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Maksaev G, Bründl-Jirout M, Stary-Weinzinger A, Zangerl-Plessl EM, Lee SJ, Nichols CG. Subunit gating resulting from individual protonation events in Kir2 channels. Nat Commun 2023; 14:4538. [PMID: 37507406 PMCID: PMC10382558 DOI: 10.1038/s41467-023-40058-7] [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: 04/07/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
Inwardly rectifying potassium (Kir) channels open at the 'helix bundle crossing' (HBC), formed by the M2 helices at the cytoplasmic end of the transmembrane pore. Introduced negative charges at the HBC (G178D) in Kir2.2 channels forces opening, allowing pore wetting and free movement of permeant ions between the cytoplasm and the inner cavity. Single-channel recordings reveal striking, pH-dependent, subconductance behaviors in G178D (or G178E and equivalent Kir2.1[G177E]) mutant channels, with well-resolved non-cooperative subconductance levels. Decreasing cytoplasmic pH shifts the probability towards lower conductance levels. Molecular dynamics simulations show how protonation of Kir2.2[G178D], or the D173 pore-lining residues, changes solvation, K+ ion occupancy, and K+ conductance. Ion channel gating and conductance are classically understood as separate processes. The present data reveal how individual protonation events change the electrostatic microenvironment of the pore, resulting in step-wise alterations of ion pooling, and hence conductance, that appear as 'gated' substates.
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Affiliation(s)
- Grigory Maksaev
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael Bründl-Jirout
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Eva-Maria Zangerl-Plessl
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria.
| | - Sun-Joo Lee
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Colin G Nichols
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA.
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2
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Maksaev G, Bründl-Jirout M, Stary-Weinzinger A, Zangerl-Plessl EM, Lee SJ, Nichols CG. Subunit gating resulting from individual protonation events in Kir2 channels. RESEARCH SQUARE 2023:rs.3.rs-2640647. [PMID: 36993294 PMCID: PMC10055540 DOI: 10.21203/rs.3.rs-2640647/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Inwardly rectifying potassium (Kir) channels play a critical role in stabilizing the membrane potential, thus controlling numerous physiological phenomena in multiple tissues. Channel conductance is activated by cytoplasmic modulators that open the channel at the 'helix bundle crossing' (HBC), formed by the coming together of the M2 helices from each of the four subunits, at the cytoplasmic end of the transmembrane pore. We introduced a negative charge at the bundle crossing region (G178D) in classical inward rectifier Kir2.2 channel subunits that forces channel opening, allowing pore wetting and free movement of permeant ions between the cytoplasm and the inner cavity. Single-channel recordings reveal a striking pH-dependent subconductance behavior in G178D (or G178E and equivalent Kir2.1[G177E]) mutant channels that reflects individual subunit events. These subconductance levels are well resolved temporally and occur independently, with no evidence of cooperativity. Decreasing cytoplasmic pH shifts the probability towards lower conductance levels, and molecular dynamics simulations show how protonation of Kir2.2[G178D] and, additionally, the rectification controller (D173) pore-lining residues leads to changes in pore solvation, K+ ion occupancy, and ultimately K+ conductance. While subconductance gating has long been discussed, resolution and explanation have been lacking. The present data reveals how individual protonation events change the electrostatic microenvironment of the pore, resulting in distinct, uncoordinated, and relatively long-lasting conductance states, which depend on levels of ion pooling in the pore and the maintenance of pore wetting. Gating and conductance are classically understood as separate processes in ion channels. The remarkable sub-state gating behavior of these channels reveals how intimately connected 'gating' and 'conductance' are in reality.
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Affiliation(s)
- Grigory Maksaev
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael Bründl-Jirout
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Eva-Maria Zangerl-Plessl
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Sun-Joo Lee
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
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3
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Lee SJ, Nichols CG. Seeing spermine blocking of K+ ion movement through inward rectifier Kir2.2 channels. J Gen Physiol 2022; 155:213764. [PMID: 36524992 PMCID: PMC9764022 DOI: 10.1085/jgp.202213144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Inwardly rectifier potassium (Kir) channels are a major potassium channel sub-class whose function is regulated by ligand-dependent gating and highly voltage-dependent block by polyamines. With molecular dynamics simulations over previously unattainable timescales, Jogini et al. (J. Gen. Physiol. https://doi.org/10.1085/jgp.202213085) provide unprecedented visualization of K+ conduction through open Kir2.2 channels and of the molecular details of channel block by spermine.
