Bartter mutant, suggesting that the disease-causing mutation traps the protein in a folding-deficient conformation. These findings indicate that the underlying pathology for at least a subset of patients with type II Bartter syndrome is linked to the ERAD pathway and that future therapeutic strategies should focus on correcting deficiencies in ROMK folding.
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Affiliation(s)
- Brighid M O'Donnell
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260; Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Timothy D Mackie
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Arohan R Subramanya
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260.
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11
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Yenush L. Potassium and Sodium Transport in Yeast. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 892:187-228. [DOI: 10.1007/978-3-319-25304-6_8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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12
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Cioffi AG, Hou J, Grillo AS, Diaz KA, Burke MD. Restored Physiology in Protein-Deficient Yeast by a Small Molecule Channel. J Am Chem Soc 2015; 137:10096-9. [PMID: 26230309 DOI: 10.1021/jacs.5b05765] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Deficiencies of protein ion channels underlie many currently incurable human diseases. Robust networks of pumps and channels are usually responsible for the directional movement of specific ions in organisms ranging from microbes to humans. We thus questioned whether minimally selective small molecule mimics of missing protein channels might be capable of collaborating with the corresponding protein ion pumps to restore physiology. Here we report vigorous and sustainable restoration of yeast cell growth by replacing missing protein ion transporters with imperfect small molecule mimics. We further provide evidence that this tolerance for imperfect mimicry is attributable to collaboration between the channel-forming small molecule and protein ion pumps. These results illuminate a mechanistic framework for pursuing small molecule replacements for deficient protein ion channels that underlie a range of challenging human diseases.
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Affiliation(s)
- Alexander G Cioffi
- †Howard Hughes Medical Institute and ‡Departments of Biochemistry and §Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Jennifer Hou
- †Howard Hughes Medical Institute and ‡Departments of Biochemistry and §Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Anthony S Grillo
- †Howard Hughes Medical Institute and ‡Departments of Biochemistry and §Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Katrina A Diaz
- †Howard Hughes Medical Institute and ‡Departments of Biochemistry and §Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Martin D Burke
- †Howard Hughes Medical Institute and ‡Departments of Biochemistry and §Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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13
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Cosentino C, Alberio L, Gazzarrini S, Aquila M, Romano E, Cermenati S, Zuccolini P, Petersen J, Beltrame M, Van Etten JL, Christie JM, Thiel G, Moroni A. Optogenetics. Engineering of a light-gated potassium channel. Science 2015; 348:707-10. [PMID: 25954011 DOI: 10.1126/science.aaa2787] [Citation(s) in RCA: 109] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 04/07/2015] [Indexed: 12/18/2022]
Abstract
The present palette of opsin-based optogenetic tools lacks a light-gated potassium (K(+)) channel desirable for silencing of excitable cells. Here, we describe the construction of a blue-light-induced K(+) channel 1 (BLINK1) engineered by fusing the plant LOV2-Jα photosensory module to the small viral K(+) channel Kcv. BLINK1 exhibits biophysical features of Kcv, including K(+) selectivity and high single-channel conductance but reversibly photoactivates in blue light. Opening of BLINK1 channels hyperpolarizes the cell to the K(+) equilibrium potential. Ectopic expression of BLINK1 reversibly inhibits the escape response in light-exposed zebrafish larvae. BLINK1 therefore provides a single-component optogenetic tool that can establish prolonged, physiological hyperpolarization of cells at low light intensities.
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Affiliation(s)
| | - Laura Alberio
- Department of Biosciences, University of Milano, Italy
| | | | - Marco Aquila
- Department of Biosciences, University of Milano, Italy
| | | | | | | | - Jan Petersen
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, UK
| | | | - James L Van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, NE 68583-0900, USA
| | - John M Christie
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, UK
| | - Gerhard Thiel
- Membrane Biophysics, Technical University of Darmstadt, Darmstadt, Germany
| | - Anna Moroni
- Department of Biosciences, University of Milano, Italy.
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14
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Fujiwara Y, Kurokawa T, Okamura Y. Long α helices projecting from the membrane as the dimer interface in the voltage-gated H(+) channel. ACTA ACUST UNITED AC 2014; 143:377-86. [PMID: 24567511 PMCID: PMC3933940 DOI: 10.1085/jgp.201311082] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Continuous helices extending from the transmembrane region to the cytoplasmic region form a dimeric interface to regulate activation of the voltage-gated H+ channel. The voltage-gated H+ channel (Hv) is a H+-permeable voltage-sensor domain (VSD) protein that consists of four transmembrane segments (S1–S4). Hv assembles as a dimeric channel and two transmembrane channel domains function cooperatively, which is mediated by the coiled-coil assembly domain in the cytoplasmic C terminus. However, the structural basis of the interdomain interactions remains unknown. Here, we provide a picture of the dimer configuration based on the analyses of interactions among two VSDs and a coiled-coil domain. Systematic mutations of the linker region between S4 of VSD and the coiled-coil showed that the channel gating was altered in the helical periodicity with the linker length, suggesting that two domains are linked by helices. Cross-linking analyses revealed that the two S4 helices were situated closely in the dimeric channel. The interaction interface between the two S4 and the assembly interface of the coiled-coil domain were aligned in the same direction based on the phase angle calculation along α helices. Collectively, we propose that continuous helices stretching from the transmembrane to the cytoplasmic region in the dimeric interface regulate the channel activation in the Hv dimer.
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Affiliation(s)
- Yuichiro Fujiwara
- Integrative Physiology, Graduate School of Medicine, and 2 Graduate School of Frontier Biosciences, Osaka University, Osaka 565-0871, Japan
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15
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Liu BC, Yang LL, Lu XY, Song X, Li XC, Chen G, Li Y, Yao X, Humphrey DR, Eaton DC, Shen BZ, Ma HP. Lovastatin-Induced Phosphatidylinositol-4-Phosphate 5-Kinase Diffusion from Microvilli Stimulates ROMK Channels. J Am Soc Nephrol 2014; 26:1576-87. [PMID: 25349201 DOI: 10.1681/asn.2013121326] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 08/25/2014] [Indexed: 12/13/2022] Open
Abstract
We recently showed that lovastatin attenuates cyclosporin A (CsA)-induced damage of cortical collecting duct (CCD) principal cells by reducing intracellular cholesterol. Previous studies showed that, in cell expression models or artificial membranes, exogenous cholesterol directly inhibits inward rectifier potassium channels, including Kir1.1 (Kcnj1; the gene locus for renal outer medullary K(+) [ROMK1] channels). Therefore, we hypothesized that lovastatin might stimulate ROMK1 by reducing cholesterol in CCD cells. Western blots showed that mpkCCDc14 cells express ROMK1 channels with molecular masses that approximate the molecular masses of ROMK1 in renal tubules detected before and after treatment with DTT. Confocal microscopy showed that ROMK1 channels were not in the microvilli, where cholesterol-rich lipid rafts are located, but rather, the planar regions of the apical membrane of mpkCCDc14 cells. Furthermore, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], an activator of ROMK channels, was detected mainly in the microvilli under resting conditions along with the kinase responsible for PI(4,5)P2 synthesis, phosphatidylinositol-4-phosphate 5-kinase, type I γ [PI(4)P5K I γ], which may explain the low basal open probability and increased sensitivity to tetraethylammonium observed here for this channel. Notably, lovastatin induced PI(4)P5K I γ diffusion into planar regions and elevated PI(4,5)P2 and ROMK1 open probability in these regions through a cholesterol-associated mechanism. However, exogenous cholesterol alone did not induce these effects. These results suggest that lovastatin stimulates ROMK1 channels, at least in part, by inducing PI(4,5)P2 synthesis in planar regions of the renal CCD cell apical membrane, suggesting that lovastatin could reduce cyclosporin-induced nephropathy and associated hyperkalemia.