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Affiliation(s)
- Sun-Joo Lee
- Department of Cell Biology and Physiology, Center for Investigation of Membrane Excitability Diseases, Washington University in. St. Louis, St. Louis, MO, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology, Center for Investigation of Membrane Excitability Diseases, Washington University in. St. Louis, St. Louis, MO, USA,Correspondence to Colin G. Nichols:
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Sagar NA, Tarafdar S, Agarwal S, Tarafdar A, Sharma S. Polyamines: Functions, Metabolism, and Role in Human Disease Management. Med Sci (Basel) 2021; 9:44. [PMID: 34207607 PMCID: PMC8293435 DOI: 10.3390/medsci9020044] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Revised: 06/05/2021] [Accepted: 06/07/2021] [Indexed: 12/11/2022] Open
Abstract
Putrescine, spermine, and spermidine are the important polyamines (PAs), found in all living organisms. PAs are formed by the decarboxylation of amino acids, and they facilitate cell growth and development via different cellular responses. PAs are the integrated part of the cellular and genetic metabolism and help in transcription, translation, signaling, and post-translational modifications. At the cellular level, PA concentration may influence the condition of various diseases in the body. For instance, a high PA level is detrimental to patients suffering from aging, cognitive impairment, and cancer. The levels of PAs decline with age in humans, which is associated with different health disorders. On the other hand, PAs reduce the risk of many cardiovascular diseases and increase longevity, when taken in an optimum quantity. Therefore, a controlled diet is an easy way to maintain the level of PAs in the body. Based on the nutritional intake of PAs, healthy cell functioning can be maintained. Moreover, several diseases can also be controlled to a higher extend via maintaining the metabolism of PAs. The present review discusses the types, important functions, and metabolism of PAs in humans. It also highlights the nutritional role of PAs in the prevention of various diseases.
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Affiliation(s)
- Narashans Alok Sagar
- Department of Agriculture and Environmental Sciences, National Institute of Food Technology Entrepreneurship and Management, Kundli, Sonepat 131028, Haryana, India
- Food Microbiology Lab, Division of Livestock Products Technology, ICAR-Indian Veterinary Research Institute, Izatnagar 243122, Uttar Pradesh, India
| | - Swarnava Tarafdar
- Department of Radiodiagnosis and Imaging, All India Institute of Medical Science, Rishikesh 249203, Uttarakhand, India;
| | - Surbhi Agarwal
- Department of Hematology, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India;
| | - Ayon Tarafdar
- Livestock Production and Management Section, ICAR-Indian Veterinary Research Institute, Izatnagar 243122, Uttar Pradesh, India;
| | - Sunil Sharma
- Department of Agriculture and Environmental Sciences, National Institute of Food Technology Entrepreneurship and Management, Kundli, Sonepat 131028, Haryana, India
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5
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Kurata HT. Unconventional voltage sensing in an inwardly rectifying potassium channel. J Gen Physiol 2021; 153:212077. [PMID: 33956072 PMCID: PMC8105720 DOI: 10.1085/jgp.202112929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Affiliation(s)
- Harley T Kurata
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
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6
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Zangerl-Plessl EM, Lee SJ, Maksaev G, Bernsteiner H, Ren F, Yuan P, Stary-Weinzinger A, Nichols CG. Atomistic basis of opening and conduction in mammalian inward rectifier potassium (Kir2.2) channels. J Gen Physiol 2021; 152:jgp.201912422. [PMID: 31744859 PMCID: PMC7034095 DOI: 10.1085/jgp.201912422] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022] Open
Abstract
This paper presents the crystal structure of a forced open inward rectifier Kir2.2 channel. Molecular dynamics reveals the details of ion permeation through the open channel. Potassium ion conduction through open potassium channels is essential to control of membrane potentials in all cells. To elucidate the open conformation and hence the mechanism of K+ ion conduction in the classic inward rectifier Kir2.2, we introduced a negative charge (G178D) at the crossing point of the inner helix bundle, the location of ligand-dependent gating. This “forced open” mutation generated channels that were active even in the complete absence of phosphatidylinositol-4,5-bisphosphate (PIP2), an otherwise essential ligand for Kir channel opening. Crystal structures were obtained at a resolution of 3.6 Å without PIP2 bound, or 2.8 Å in complex with PIP2. The latter revealed a slight widening at the helix bundle crossing (HBC) through backbone movement. MD simulations showed that subsequent spontaneous wetting of the pore through the HBC gate region allowed K+ ion movement across the HBC and conduction through the channel. Further simulations reveal atomistic details of the opening process and highlight the role of pore-lining acidic residues in K+ conduction through Kir2 channels.
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Affiliation(s)
| | - Sun-Joo Lee
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO
| | - Grigory Maksaev
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO
| | - Harald Bernsteiner
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Feifei Ren
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO
| | - Peng Yuan
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO
| | | | - Colin G Nichols
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO
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7
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Abstract
Potassium channels that exhibit the property of inward rectification (Kir channels) are present in most cells. Cloning of the first Kir channel genes 25 years ago led to recognition that inward rectification is a consequence of voltage-dependent block by cytoplasmic polyamines, which are also ubiquitously present in animal cells. Upon cellular depolarization, these polycationic metabolites enter the Kir channel pore from the intracellular side, blocking the movement of K+ ions through the channel. As a consequence, high K+ conductance at rest can provide very stable negative resting potentials, but polyamine-mediated blockade at depolarized potentials ensures, for instance, the long plateau phase of the cardiac action potential, an essential feature for a stable cardiac rhythm. Despite much investigation of the polyamine block, where exactly polyamines get to within the Kir channel pore and how the steep voltage dependence arises remain unclear. This Minireview will summarize current understanding of the relevance and molecular mechanisms of polyamine block and offer some ideas to try to help resolve the fundamental issue of the voltage dependence of polyamine block.
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Affiliation(s)
- Colin G Nichols
- From the Department of Cell Biology and Physiology, Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, Missouri 63110
| | - Sun-Joo Lee
- From the Department of Cell Biology and Physiology, Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, Missouri 63110
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Borschel WF, Wang S, Lee S, Nichols CG. Control of Kir channel gating by cytoplasmic domain interface interactions. J Gen Physiol 2017; 149:561-576. [PMID: 28389584 PMCID: PMC5412532 DOI: 10.1085/jgp.201611719] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 12/29/2016] [Accepted: 03/01/2017] [Indexed: 12/19/2022] Open
Abstract
The pore-forming unit of ATP-sensitive K channels is composed of four Kir6.2 subunits. Borschel et al. show that salt bridges between the cytoplasmic domain of adjacent Kir6.2 subunits determine the degree to which channels inactivate after removal of ATP. Inward rectifier potassium (Kir) channels are expressed in almost all mammalian tissues and play critical roles in the control of excitability. Pancreatic ATP-sensitive K (KATP) channels are key regulators of insulin secretion and comprise Kir6.2 subunits coupled to sulfonylurea receptors. Because these channels are reversibly inhibited by cytoplasmic ATP, they link cellular metabolism with membrane excitability. Loss-of-function mutations in the pore-forming Kir6.2 subunit cause congenital hyperinsulinism as a result of diminished channel activity. Here, we show that several disease mutations, which disrupt intersubunit salt bridges at the interface of the cytoplasmic domains (CD-I) of adjacent subunits, induce loss of channel activity via a novel channel behavior: after ATP removal, channels open but then rapidly inactivate. Re-exposure to inhibitory ATP causes recovery from this inactivation. Inactivation can be abolished by application of phosphatidylinositol-4,5-bisphosphate (PIP2) to the cytoplasmic face of the membrane, an effect that can be explained by a simple kinetic model in which PIP2 binding competes with the inactivation process. Kir2.1 channels contain homologous salt bridges, and we find that mutations that disrupt CD-I interactions in Kir2.1 also reduce channel activity and PIP2 sensitivity. Kir2.1 channels also contain an additional CD-I salt bridge that is not present in Kir6.2 channels. Introduction of this salt bridge into Kir6.2 partially rescues inactivating mutants from the phenotype. These results indicate that the stability of the intersubunit CD-I is a major determinant of the inactivation process in Kir6.2 and may control gating in other Kir channels.
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Affiliation(s)
- William F Borschel
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Shizhen Wang
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Sunjoo Lee
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 .,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
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9
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Abstract
The content of spermidine and spermine in mammalian cells has important roles in protein and nucleic acid synthesis and structure, protection from oxidative damage, activity of ion channels, cell proliferation, differentiation, and apoptosis. Spermidine is essential for viability and acts as the precursor of hypusine, a post-translational addition to eIF5A allowing the translation of mRNAs encoding proteins containing polyproline tracts. Studies with Gy mice and human patients with the very rare X-linked genetic condition Snyder-Robinson syndrome that both lack spermine synthase show clearly that the correct spermine:spermidine ratio is critical for normal growth and development.