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Affiliation(s)
- Bing-Chen Liu
- Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | - Li-Li Yang
- Departments of Radiology and Department of Physiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and
| | - Xiao-Yu Lu
- Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | - Xiang Song
- Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | | | | | - Yichao Li
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | - Xincheng Yao
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | | | - Douglas C Eaton
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
| | - Bao-Zhong Shen
- Departments of Radiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and
| | - He-Ping Ma
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
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16
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Bagriantsev SN, Chatelain FC, Clark KA, Alagem N, Reuveny E, Minor DL. Tethered protein display identifies a novel Kir3.2 (GIRK2) regulator from protein scaffold libraries. ACS Chem Neurosci 2014; 5:812-22. [PMID: 25028803 PMCID: PMC4176385 DOI: 10.1021/cn5000698] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
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Use of randomized peptide libraries
to evolve molecules with new
functions provides a means for developing novel regulators of protein
activity. Despite the demonstrated power of such approaches for soluble
targets, application of this strategy to membrane systems, such as
ion channels, remains challenging. Here, we have combined libraries
of a tethered protein scaffold with functional selection in yeast
to develop a novel activator of the G-protein-coupled mammalian inwardly
rectifying potassium channel Kir3.2 (GIRK2). We show that the novel
regulator, denoted N5, increases Kir3.2 (GIRK2) basal activity by
inhibiting clearance of the channel from the cellular surface rather
than affecting the core biophysical properties of the channel. These
studies establish the tethered protein display strategy as a means
to create new channel modulators and highlight the power of approaches
that couple randomized libraries with direct selections for functional
effects. Our results further underscore the possibility for the development
of modulators that influence channel function by altering cell surface
expression densities rather than by direct action on channel biophysical
parameters. The use of tethered library selection strategies coupled
with functional selection bypasses the need for a purified target
and is likely to be applicable to a range of membrane protein systems.
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Affiliation(s)
| | | | | | - Noga Alagem
- Department
of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Eitan Reuveny
- Department
of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Daniel L. Minor
- Physical
Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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17
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Huang TL, Mayence A, Vanden Eynde JJ. Some non-conventional biomolecular targets for diamidines. A short survey. Bioorg Med Chem 2014; 22:1983-92. [DOI: 10.1016/j.bmc.2014.02.049] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 02/19/2014] [Accepted: 02/24/2014] [Indexed: 12/24/2022]
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18
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Kang JY, Kawaguchi D, Coin I, Xiang Z, O'Leary DDM, Slesinger PA, Wang L. In vivo expression of a light-activatable potassium channel using unnatural amino acids. Neuron 2014; 80:358-70. [PMID: 24139041 DOI: 10.1016/j.neuron.2013.08.016] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/09/2013] [Indexed: 01/28/2023]
Abstract
Optical control of protein function provides excellent spatial-temporal resolution for studying proteins in situ. Although light-sensitive exogenous proteins and ligands have been used to manipulate neuronal activity, a method for optical control of neuronal proteins using unnatural amino acids (Uaa) in vivo is lacking. Here, we describe the genetic incorporation of a photoreactive Uaa into the pore of an inwardly rectifying potassium channel Kir2.1. The Uaa occluded the pore, rendering the channel nonconducting, and, on brief light illumination, was released to permit outward K(+) current. Expression of this photoinducible inwardly rectifying potassium (PIRK) channel in rat hippocampal neurons created a light-activatable PIRK switch for suppressing neuronal firing. We also expanded the genetic code of mammals to express PIRK channels in embryonic mouse neocortex in vivo and demonstrated a light-activated PIRK current in cortical neurons. These principles could be generally expanded to other proteins expressed in the brain to enable optical regulation.
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Affiliation(s)
- Ji-Yong Kang
- The Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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19
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Paavilainen S, Guidotti G. Interactions between the transmembrane domains of CD39: identification of interacting residues by yeast selection. SCIENCEOPEN RESEARCH 2014; 2014. [PMID: 26258004 DOI: 10.14293/s2199-1006.1.sorlife.aeeerm.v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Rat CD39, a membrane-bound ectonucleoside triphosphate diphosphohydrolase that hydrolyzes extracellular nucleoside tri- and diphosphates, is anchored to the membrane by two transmembrane domains at the two ends of the molecule. The transmembrane domains are important for enzymatic activity, as mutants lacking one or both of these domains have a fraction of the enzymatic activity of the wild-type CD39. We investigated the interactions between the transmembrane domains by using a strain of yeast that requires surface expression of CD39 for growth. Random mutagenesis of selected amino acid residues in the N-terminal transmembrane domain revealed that the presence of charged amino acids at these positions prevents expression of functional protein. Rescue of the growth of these mutants by complementary mutations on selected residues of the C-terminal transmembrane domain indicates that there is contact between particular faces of the transmembrane domains.
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Affiliation(s)
- Sari Paavilainen
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
| | - Guido Guidotti
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
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20
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Kolb AR, Needham PG, Rothenberg C, Guerriero CJ, Welling PA, Brodsky JL. ESCRT regulates surface expression of the Kir2.1 potassium channel. Mol Biol Cell 2013; 25:276-89. [PMID: 24227888 PMCID: PMC3890348 DOI: 10.1091/mbc.e13-07-0394] [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: 12/16/2022] Open
Abstract
The Kir2.1 potassium channel is targeted by endoplasmic reticulum–associated degradation in yeast. To identify other Kir2.1 quality control factors, a novel yeast screen was performed. ESCRT components were among the strongest hits from the screen. Consistent with these data, ESCRT also regulates Kir2.1 stability in human cells. Protein quality control (PQC) is required to ensure cellular health. PQC is recognized for targeting the destruction of defective polypeptides, whereas regulated protein degradation mechanisms modulate the concentration of specific proteins in concert with physiological demands. For example, ion channel levels are physiologically regulated within tight limits, but a system-wide approach to define which degradative systems are involved is lacking. We focus on the Kir2.1 potassium channel because altered Kir2.1 levels lead to human disease and Kir2.1 restores growth on low-potassium medium in yeast mutated for endogenous potassium channels. Using this system, first we find that Kir2.1 is targeted for endoplasmic reticulum–associated degradation (ERAD). Next a synthetic gene array identifies nonessential genes that negatively regulate Kir2.1. The most prominent gene family that emerges from this effort encodes members of endosomal sorting complex required for transport (ESCRT). ERAD and ESCRT also mediate Kir2.1 degradation in human cells, with ESCRT playing a more prominent role. Thus multiple proteolytic pathways control Kir2.1 levels at the plasma membrane.
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Affiliation(s)
- Alexander R Kolb
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15261 Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
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21
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Zhong M, Kawaguchi R, Ter-Stepanian M, Kassai M, Sun H. Vitamin A transport and the transmembrane pore in the cell-surface receptor for plasma retinol binding protein. PLoS One 2013; 8:e73838. [PMID: 24223695 PMCID: PMC3815300 DOI: 10.1371/journal.pone.0073838] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 07/25/2013] [Indexed: 11/18/2022] Open
Abstract
Vitamin A and its derivatives (retinoids) play diverse and crucial functions from embryogenesis to adulthood and are used as therapeutic agents in human medicine for eye and skin diseases, infections and cancer. Plasma retinol binding protein (RBP) is the principal and specific vitamin A carrier in the blood and binds vitamin A at 1∶1 ratio. STRA6 is the high-affinity membrane receptor for RBP and mediates cellular vitamin A uptake. STRA6 null mice have severely depleted vitamin A reserves for vision and consequently have vision loss, even under vitamin A sufficient conditions. STRA6 null humans have a wide range of severe pathological phenotypes in many organs including the eye, brain, heart and lung. Known membrane transport mechanisms involve transmembrane pores that regulate the transport of the substrate (e.g., the gating of ion channels). STRA6 represents a new type of membrane receptor. How this receptor interacts with its transport substrate vitamin A and the functions of its nine transmembrane domains are still completely unknown. These questions are critical to understanding the molecular basis of STRA6′s activities and its regulation. We employ acute chemical modification to introduce chemical side chains to STRA6 in a site-specific manner. We found that modifications with specific chemicals at specific positions in or near the transmembrane domains of this receptor can almost completely suppress its vitamin A transport activity. These experiments provide the first evidence for the existence of a transmembrane pore, analogous to the pore of ion channels, for this new type of cell-surface receptor.
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Affiliation(s)
- Ming Zhong
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Riki Kawaguchi
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Mariam Ter-Stepanian
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Miki Kassai
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Hui Sun
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- * E-mail:
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22
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Rosenhouse-Dantsker A, Noskov S, Durdagi S, Logothetis DE, Levitan I. Identification of novel cholesterol-binding regions in Kir2 channels. J Biol Chem 2013; 288:31154-64. [PMID: 24019518 DOI: 10.1074/jbc.m113.496117] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inwardly rectifying potassium (Kir) channels play an important role in setting the resting membrane potential and modulating membrane excitability. We have recently shown that cholesterol regulates representative members of the Kir family and that in the majority of the cases, cholesterol suppresses channel function. Furthermore, recent data indicate that cholesterol regulates Kir channels by specific sterol-protein interactions, yet the location of the cholesterol binding site in Kir channels is unknown. Using a combined computational-experimental approach, we show that cholesterol may bind to two nonanular hydrophobic regions in the transmembrane domain of Kir2.1 located between adjacent subunits of the channel. The location of the binding regions suggests that cholesterol modulates channel function by affecting the hinging motion at the center of the pore-lining transmembrane helix that underlies channel gating either directly or through the interface between the N and C termini of the channel.
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Affiliation(s)
- Avia Rosenhouse-Dantsker
- From the Department of Medicine, Pulmonary Section, University of Illinois, Chicago, Illinois 60612
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23
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Bagriantsev SN, Ang KH, Gallardo-Godoy A, Clark KA, Arkin MR, Renslo AR, Minor DL. A high-throughput functional screen identifies small molecule regulators of temperature- and mechano-sensitive K2P channels. ACS Chem Biol 2013; 8:1841-51. [PMID: 23738709 PMCID: PMC3747594 DOI: 10.1021/cb400289x] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
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K2P (KCNK) potassium channels
generate “leak”
potassium currents that strongly influence cellular excitability and
contribute to pain, somatosensation, anesthesia, and mood. Despite
their physiological importance, K2Ps lack specific pharmacology.
Addressing this issue has been complicated by the challenges that
the leak nature of K2P currents poses for electrophysiology-based
high-throughput screening strategies. Here, we present a yeast-based
high-throughput screening assay that avoids this problem. Using a
simple growth-based functional readout, we screened a library of 106,281
small molecules and identified two new inhibitors and three new activators
of the mammalian K2P channel K2P2.1 (KCNK2, TREK-1). By combining biophysical, structure–activity,
and mechanistic analysis, we developed a dihydroacridine analogue,
ML67-33, that acts as a low micromolar, selective activator of temperature-
and mechano-sensitive K2P channels. Biophysical studies
show that ML67-33 reversibly increases channel currents by activating
the extracellular selectivity filter-based C-type gate that forms
the core gating apparatus on which a variety of diverse modulatory
inputs converge. The new K2P modulators presented here,
together with the yeast-based assay, should enable both mechanistic
and physiological studies of K2P activity and facilitate
the discovery and development of other K2P small molecule
modulators.
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Affiliation(s)
| | | | | | | | | | | | - Daniel L. Minor
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California
94720, United States
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24
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Using yeast to study potassium channel function and interactions with small molecules. Methods Mol Biol 2013; 995:31-42. [PMID: 23494370 DOI: 10.1007/978-1-62703-345-9_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Analysis of ion channel mutants is a widely used approach for dissecting ion channel function and for characterizing the mechanisms of action of channel-directed modulators. Expression of functional potassium channels in potassium-uptake-deficient yeast together with genetic selection approaches offers an unbiased, high-throughput, activity-based readout that can rapidly identify large numbers of active ion channel mutants. Because of the assumption-free nature of the method, detailed biophysical analysis of the functional mutants from such selections can provide new and unexpected insights into both ion channel gating and ion channel modulator mechanisms. Here, we present detailed protocols for generation and identification of functional mutations in potassium channels using yeast selections in the potassium-uptake-deficient strain SGY1528. This approach is applicable for the analysis of structure-function relationships of potassium channels from a wide range of sources including viruses, bacteria, plants, and mammals and can be used as a facile way to probe the interactions between ion channels and small-molecule modulators.
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25
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Greiner T, Ramos J, Alvarez MC, Gurnon JR, Kang M, Van Etten JL, Moroni A, Thiel G. Functional HAK/KUP/KT-like potassium transporter encoded by chlorella viruses. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2011; 68:977-986. [PMID: 21848655 DOI: 10.1111/j.1365-313x.2011.04748.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Chlorella viruses are a source of interesting membrane transport proteins. Here we examine a putative K(+) transporter encoded by virus FR483 and related chlorella viruses. The protein shares sequence and structural features with HAK/KUP/KT-like K(+) transporters from plants, bacteria and fungi. Yeast complementation assays and Rb(+) uptake experiments show that the viral protein, termed HAKCV (high-affinity K(+) transporter of chlorella virus), is functional, with transport characteristics that are similar to those of known K(+) transporters. Expression studies revealed that the protein is expressed as an early gene during viral replication, and proteomics data indicate that it is not packaged in the virion. The function of HAKCV is unclear, but the data refute the hypothesis that the transporter acts as a substitute for viral-encoded K(+) channels during virus infection.
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Affiliation(s)
- Timo Greiner
- Institute of Botany at the Technische Universität Darmstadt, Schnittspahnstrasse 3-5, 64287 Darmstadt, Germany
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26
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Multiple modalities converge on a common gate to control K2P channel function. EMBO J 2011; 30:3594-606. [PMID: 21765396 PMCID: PMC3181481 DOI: 10.1038/emboj.2011.230] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Accepted: 06/17/2011] [Indexed: 01/19/2023] Open
Abstract
K2P potassium channels play important roles in the regulation of neuronal excitability. K2P channels are gated chemical, thermal, and mechanical stimuli, and the present study identifies and characterizes a common molecular gate that responds to all different stimuli, both activating and inhibitory ones. Members of the K2P potassium channel family regulate neuronal excitability and are implicated in pain, anaesthetic responses, thermosensation, neuroprotection, and mood. Unlike other potassium channels, K2Ps are gated by remarkably diverse stimuli that include chemical, thermal, and mechanical modalities. It has remained unclear whether the various gating inputs act through separate or common channel elements. Here, we show that protons, heat, and pressure affect activity of the prototypical, polymodal K2P, K2P2.1 (KCNK2/TREK-1), at a common molecular gate that comprises elements of the pore-forming segments and the N-terminal end of the M4 transmembrane segment. We further demonstrate that the M4 gating element is conserved among K2Ps and is employed regardless of whether the gating stimuli are inhibitory or activating. Our results define a unique gating mechanism shared by K2P family members and suggest that their diverse sensory properties are achieved by coupling different molecular sensors to a conserved core gating apparatus.