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Affiliation(s)
- Anthony E Pegg
- From the Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
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10
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Méndez-González MP, Kucheryavykh YV, Zayas-Santiago A, Vélez-Carrasco W, Maldonado-Martínez G, Cubano LA, Nichols CG, Skatchkov SN, Eaton MJ. Novel KCNJ10 Gene Variations Compromise Function of Inwardly Rectifying Potassium Channel 4.1. J Biol Chem 2016; 291:7716-26. [PMID: 26867573 PMCID: PMC4817196 DOI: 10.1074/jbc.m115.679910] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Revised: 02/09/2016] [Indexed: 11/06/2022] Open
Abstract
TheKCNJ10gene encoding Kir4.1 contains numerous SNPs whose molecular effects remain unknown. We investigated the functional consequences of uncharacterized SNPs (Q212R, L166Q, and G83V) on homomeric (Kir4.1) and heteromeric (Kir4.1-Kir5.1) channel function. We compared these with previously characterized EAST/SeSAME mutants (G77R and A167V) in kidney-derived tsA201 cells and in glial cell-derived C6 glioma cells. The membrane potentials of tsA201 cells expressing G77R and G83V were significantly depolarized as compared with WTKir4.1, whereas cells expressing Q212R, L166Q, and A167V were less affected. Furthermore, macroscopic currents from cells expressing WTKir4.1 and Q212R channels did not differ, whereas currents from cells expressing L166Q, G83V, G77R, and A167V were reduced. Unexpectedly, L166Q current responses were rescued when co-expressed with Kir5.1. In addition, we observed notable differences in channel activity between C6 glioma cells and tsA201 cells expressing L166Q and A167V, suggesting that there are underlying differences between cell lines in terms of Kir4.1 protein synthesis, stability, or expression at the surface. Finally, we determined spermine (SPM) sensitivity of these uncharacterized SNPs and found that Q212R-containing channels displayed reduced block by 1 μmSPM. At 100 μmSPM, the block was equal to or greater than WT, suggesting that the greater driving force of SPM allowed achievement of steady state. In contrast, L166Q-Kir5.1 channels achieved a higher block than WT, suggesting a more stable interaction of SPM in the deep pore cavity. Overall, our data suggest that G83V, L166Q, and Q212R residues play a pivotal role in controlling Kir4.1 channel function.
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Affiliation(s)
| | | | | | | | | | - Luis A Cubano
- Anatomy and Cell Biology, Universidad Central del Caribe, Bayamón, Puerto Rico 00960-6032 and
| | - Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093
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11
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A synergistic blocking effect of Mg²⁺ and spermine on the inward rectifier K⁺ (Kir2.1) channel pore. Sci Rep 2016; 6:21493. [PMID: 26869275 PMCID: PMC4751470 DOI: 10.1038/srep21493] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 01/25/2016] [Indexed: 11/23/2022] Open
Abstract
Inward rectifier K+ channels (Kir2.1) exhibit an extraordinary rectifying feature in the current–voltage relationship. We have previously showed that the bundle–crossing region of the transmembrane domain constitutes the crucial segment responsible for the polyamine block. In this study, we demonstrated that the major blocking effect of intracellular Mg2+ on Kir2.1 channels is also closely correlated with K+ current flow, and the coupled movements of Mg2+ and K+ seem to happen in the same flux–coupling segment of the pore as polyamines. With a preponderant outward K+ flow, intracellular Mg2+ would also be pushed to and thus stay at the outermost site of a flux–coupling segment in the bundle–crossing region of Kir2.1 channels to block the pore, although with a much lower apparent affinity than spermine (SPM). However, in contrast to the evident possibilities of outward exit of SPM through the channel pore especially during strong membrane depolarization, intracellular Mg2+ does not seem to traverse the Kir2.1 channel pore in any case. Intracellular Mg2+ and SPM therefore may have a synergistic action on the pore–blocking effect, presumably via prohibition of the outward exit of the higher–affinity blocking SPM by the lower–affinity Mg2+.