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27
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Kolb AR, Buck TM, Brodsky JL. Saccharomyces cerivisiae as a model system for kidney disease: what can yeast tell us about renal function? Am J Physiol Renal Physiol 2011; 301:F1-11. [PMID: 21490136 PMCID: PMC3129885 DOI: 10.1152/ajprenal.00141.2011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Accepted: 04/11/2011] [Indexed: 01/18/2023] Open
Abstract
Ion channels, solute transporters, aquaporins, and factors required for signal transduction are vital for kidney function. Because mutations in these proteins or in associated regulatory factors can lead to disease, an investigation into their biogenesis, activities, and interplay with other proteins is essential. To this end, the yeast, Saccharomyces cerevisiae, represents a powerful experimental system. Proteins expressed in yeast include the following: 1) ion channels, including the epithelial sodium channel, members of the inward rectifying potassium channel family, and cystic fibrosis transmembrane conductance regulator; 2) plasma membrane transporters, such as the Na(+)-K(+)-ATPase, the Na(+)-phosphate cotransporter, and the Na(+)-H(+) ATPase; 3) aquaporins 1-4; and 4) proteins such as serum/glucocorticoid-induced kinase 1, phosphoinositide-dependent kinase 1, Rh glycoprotein kidney, and trehalase. The variety of proteins expressed and studied emphasizes the versatility of yeast, and, because of the many available tools in this organism, results can be obtained rapidly and economically. In most cases, data gathered using yeast have been substantiated in higher cell types. These attributes validate yeast as a model system to explore renal physiology and suggest that research initiated using this system may lead to novel therapeutics.
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Affiliation(s)
- Alexander R Kolb
- University of Pittsburgh, 4249 Fifth Ave., A320 Langley Hall, Pittsburgh, PA 15260, USA
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28
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Gebhardt M, Hoffgaard F, Hamacher K, Kast SM, Moroni A, Thiel G. Membrane anchoring and interaction between transmembrane domains are crucial for K+ channel function. J Biol Chem 2011; 286:11299-306. [PMID: 21310959 PMCID: PMC3064186 DOI: 10.1074/jbc.m110.211672] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2010] [Revised: 01/27/2011] [Indexed: 11/06/2022] Open
Abstract
The small viral channel Kcv is a Kir-like K(+) channel of only 94 amino acids. With this simple structure, the tetramer of Kcv represents the pore module of all complex K(+) channels. To examine the structural contribution of the transmembrane domains (TMDs) to channel function, we performed Ala scanning mutagenesis of the two domains and tested the functionality of the mutants in a yeast complementation assay. The data reveal, in combination with computational models, that the upper halves of both TMDs, which face toward the external medium, are rather rigid, whereas the inner parts are more flexible. The rigidity of the outer TMD is conferred by a number of essential aromatic amino acids that face the membrane and probably anchor this domain in the bilayer. The inner TMD is intimately connected with the rigid part of the outer TMD via π···π interactions between a pair of aromatic amino acids. This structural principle is conserved within the viral K(+) channels and also present in Kir2.2, implying a general importance of this architecture for K(+) channel function.
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Affiliation(s)
| | - Franziska Hoffgaard
- the Computational Biology Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Kay Hamacher
- the Computational Biology Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Stefan M. Kast
- the Physikalische Chemie III, Technische Universität Dortmund, 44227 Dortmund, Germany, and
| | - Anna Moroni
- the Department of Biology and Consiglio Nazionale delle Ricerche Istituto di Biofisica-Milano, Università degli Studi di Milano, 20122 Milan, Italy
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29
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Koprowski P, Grajkowski W, Isacoff EY, Kubalski A. Genetic screen for potassium leaky small mechanosensitive channels (MscS) in Escherichia coli: recognition of cytoplasmic β domain as a new gating element. J Biol Chem 2011; 286:877-88. [PMID: 20978126 PMCID: PMC3013047 DOI: 10.1074/jbc.m110.176131] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Revised: 10/07/2010] [Indexed: 01/05/2023] Open
Abstract
Mechanosensitive membrane channels in bacteria respond to the mechanical stretching of the membrane. They will open when bacteria are subjected to rapid osmotic down shock. MscS is a bacterial mechanosensitive channel of small conductance. It is a heptameric membrane protein whose transmembrane part, including the gate and its kinetics, has been well characterized. MscS has a large cytoplasmic domain of a cage-like shape that changes its conformation upon gating, but its involvement in gating is not understood. We screened MscS for mutations that cause potassium leak in Escherichia coli strains deficient in potassium transport systems. We did a phenotypic analysis of single and multiple mutants and recorded the single channel activities of some of them. After these analyses, we attributed the effects of a number of mutations to particular functional states of the channel. Our screen revealed that MscS leaks potassium in a desensitized and in an inactivated state. It also appeared that the lower part of TM3 (transmembrane, pore-forming helix) and the cytoplasmic β domain are tightly packed in the inactivated state but are dissociated in the open state. We attribute the TM3-β interaction to stabilization of the inactivated state in MscS and to the control of tight closure of its membrane pore.
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Affiliation(s)
- Piotr Koprowski
- From the Department of Cell Biology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland and
| | - Wojciech Grajkowski
- From the Department of Cell Biology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland and
| | - Ehud Y. Isacoff
- the Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200
| | - Andrzej Kubalski
- From the Department of Cell Biology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland and
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30
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Paynter JJ, Andres-Enguix I, Fowler PW, Tottey S, Cheng W, Enkvetchakul D, Bavro VN, Kusakabe Y, Sansom MSP, Robinson NJ, Nichols CG, Tucker SJ. Functional complementation and genetic deletion studies of KirBac channels: activatory mutations highlight gating-sensitive domains. J Biol Chem 2010; 285:40754-61. [PMID: 20876570 PMCID: PMC3003375 DOI: 10.1074/jbc.m110.175687] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 09/27/2010] [Indexed: 12/16/2022] Open
Abstract
The superfamily of prokaryotic inwardly rectifying (KirBac) potassium channels is homologous to mammalian Kir channels. However, relatively little is known about their regulation or about their physiological role in vivo. In this study, we have used random mutagenesis and genetic complementation in K(+)-auxotrophic Escherichia coli and Saccharomyces cerevisiae to identify activatory mutations in a range of different KirBac channels. We also show that the KirBac6.1 gene (slr5078) is necessary for normal growth of the cyanobacterium Synechocystis PCC6803. Functional analysis and molecular dynamics simulations of selected activatory mutations identified regions within the slide helix, transmembrane helices, and C terminus that function as important regulators of KirBac channel activity, as well as a region close to the selectivity filter of KirBac3.1 that may have an effect on gating. In particular, the mutations identified in TM2 favor a model of KirBac channel gating in which opening of the pore at the helix-bundle crossing plays a far more important role than has recently been proposed.
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Affiliation(s)
| | | | - Philip W. Fowler
- the Structural Bioinformatics and Computational Biochemistry Unit, Department of Biochemistry
| | - Stephen Tottey
- the Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle NE1 7RU, United Kingdom
| | - Wayland Cheng
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Decha Enkvetchakul
- the Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104, and
| | | | | | - Mark S. P. Sansom
- the Structural Bioinformatics and Computational Biochemistry Unit, Department of Biochemistry
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Nigel J. Robinson
- the Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle NE1 7RU, United Kingdom
| | - Colin G. Nichols
- the Department of Cell Biology and Physiology, and Center for Investigation of Membrane Excitability Disorders, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Stephen J. Tucker
- the Department of Physics, Clarendon Laboratory, and
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
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31
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Paynter JJ, Shang L, Bollepalli MK, Baukrowitz T, Tucker SJ. Random mutagenesis screening indicates the absence of a separate H(+)-sensor in the pH-sensitive Kir channels. Channels (Austin) 2010; 4:390-7. [PMID: 20699659 DOI: 10.4161/chan.4.5.13006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Several inwardly-rectifying (Kir) potassium channels (Kir1.1, Kir4.1 and Kir4.2) are characterised by their sensitivity to inhibition by intracellular H(+) within the physiological range. The mechanism by which these channels are regulated by intracellular pH has been the subject of intense scrutiny for over a decade, yet the molecular identity of the titratable pH-sensor remains elusive. In this study we have taken advantage of the acidic intracellular environment of S. cerevisiae and used a K(+) -auxotrophic strain to screen for mutants of Kir1.1 with impaired pH-sensitivity. In addition to the previously identified K80M mutation, this unbiased screening approach identified a novel mutation (S172T) in the second transmembrane domain (TM2) that also produces a marked reduction in pH-sensitivity through destabilization of the closed-state. However, despite this extensive mutagenic approach, no mutations could be identified which removed channel pH-sensitivity or which were likely to act as a separate H(+) -sensor unique to the pH-sensitive Kir channels. In order to explain these results we propose a model in which the pH-sensing mechanism is part of an intrinsic gating mechanism common to all Kir channels, not just the pH-sensitive Kir channels. In this model, mutations which disrupt this pH-sensor would result in an increase, not reduction, in pH-sensitivity. This has major implications for any future studies of Kir channel pH-sensitivity and explains why formal identification of these pH-sensing residues still represents a major challenge.
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Affiliation(s)
- Jennifer J Paynter
- Department of Physiology, Anatomy and Genetics, University of Oxford, UK
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32
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Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y. Inwardly rectifying potassium channels: their structure, function, and physiological roles. Physiol Rev 2010; 90:291-366. [PMID: 20086079 DOI: 10.1152/physrev.00021.2009] [Citation(s) in RCA: 1074] [Impact Index Per Article: 76.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.
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Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Graduate School of Medicine and The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka 565-0871, Japan
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33
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Chatelain FC, Gazzarrini S, Fujiwara Y, Arrigoni C, Domigan C, Ferrara G, Pantoja C, Thiel G, Moroni A, Minor DL. Selection of inhibitor-resistant viral potassium channels identifies a selectivity filter site that affects barium and amantadine block. PLoS One 2009; 4:e7496. [PMID: 19834614 PMCID: PMC2759520 DOI: 10.1371/journal.pone.0007496] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Accepted: 09/23/2009] [Indexed: 12/02/2022] Open
Abstract
Background Understanding the interactions between ion channels and blockers remains an important goal that has implications for delineating the basic mechanisms of ion channel function and for the discovery and development of ion channel directed drugs. Methodology/Principal Findings We used genetic selection methods to probe the interaction of two ion channel blockers, barium and amantadine, with the miniature viral potassium channel Kcv. Selection for Kcv mutants that were resistant to either blocker identified a mutant bearing multiple changes that was resistant to both. Implementation of a PCR shuffling and backcrossing procedure uncovered that the blocker resistance could be attributed to a single change, T63S, at a position that is likely to form the binding site for the inner ion in the selectivity filter (site 4). A combination of electrophysiological and biochemical assays revealed a distinct difference in the ability of the mutant channel to interact with the blockers. Studies of the analogous mutation in the mammalian inward rectifier Kir2.1 show that the T→S mutation affects barium block as well as the stability of the conductive state. Comparison of the effects of similar barium resistant mutations in Kcv and Kir2.1 shows that neighboring amino acids in the Kcv selectivity filter affect blocker binding. Conclusions/Significance The data support the idea that permeant ions have an integral role in stabilizing potassium channel structure, suggest that both barium and amantadine act at a similar site, and demonstrate how genetic selections can be used to map blocker binding sites and reveal mechanistic features.
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Affiliation(s)
- Franck C. Chatelain
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Sabrina Gazzarrini
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Yuichiro Fujiwara
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Cristina Arrigoni
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Courtney Domigan
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Giuseppina Ferrara
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Carlos Pantoja
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
| | - Gerhard Thiel
- Technische Universität Darmstadt, Institute für Botanik, Darmstadt, Germany
| | - Anna Moroni
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Daniel L. Minor
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
- Department of California Institute for Quantitative Biomedical Research, University of California San Francisco, San Francisco, California, United States of America
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America
- * E-mail:
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34
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Choe S, Grabe M. Conformational dynamics of the inner pore helix of voltage-gated potassium channels. J Chem Phys 2009; 130:215103. [PMID: 19508102 DOI: 10.1063/1.3138906] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Voltage-gated potassium (Kv) channels control the electrical excitability of neurons and muscles. Despite this key role, how these channels open and close or gate is not fully understood. Gating is usually attributed to the bending and straightening of pore-lining helices at glycine and proline residues. In this work we focused on the role of proline in the Pro-Val-Pro (PVP) motif of the inner S6 helix in the Kv1.2 channel. We started by developing a simple hinged-rod model to fully explore the configurational space of bent helices and we related these configurations to the degree of pore opening. We then carried out fully atomistic simulations of the S6 helices and compared these simulations to the hinged-rod model. Both methods suggest that Kv1 channels are not tightly closed when the inner helices are straight, unlike what is seen in the non-PVP containing channels KcsA and KirBac. These results invite the possibility that the S6 helices may be kinked when Kv1 channels are closed. Our simulations indicate that the wild-type helix adopts multiple spatially distinct configurations, which is consistent with its role in adopting a closed state and an open state. The two most dominant configurational basins correspond to a 6 A movement of the helix tail accompanied by the PVP region undergoing a local alpha-helix to 3(10)-helix transition. We explored how single point mutations affect the propensity of the S6 helix to adopt particular configurations. Interestingly, mutating the first proline, P405 (P473 in Shaker), to alanine completely removed the bistable nature of the S6 helix possibly explaining why this mutation compromises the channel. Next, we considered four other mutations in the area known to affect channel gating and we saw similarly dramatic changes to the helix's dynamics and range of motion. Our results suggest a possible mechanism of helix pore closure and they suggest differences in the closed state of glycine-only channels, like KcsA, and PVP containing channels.
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Affiliation(s)
- Seungho Choe
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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35
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Minor DL. Searching for interesting channels: pairing selection and molecular evolution methods to study ion channel structure and function. MOLECULAR BIOSYSTEMS 2009; 5:802-10. [PMID: 19603113 DOI: 10.1039/b901708a] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The pairing of selection and screening methods with randomly mutated libraries can be an exceptionally powerful means for probing the functions of biological molecules and for developing novel regents from random libraries of peptides and oligonucleotides. The use of such approaches is beginning to permeate the ion channel field where they are being deployed to uncover fundamental aspects about ion channel structure and gating, small molecule-channel interactions, and the development of novel agents to control channel activity.
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Affiliation(s)
- Daniel L Minor
- Department of Biochemistry and Biophysics, Cardiovascular Research Institute, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158-2330, USA.
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36
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Gazzarrini S, Kang M, Abenavoli A, Romani G, Olivari C, Gaslini D, Ferrara G, van Etten JL, Kreim M, Kast SM, Thiel G, Moroni A. Chlorella virus ATCV-1 encodes a functional potassium channel of 82 amino acids. Biochem J 2009; 420:295-303. [PMID: 19267691 PMCID: PMC2903877 DOI: 10.1042/bj20090095] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chlorella virus PBCV-1 (Paramecium bursaria chlorella virus-1) encodes the smallest protein (94 amino acids, named Kcv) previously known to form a functional K+ channel in heterologous systems. In this paper, we characterize another chlorella virus encoded K+ channel protein (82 amino acids, named ATCV-1 Kcv) that forms a functional channel in Xenopus oocytes and rescues Saccharomyces cerevisiae mutants that lack endogenous K+ uptake systems. Compared with the larger PBCV-1 Kcv, ATCV-1 Kcv lacks a cytoplasmic N-terminus and has a reduced number of charged amino acids in its turret domain. Despite these deficiencies, ATCV-1 Kcv accomplishes all the major features of K+ channels: it assembles into a tetramer, is K+ selective and is inhibited by the canonical K+ channel blockers, barium and caesium. Single channel analyses reveal a stochastic gating behaviour and a voltage-dependent conductance that resembles the macroscopic I/V relationship. One difference between PBCV-1 and ATCV-1 Kcv is that the latter is more permeable to K+ than Rb+. This difference is partially explained by the presence of a tyrosine residue in the selective filter of ATCV-1 Kcv, whereas PBCV-1 Kcv has a phenylalanine. Hence, ATCV-1 Kcv is the smallest protein to form a K+ channel and it will serve as a model for studying structure-function correlations inside the potassium channel pore.