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12
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Chang HK, Iwamoto M, Oiki S, Shieh RC. Mechanism for attenuated outward conductance induced by mutations in the cytoplasmic pore of Kir2.1 channels. Sci Rep 2015; 5:18404. [PMID: 26678093 PMCID: PMC4683409 DOI: 10.1038/srep18404] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/18/2015] [Indexed: 01/12/2023] Open
Abstract
Outward currents through Kir2.1 channels regulate the electrical properties of excitable cells. These currents are subject to voltage-dependent attenuation by the binding of polyamines to high- and low-affinity sites, which leads to inward rectification, thereby controlling cell excitability. To examine the effects of positive charges at the low-affinity site in the cytoplasmic pore on inward rectification, we studied a mutant Kir channel (E224K/H226E) and measured single-channel currents and streaming potentials (Vstream), the latter provide the ratio of water to ions queued in a single-file permeation process in the selectivity filter. The water-ion coupling ratio was near one at a high K+ concentration ([K+]) for the wild-type channel and increased substantially as [K+] decreased. On the other hand, fewer ions occupied the selectivity filter in the mutant at all [K+]. A model for the Kir channel involving a K+ binding site in the wide pore was introduced. Model analyses revealed that the rate constants associated with the binding and release to and from the wide-pore K+ binding site was modified in the mutant. These effects lead to the reduced contribution of a conventional two-ion permeation mode to total conductance, especially at positive potentials, thereby inward rectification.
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Affiliation(s)
- Hsueh-Kai Chang
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC
| | - Masayuki Iwamoto
- Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan
| | - Shigetoshi Oiki
- Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC
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13
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Huang CW, Kuo CC. Gating of the kir2.1 channel at the bundle crossing region by intracellular spermine and other cations. J Cell Physiol 2014; 229:1703-21. [PMID: 24633623 DOI: 10.1002/jcp.24616] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 03/12/2014] [Indexed: 11/06/2022]
Abstract
In the Kir2.1 channel, the flow-dependent blocking effect of intracellular spermine (SPM) strongly indicates coupled movement of ions in a segment of the pore. We have shown that the bundle crossing region of M2 constitutes this critical segment of the pore. Moreover, this segment may undergo opening/closing conformational changes mimicking channel gating. In this study, we further investigate these "gating" conformational changes and relevant controlling mechanisms at this critical segment. We demonstrate that A184R mutation in the inner end of the bundle crossing region not only abolishes the inward rectifying features of SPM block but also tends to close the channel pore, which can then only be opened by intracellular (e.g., Na(+) , or equally effectively, K(+) ) but not extracellular cations. We also found that the exit (back to the intracellular milieu) of the blocking in the deep site is facilitated rather than deterred by the presence of the other SPM in the superficial site. We conclude that intracellular SPM may bind to a deep site in the pore and serve as a flow-dependent blocker. The SPM in the superficial site, on the other hand, serves both as a docking form ready for permeation to the deep site, and as a gating particle capable of opening the bundle crossing region. This inner end of the bundle crossing region of the Kir2.1 channel pore thus constitutes a pivotal segment, which, in collaboration with intracellular SPM and K(+) ions, closely couple channel gating to (inward rectifying) ion permeation.
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Affiliation(s)
- Chiung-Wei Huang
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan
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14
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Baronas VA, Kurata HT. Inward rectifiers and their regulation by endogenous polyamines. Front Physiol 2014; 5:325. [PMID: 25221519 PMCID: PMC4145359 DOI: 10.3389/fphys.2014.00325] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Accepted: 08/06/2014] [Indexed: 12/02/2022] Open
Abstract
Inwardly-rectifying potassium (Kir) channels contribute to maintenance of the resting membrane potential and regulation of electrical excitation in many cell types. Strongly rectifying Kir channels exhibit a very steep voltage dependence resulting in silencing of their activity at depolarized membrane voltages. The mechanism underlying this steep voltage dependence is blockade by endogenous polyamines. These small multifunctional, polyvalent metabolites enter the long Kir channel pore from the intracellular side, displacing multiple occupant ions as they migrate to a stable binding site in the transmembrane region of the channel. Numerous structure-function studies have revealed structural elements of Kir channels that determine their susceptibility to polyamine block, and enable the steep voltage dependence of this process. In addition, various channelopathies have been described that result from alteration of the polyamine sensitivity or activity of strongly rectifying channels. The primary focus of this article is to summarize current knowledge of the molecular mechanisms of polyamine block, and provide some perspective on lingering uncertainties related to this physiologically important mechanism of ion channel blockade. We also briefly review some of the important and well understood physiological roles of polyamine sensitive, strongly rectifying Kir channels, primarily of the Kir2 family.
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Affiliation(s)
- Victoria A Baronas
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia Vancouver, BC, Canada
| | - Harley T Kurata
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia Vancouver, BC, Canada
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15
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Pottosin I, Shabala S. Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling. FRONTIERS IN PLANT SCIENCE 2014; 5:154. [PMID: 24795739 PMCID: PMC4006063 DOI: 10.3389/fpls.2014.00154] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 04/02/2014] [Indexed: 05/18/2023]
Abstract
Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm(4+) > Spd(3+) > Put(2+). On the contrary, effects of polyamines on the plasma membrane (PM) cation and K(+)-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H(+) pumps and Ca(2+) pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca(2+) influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment.