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Affiliation(s)
- Sabrina Gazzarrini
- Department of Biology and CNR - Istituto di Biofisica, Università degli Studi di Milano, Italy
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37
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Wang WH, Giebisch G. Regulation of potassium (K) handling in the renal collecting duct. Pflugers Arch 2009; 458:157-68. [PMID: 18839206 PMCID: PMC2730119 DOI: 10.1007/s00424-008-0593-3] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/20/2008] [Indexed: 12/13/2022]
Abstract
This review provides an overview of the molecular mechanisms of K transport in the mammalian connecting tubule (CNT) and cortical collecting duct (CCD), both nephron segments responsible for the regulation of renal K secretion. Aldosterone and dietary K intake are two of the most important factors regulating K secretion in the CNT and CCD. Recently, angiotensin II (AngII) has also been shown to play a role in the regulation of K secretion. In addition, genetic and molecular biological approaches have further identified new mechanisms by which aldosterone and dietary K intake regulate K transport. Thus, the interaction between serum-glucocorticoid-induced kinase 1 (SGK1) and with-no-lysine kinase 4 (WNK4) plays a significant role in mediating the effect of aldosterone on ROMK (Kir1.1), an important apical K channel modulating K secretion. Recent evidence suggests that WNK1, mitogen-activated protein kinases such as P38, ERK, and Src family protein tyrosine kinase are involved in mediating the effect of low K intake on apical K secretory channels.
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Affiliation(s)
- Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, 10595, USA.
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38
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Identification of a C-terminus domain critical for the sensitivity of Kir2.1 to cholesterol. Proc Natl Acad Sci U S A 2009; 106:8055-60. [PMID: 19416905 DOI: 10.1073/pnas.0809847106] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A variety of ion channels are regulated by cholesterol, a major lipid component of the plasma membrane whose excess is associated with multiple pathological conditions. However, the mechanism underlying cholesterol sensitivity of ion channels is unknown. We have recently shown that an increase in membrane cholesterol suppresses inwardly rectifying K(+) (Kir2) channels that are responsible for maintaining membrane potential in a variety of cell types. Here we show that cholesterol sensitivity of Kir2 channels depends on a specific region of the C terminus of the cytosolic domain of the channel, the CD loop. Within this loop, the L222I mutation in Kir2.1 abrogates the sensitivity of the channel to cholesterol whereas a reverse mutation in the corresponding position in Kir2.3, I214L, has the opposite effect, increasing cholesterol sensitivity. Furthermore, the L222I mutation has a dominant negative effect on cholesterol sensitivity of Kir2.1 WT. Mutations of 2 additional residues in the CD loop in Kir2.1, N216D and K219Q, partially affect the sensitivity of the channel to cholesterol. Yet, whereas these mutations have been shown to affect activation of the channel by the membrane phospholipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)], other mutations outside the CD loop that have been previously shown to affect activation of the channel by PI(4,5)P(2) had no effect on cholesterol sensitivity. Mutations of the lipid-facing residues of the outer transmembrane helix also had no effect. These findings provide insights into the structural determinants of the sensitivity of Kir2 channels to cholesterol, and introduce the critical role of the cytosolic domain in cholesterol dependent channel regulation.
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Abstract
K(+) channels are revered for their universal action of suppressing electrical activity in nerve and muscle, as well as regulating salt and water transport in epithelial tissues involved in metabolism and digestion. These multisubunit membrane-embedded proteins carry out their physiological chore, selectively allowing the passage of potassium across the membrane, in response to changes in membrane voltage and ligand concentration. Elucidating the diverse gating properties of K(+) channels is of great biological interest since their molecular motions provide insight into how these structurally similar proteins function in a wide variety of tissues. Armed with patch clamps, chart recorders, and now high-resolution structures, electrophysiologists have been dipping into the top tray of the chemist's tool box: synthesizing cysteine-modifying agents and organic cations and grinding up insects, spiders, and other vermin to isolate natural products to poke, probe, and prod K(+) channels. Recently, there has been further cross-fertilization between chemists and K(+) channelologists, resulting in greater accessibility to more elaborate synthetic methodologies and screening approaches. In this review, we catalogue the evolution of chemical tools and approaches that have been utilized to elucidate the mechanistic underpinnings of K(+) channel biology.
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Affiliation(s)
- Christopher A Ahern
- Department of Anesthesiology, University of British Columbia, 2350 Health Science Mall, Vancouver, BC V6T 1Z3, Canada.
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40
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Lee YM, Thompson GA, Ashmole I, Leyland M, So I, Stanfield PR. Multiple residues in the p-region and m2 of murine kir 2.1 regulate blockage by external ba. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2009; 13:61-70. [PMID: 19885028 PMCID: PMC2766715 DOI: 10.4196/kjpp.2009.13.1.61] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
We have examined the effects of certain mutations of the selectivity filter and of the membrane helix M2 on Ba(2+) blockage of the inward rectifier potassium channel, Kir 2.1. We expressed mutant and wild type murine Kir 2.1 in Chinese hamster ovary (CHO) cells and used the whole cell patch-clamp technique to record K(+) currents in the absence and presence of externally applied Ba(2+). Wild type Kir2.1 was blocked by externally applied Ba(2+) in a voltage and concentration dependent manner. Mutants of Y145 in the selectivity filter showed little change in the kinetics of Ba(2+) blockage. The estimated K(d)(0) was 108 microM for Kir2.1 wild type, 124 microM for a concatameric WT-Y145V dimer, 109 microM for a WT-Y145L dimer, and 267 microM for Y145F. Mutant channels T141A and S165L exhibit a reduced affinity together with a large reduction in the rate of blockage. In S165L, blockage proceeds with a double exponential time course, suggestive of more than one blocking site. The double mutation T141A/S165L dramatically reduced affinity for Ba(2+), also showing two components with very different time courses. Mutants D172K and D172R (lining the central, aqueous cavity of the channel) showed both a decreased affinity to Ba(2+) and a decrease in the on transition rate constant (k(on)). These results imply that residues stabilising the cytoplasmic end of the selectivity filter (T141, S165) and in the central cavity (D172) are major determinants of high affinity Ba(2+) blockage in Kir 2.1.
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Affiliation(s)
- Young Mee Lee
- Department of Physiology and Biophysics, Seoul National University, College of Medicine, Seoul 110-799, Korea
| | - Gareth A. Thompson
- Department of Cell Physiology & Pharmacology, University of Leicester, PO Box 138, Leicester, LE1 9HN, UK
| | - Ian Ashmole
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL; Ion Channel Group, UK
| | - Mark Leyland
- Department of Biochemistry, University of L:eicester, LE1 7RH, UK
| | - Insuk So
- Department of Physiology and Biophysics, Seoul National University, College of Medicine, Seoul 110-799, Korea
| | - Peter R. Stanfield
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL; Ion Channel Group, UK
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41
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Paynter JJ, Sarkies P, Andres-Enguix I, Tucker SJ. Genetic selection of activatory mutations in KcsA. Channels (Austin) 2008; 2:413-8. [PMID: 18797191 DOI: 10.4161/chan.2.6.6874] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The KcsA potassium channel from Streptomyces lividans is one of the most actively studied ion channels. However, there are still unresolved issues about its gating mechanism in vivo because the channel is only activated by highly acidic intracellular pH, meaning that it will be mostly inactive in its host environment. In this study we have used a genetic complementation assay of K+-auxotrophic E. coli (TK2420) and S. cerevisiae (SGY1528) to identify activatory or 'gain-of-function' mutations which allow functional activity of KcsA in the physiological environment of two markedly different expression systems. These mutations clustered at the helix-bundle-crossing in both TM1 and TM2 (residues H25, L105, A108, T112, W113, F114, E118 and Q119), and include residues previously implicated in the pH-gating mechanism. We discuss how these gain-of-function mutations may result in their activatory phenotype, the relative merits of the E. coli and S. cerevisiae genetic complementation approaches for the identification of gating mutations in prokaryotic K+ channels, and ways in which this assay may be improved for future use in screening protocols.
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Affiliation(s)
- Jennifer J Paynter
- Oxford Centre for Gene Function, Department of Physiology Anatomy and Genetics, University of Oxford, Oxford, UK
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42
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Robertson JL, Palmer LG, Roux B. Long-pore electrostatics in inward-rectifier potassium channels. ACTA ACUST UNITED AC 2008; 132:613-32. [PMID: 19001143 PMCID: PMC2585864 DOI: 10.1085/jgp.200810068] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Inward-rectifier potassium (Kir) channels differ from the canonical K+ channel structure in that they possess a long extended pore (∼85 Å) for ion conduction that reaches deeply into the cytoplasm. This unique structural feature is presumably involved in regulating functional properties specific to Kir channels, such as conductance, rectification block, and ligand-dependent gating. To elucidate the underpinnings of these functional roles, we examine the electrostatics of an ion along this extended pore. Homology models are constructed based on the open-state model of KirBac1.1 for four mammalian Kir channels: Kir1.1/ROMK, Kir2.1/IRK, Kir3.1/GIRK, and Kir6.2/KATP. By solving the Poisson-Boltzmann equation, the electrostatic free energy of a K+ ion is determined along each pore, revealing that mammalian Kir channels provide a favorable environment for cations and suggesting the existence of high-density regions in the cytoplasmic domain and cavity. The contribution from the reaction field (the self-energy arising from the dielectric polarization induced by the ion's charge in the complex geometry of the pore) is unfavorable inside the long pore. However, this is well compensated by the electrostatic interaction with the static field arising from the protein charges and shielded by the dielectric surrounding. Decomposition of the static field provides a list of residues that display remarkable correspondence with existing mutagenesis data identifying amino acids that affect conduction and rectification. Many of these residues demonstrate interactions with the ion over long distances, up to 40 Å, suggesting that mutations potentially affect ion or blocker energetics over the entire pore. These results provide a foundation for understanding ion interactions in Kir channels and extend to the study of ion permeation, block, and gating in long, cation-specific pores.
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Affiliation(s)
- Janice L Robertson
- Program in Physiology, Biophysics and Systems Biology, Weill Graduate School of Medical Sciences, Cornell University, New York, NY 10065, USA
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Toloue MM, Woolwine Y, Karcz JA, Kasperek EM, Nicholson BJ, Skerrett IM. Site-directed mutagenesis reveals putative regions of protein interaction within the transmembrane domains of connexins. ACTA ACUST UNITED AC 2008; 15:95-105. [PMID: 18649182 DOI: 10.1080/15419060802013463] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Through cysteine-scanning mutagenesis, the authors have compared sites within the transmembrane domains of two connexins, one from the alpha-class (Cx50) and one from the beta-class (Cx32), where amino acid substitution disrupts the function of gap junction channels. In Cx32, 11 sites resulted in no channel function, or an aberrant voltage gating phenotype referred to as "reverse gating," whereas in Cx50, 7 such sites were identified. In both connexins, the sites lie along specific faces of transmembrane helices, suggesting that these may be sites of transmembrane domain interactions. In Cx32, one broad face of the M1 transmembrane domain and a narrower, polar face of M3 were identified, including one site that was shown to come into close apposition with M4 in the closed state. In Cx50, the same face of M3 was identified, but sensitive sites in M1 differed from Cx32. Many fewer sites in M1 disrupted channel function in Cx50, and those that did were on a different helical face to the sensitive sites in Cx32. A more in depth study of two sites in M1 and M2 of Cx32 showed that side-chain length or branching are important for maintenance of normal channel behavior, consistent with this being a site of transmembrane domain interaction.
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Affiliation(s)
- M M Toloue
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA
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44
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Transmembrane domain length of viral K+ channels is a signal for mitochondria targeting. Proc Natl Acad Sci U S A 2008; 105:12313-8. [PMID: 18719119 DOI: 10.1073/pnas.0805709105] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
K(+) channels operate in the plasma membrane and in membranes of organelles including mitochondria. The mechanisms and topogenic information for their differential synthesis and targeting is unknown. This article describes 2 similar viral K(+) channels that are differentially sorted; one protein (Kesv) is imported by the Tom complex into the mitochondria, the other (Kcv) to the plasma membrane. By creating chimeras we discovered that mitochondrial sorting of Kesv depends on a hierarchical combination of N- and C-terminal signals. Crucial is the length of the second transmembrane domain; extending its C terminus by > or = 2 hydrophobic amino acids redirects Kesv from the mitochondrial to the plasma membrane. Activity of Kesv in the plasma membrane is detected electrically or by yeast rescue assays only after this shift in sorting. Hence only minor structural alterations in a transmembrane domain are sufficient to switch sorting of a K(+) channel between the plasma membrane and mitochondria.
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45
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A yeast genetic screen reveals a critical role for the pore helix domain in TRP channel gating. Neuron 2008; 58:362-73. [PMID: 18466747 DOI: 10.1016/j.neuron.2008.04.012] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Revised: 03/13/2008] [Accepted: 04/11/2008] [Indexed: 11/20/2022]
Abstract
TRP cation channels function as cellular sensors in uni- and multicellular eukaryotes. Despite intensive study, the mechanisms of TRP channel activation by chemical or physical stimuli remain poorly understood. To identify amino acid residues crucial for TRP channel gating, we developed an unbiased, high-throughput genetic screen in yeast that uncovered rare, constitutively active mutants of the capsaicin receptor, TRPV1. We show that mutations within the pore helix domain dramatically increase basal channel activity and responsiveness to chemical and thermal stimuli. Mutation of corresponding residues within two related TRPV channels leads to comparable effects on their activation properties. Our data suggest that conformational changes in the outer pore region are critical for determining the balance between open and closed states, providing evidence for a general role for this domain in TRP channel activation.
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46
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Kawaguchi R, Yu J, Wiita P, Honda J, Sun H. An essential ligand-binding domain in the membrane receptor for retinol-binding protein revealed by large-scale mutagenesis and a human polymorphism. J Biol Chem 2008; 283:15160-8. [PMID: 18387951 PMCID: PMC2397481 DOI: 10.1074/jbc.m801060200] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Revised: 03/28/2008] [Indexed: 01/22/2023] Open
Abstract
Plasma retinol-binding protein (RBP), the principal carrier of vitamin A in the blood, delivers vitamin A from liver, the site of storage, to distant organs that need vitamin A, such as the eye, brain, placenta, and testis. STRA6 is a high-affinity membrane receptor for RBP and mediates vitamin A uptake in these target organs. STRA6 is a 74-kDa multi-transmembrane domain protein that represents a new class of membrane transport protein. In this study, we used an unbiased strategy by analyzing >900 random mutants of STRA6 to study its structure and function, and we identified an essential RBP-binding domain in STRA6. Mutations in any of the three essential residues in this domain can almost completely abolish binding of STRA6 to RBP and its vitamin A uptake activity from holo-RBP without affecting its cell surface expression. We have also functionally characterized the mutations in human STRA6 that cause severe birth defects as well as several human polymorphisms. All STRA6 mutants associated with severe birth defects have largely abolished vitamin A uptake activity, consistent with the severe clinical phenotypes. In addition, we have identified a human polymorphism that significantly reduces the vitamin A uptake activity of STRA6. Interestingly, the residue affected by this polymorphism is located in the RBP-binding domain we identified, and the polymorphism causes decreased vitamin A uptake by reducing RBP binding. This study identifies an essential functional domain in STRA6 and a human polymorphism in this domain that leads to reduced vitamin A uptake activity.