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Affiliation(s)
- Igor Pottosin
- Biomedical Centre, Centro Universitario de Investigaciones Biomédicas, University of ColimaColima, Mexico
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
| | - Sergey Shabala
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
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Vilin YY, Nunez JJ, Kim RY, Dake GR, Kurata HT. Paradoxical Activation of an Inwardly Rectifying Potassium Channel Mutant by Spermine: "(B)locking" Open the Bundle Crossing Gate. Mol Pharmacol 2013; 84:572-81. [DOI: 10.1124/mol.113.086603] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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The bundle crossing region is responsible for the inwardly rectifying internal spermine block of the Kir2.1 channel. Pflugers Arch 2013; 466:275-93. [PMID: 23873351 DOI: 10.1007/s00424-013-1322-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 05/03/2013] [Accepted: 06/24/2013] [Indexed: 10/26/2022]
Abstract
Inward rectifier potassium channels conduct K(+) across the cell membrane more efficiently in the inward than outward direction in physiological conditions. Voltage-dependent and flow-dependent blocks of outward K(+) currents by intracellular polyamines (e.g., spermine (SPM)) have been proposed as the major mechanisms underlying inward rectification. In this study, we show that the SPM blocking affinity curve is shifted according to the shift in K(+) reversal potential. Moreover, the kinetics of SPM entry to and exit from the binding site are correlatively slowed by specific E224 and E299 mutations, which always also disrupt the flux coupling feature of SPM block. The entry rates carry little voltage dependence, whereas the exit rates are e-fold decelerated per ∼15 mV depolarization. Interestingly, the voltage dependence remains rather constant among WT and quite a few different mutant channels. This voltage dependence offers an unprecedented chance of mapping the location (electrical distance) of the SPM site in the pore because these kinetic data were obtained along the preponderant direction of K(+) current flow (outward currents for the entry rate and inward currents for the exit rate) and thus contamination from flow dependence should be negligible. Moreover, double mutations involving E224 and A178 or M183 seem to alter the height of the same asymmetrical barrier between the SPM binding site and the intracellular milieu. We conclude that the SPM site responsible for the inward rectifying block is located at an electrical distance of ∼0.5 from the inside and is involved in a flux coupling segment in the bundle crossing region of the pore. With preponderant outward K(+) flow, SPM is "pushed" to the outmost site of this segment (∼D172). On the other hand, the blocking SPM would be pushed to the inner end of this segment (∼M183-A184) with preponderant inward K(+) flow. Moreover, E224 and E299 very likely electrostatically interact with the other residues (e.g., R228, R260) in the cytoplasmic domain and then allosterically keep the bundle crossing region in an open conformation appropriate for the flux coupling block of SPM.
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Kurata HT, Akrouh A, Li JBW, Marton LJ, Nichols CG. Scanning the topography of polyamine blocker binding in an inwardly rectifying potassium channel. J Biol Chem 2013; 288:6591-601. [PMID: 23300089 DOI: 10.1074/jbc.m112.383794] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Steeply voltage-dependent inward rectification of Kir (inwardly rectifying potassium) channels arises from blockade by cytoplasmic polyamines. These polycationic blockers traverse a long (>70 Å) pore, displacing multiple permeant ions, en route to a high affinity binding site that remains loosely defined. We have scanned the effects of cysteine modification at multiple pore-lining positions on the blocking properties of a library of polyamine analogs, demonstrating that the effects of cysteine modification are position- and blocker-dependent. Specifically, introduction of positively charged adducts results in two distinct phenotypes: either disruption of blocker binding or generation of a barrier to blocker migration, in a consistent pattern that depends on both the length of the polyamine blocker and the position of the modified cysteine. These findings reveal important details about the chemical basis and specific location of high affinity polyamine binding.
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Affiliation(s)
- Harley T Kurata
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
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Mechanisms for Kir channel inhibition by quinacrine: acute pore block of Kir2.x channels and interference in PIP2 interaction with Kir2.x and Kir6.2 channels. Pflugers Arch 2011; 462:505-17. [DOI: 10.1007/s00424-011-0995-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 07/08/2011] [Accepted: 07/08/2011] [Indexed: 10/18/2022]
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