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Affiliation(s)
- Riki Kawaguchi
- Department of Physiology, the Jules Stein Eye Institute, and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095
| | - Jiamei Yu
- Department of Physiology, the Jules Stein Eye Institute, and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095
| | - Patrick Wiita
- Department of Physiology, the Jules Stein Eye Institute, and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095
| | - Jane Honda
- Department of Physiology, the Jules Stein Eye Institute, and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095
| | - Hui Sun
- Department of Physiology, the Jules Stein Eye Institute, and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095
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47
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Grabe M, Lai HC, Jain M, Jan YN, Jan LY. Structure prediction for the down state of a potassium channel voltage sensor. Nature 2006; 445:550-3. [PMID: 17187053 DOI: 10.1038/nature05494] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Accepted: 11/29/2006] [Indexed: 11/09/2022]
Abstract
Voltage-gated potassium (Kv) channels, essential for regulating potassium uptake and cell volume in plants and electrical excitability in animals, switch between conducting and non-conducting states as a result of conformational changes in the four voltage-sensing domains (VSDs) that surround the channel pore. This process, known as gating, is initiated by a cluster of positively charged residues on the fourth transmembrane segment (S4) of each VSD, which drives the VSD into a 'down state' at negative voltages and an 'up state' at more positive voltages. The crystal structure of Kv1.2 probably corresponds to the up state, but the local environment of S4 in the down state and its motion in voltage gating remains unresolved. Here we employed several conditional lethal/second-site suppressor yeast screens to determine the transmembrane packing of the VSD in the down state. This screen relies on the ability of KAT1, a eukaryotic Kv channel, to conduct potassium when its VSDs are in the down state, thereby rescuing potassium-transport-deficient yeast. Starting with KAT1 channels bearing conditional lethal mutations, we identified second-site suppressor mutations throughout the VSD that recover yeast growth. We then constructed a down state model of the channel using six pairs of interacting residues as structural constraints and verified this model by engineering suppressor mutations on the basis of spatial considerations. A comparison of this down state model with the up state Kv1.2 structure suggests that the VSDs undergo large rearrangements during gating, whereas the S4 segment remains positioned between the central pore and the remainder of the VSD in both states.
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Affiliation(s)
- Michael Grabe
- Department of Physiology, Howard Hughes Medical Institute
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48
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Pioletti M, Findeisen F, Hura GL, Minor DL. Three-dimensional structure of the KChIP1-Kv4.3 T1 complex reveals a cross-shaped octamer. Nat Struct Mol Biol 2006; 13:987-95. [PMID: 17057713 PMCID: PMC3018330 DOI: 10.1038/nsmb1164] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Accepted: 10/03/2006] [Indexed: 11/09/2022]
Abstract
Brain I(A) and cardiac I(to) currents arise from complexes containing Kv4 voltage-gated potassium channels and cytoplasmic calcium-sensor proteins (KChIPs). Here, we present X-ray crystallographic and small-angle X-ray scattering data that show that the KChIP1-Kv4.3 N-terminal cytoplasmic domain complex is a cross-shaped octamer bearing two principal interaction sites. Site 1 comprises interactions between a unique Kv4 channel N-terminal hydrophobic segment and a hydrophobic pocket formed by displacement of the KChIP H10 helix. Site 2 comprises interactions between a T1 assembly domain loop and the KChIP H2 helix. Functional and biochemical studies indicate that site 1 influences channel trafficking, whereas site 2 affects channel gating, and that calcium binding is intimately linked to KChIP folding and complex formation. Together, the data resolve how Kv4 channels and KChIPs interact and provide a framework for understanding how KChIPs modulate Kv4 function.
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Affiliation(s)
- Marta Pioletti
- Cardiovascular Research Institute, Department of Biochemistry, California Institute for Quantitative Biomedical Research, University of California, San Francisco, California 94143-2532, USA
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49
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Bichet D, Grabe M, Jan YN, Jan LY. Electrostatic interactions in the channel cavity as an important determinant of potassium channel selectivity. Proc Natl Acad Sci U S A 2006; 103:14355-60. [PMID: 16983069 PMCID: PMC1570129 DOI: 10.1073/pnas.0606660103] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Potassium channels are membrane proteins that allow the passage of potassium ions at near diffusion rates while severely limiting the flux of the slightly smaller sodium ions. Although studies thus far have focused on the narrowest part of the channel, known as the selectivity filter, channels are long pores with multiple ions that traverse the selectivity filter, the water-filled central cavity, and the rest of the pore formed by cytoplasmic domains. Here, we present experimental analyses on Kir3.2 (GIRK2), a G protein-activated inwardly rectifying potassium (Kir) channel, showing that a negative charge introduced at a pore-facing position in the cavity (N184) below the selectivity filter restores both K(+) selectivity and inward rectification properties to the nonselective S177W mutant channel. Molecular modeling demonstrates that the negative residue has no effect on the geometry of the selectivity filter, suggesting that it has a local effect on the cavity ion. Moreover, restoration of selectivity does not depend on the exact location of the charge in the central cavity as long as this residue faces the pore, where it is in close contact with permeant ions. Our results indicate that interactions between permeant ions and the channel cavity can influence ion selectivity and channel block by means of an electrostatic effect.
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Affiliation(s)
- Delphine Bichet
- Departments of Physiology and Biochemistry and Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
| | - Michael Grabe
- Departments of Physiology and Biochemistry and Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
| | - Yuh Nung Jan
- Departments of Physiology and Biochemistry and Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
| | - Lily Yeh Jan
- Departments of Physiology and Biochemistry and Howard Hughes Medical Institute, University of California, San Francisco, CA 94143
- To whom correspondence should be addressed. E-mail:
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50
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Grishin A, Li H, Levitan ES, Zaks-Makhina E. Identification of gamma-aminobutyric acid receptor-interacting factor 1 (TRAK2) as a trafficking factor for the K+ channel Kir2.1. J Biol Chem 2006; 281:30104-11. [PMID: 16895905 DOI: 10.1074/jbc.m602439200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To identify proteins that regulate potassium channel activity and expression, we performed functional screening of mammalian cDNA libraries in yeast that express the mammalian K(+) channel Kir2.1. Growth of Kir2.1-expressing yeast in media with low K(+) concentration is a function of K(+) uptake via Kir2.1 channels. Therefore, the host strain was transformed with a human cDNA library, and cDNA clones that rescued growth at low K(+) concentration were selected. One of these clones was identical to the protein of unknown function isolated previously as gamma-aminobutyric acid receptor-interacting factor 1 (GRIF-1) (Beck, M., Brickley, K., Wilkinson, H., Sharma, S., Smith, M., Chazot, P., Pollard, S., and Stephenson, F. (2002) J. Biol. Chem. 277, 30079-30090). GRIF-1 specifically enhanced Kir2.1-dependent growth in yeast and Kir2.1-mediated (86)Rb(+) efflux in HEK293 cells. Quantitative microscopy and flow cytometry analysis of immunolabeled surface Kir2.1 channel showed that GRIF-1 significantly increased the number of Kir2.1 channels in the plasma membrane of COS and HEK293 cells. Physical interaction of Kir2.1 channel and GRIF-1 was demonstrated by co-immunoprecipitation from HEK293 lysates and yeast two-hybrid assay. In vivo association of Kir2.1 and GRIF-1 was demonstrated by co-immunoprecipitation from brain lysate. Yeast two-hybrid assays showed that an N-terminal region of GRIF-1 interacts with a C-terminal region of Kir2.1. These results indicate that GRIF-1 binds to Kir2.1 and facilitates trafficking of this channel to the cell surface.
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Affiliation(s)
- Anatoly Grishin
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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