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Nordquist E, Zhang G, Barethiya S, Ji N, White KM, Han L, Jia Z, Shi J, Cui J, Chen J. Incorporating physics to overcome data scarcity in predictive modeling of protein function: A case study of BK channels. PLoS Comput Biol 2023; 19:e1011460. [PMID: 37713443 PMCID: PMC10529646 DOI: 10.1371/journal.pcbi.1011460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Revised: 09/27/2023] [Accepted: 08/24/2023] [Indexed: 09/17/2023] Open
Abstract
Machine learning has played transformative roles in numerous chemical and biophysical problems such as protein folding where large amount of data exists. Nonetheless, many important problems remain challenging for data-driven machine learning approaches due to the limitation of data scarcity. One approach to overcome data scarcity is to incorporate physical principles such as through molecular modeling and simulation. Here, we focus on the big potassium (BK) channels that play important roles in cardiovascular and neural systems. Many mutants of BK channel are associated with various neurological and cardiovascular diseases, but the molecular effects are unknown. The voltage gating properties of BK channels have been characterized for 473 site-specific mutations experimentally over the last three decades; yet, these functional data by themselves remain far too sparse to derive a predictive model of BK channel voltage gating. Using physics-based modeling, we quantify the energetic effects of all single mutations on both open and closed states of the channel. Together with dynamic properties derived from atomistic simulations, these physical descriptors allow the training of random forest models that could reproduce unseen experimentally measured shifts in gating voltage, ∆V1/2, with a RMSE ~ 32 mV and correlation coefficient of R ~ 0.7. Importantly, the model appears capable of uncovering nontrivial physical principles underlying the gating of the channel, including a central role of hydrophobic gating. The model was further evaluated using four novel mutations of L235 and V236 on the S5 helix, mutations of which are predicted to have opposing effects on V1/2 and suggest a key role of S5 in mediating voltage sensor-pore coupling. The measured ∆V1/2 agree quantitatively with prediction for all four mutations, with a high correlation of R = 0.92 and RMSE = 18 mV. Therefore, the model can capture nontrivial voltage gating properties in regions where few mutations are known. The success of predictive modeling of BK voltage gating demonstrates the potential of combining physics and statistical learning for overcoming data scarcity in nontrivial protein function prediction.
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Affiliation(s)
- Erik Nordquist
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America
| | - Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Shrishti Barethiya
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America
| | - Nathan Ji
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, United States of America
| | - Kelli M. White
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Lu Han
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America
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2
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Nordquist E, Zhang G, Barethiya S, Ji N, White KM, Han L, Jia Z, Shi J, Cui J, Chen J. Incorporating physics to overcome data scarcity in predictive modeling of protein function: a case study of BK channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.24.546384. [PMID: 37425916 PMCID: PMC10327070 DOI: 10.1101/2023.06.24.546384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
Machine learning has played transformative roles in numerous chemical and biophysical problems such as protein folding where large amount of data exists. Nonetheless, many important problems remain challenging for data-driven machine learning approaches due to the limitation of data scarcity. One approach to overcome data scarcity is to incorporate physical principles such as through molecular modeling and simulation. Here, we focus on the big potassium (BK) channels that play important roles in cardiovascular and neural systems. Many mutants of BK channel are associated with various neurological and cardiovascular diseases, but the molecular effects are unknown. The voltage gating properties of BK channels have been characterized for 473 site-specific mutations experimentally over the last three decades; yet, these functional data by themselves remain far too sparse to derive a predictive model of BK channel voltage gating. Using physics-based modeling, we quantify the energetic effects of all single mutations on both open and closed states of the channel. Together with dynamic properties derived from atomistic simulations, these physical descriptors allow the training of random forest models that could reproduce unseen experimentally measured shifts in gating voltage, ΔV 1/2 , with a RMSE ∼ 32 mV and correlation coefficient of R ∼ 0.7. Importantly, the model appears capable of uncovering nontrivial physical principles underlying the gating of the channel, including a central role of hydrophobic gating. The model was further evaluated using four novel mutations of L235 and V236 on the S5 helix, mutations of which are predicted to have opposing effects on V 1/2 and suggest a key role of S5 in mediating voltage sensor-pore coupling. The measured ΔV 1/2 agree quantitatively with prediction for all four mutations, with a high correlation of R = 0.92 and RMSE = 18 mV. Therefore, the model can capture nontrivial voltage gating properties in regions where few mutations are known. The success of predictive modeling of BK voltage gating demonstrates the potential of combining physics and statistical learning for overcoming data scarcity in nontrivial protein function prediction. Author Summary Deep machine learning has brought many exciting breakthroughs in chemistry, physics and biology. These models require large amount of training data and struggle when the data is scarce. The latter is true for predictive modeling of the function of complex proteins such as ion channels, where only hundreds of mutational data may be available. Using the big potassium (BK) channel as a biologically important model system, we demonstrate that a reliable predictive model of its voltage gating property could be derived from only 473 mutational data by incorporating physics-derived features, which include dynamic properties from molecular dynamics simulations and energetic quantities from Rosetta mutation calculations. We show that the final random forest model captures key trends and hotspots in mutational effects of BK voltage gating, such as the important role of pore hydrophobicity. A particularly curious prediction is that mutations of two adjacent residues on the S5 helix would always have opposite effects on the gating voltage, which was confirmed by experimental characterization of four novel mutations. The current work demonstrates the importance and effectiveness of incorporating physics in predictive modeling of protein function with scarce data.
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Affiliation(s)
- Erik Nordquist
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Shrishti Barethiya
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Nathan Ji
- Department of Biology, Boston College, Chestnut Hill, Massachusetts, USA
| | - Kelli M. White
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Lu Han
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts, USA
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3
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Lüke JN, Neumaier F, Alpdogan S, Hescheler J, Schneider T, Albanna W, Akhtar-Schäfer I. Submicromolar copper (II) ions stimulate transretinal signaling in the isolated retina from wild type but not from Ca v2.3-deficient mice. BMC Ophthalmol 2020; 20:182. [PMID: 32375703 PMCID: PMC7201970 DOI: 10.1186/s12886-020-01451-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Accepted: 04/24/2020] [Indexed: 05/30/2023] Open
Abstract
BACKGROUND So far, only indirect evidence exists for the pharmacoresistant R-type voltage-gated Ca2+ channel (VGCC) to be involved in transretinal signaling by triggering GABA-release onto ON-bipolar neurons. This release of inhibitory neurotransmitters was deduced from the sensitivity of the b-wave to stimulation by Ni2+, Zn2+ and Cu2+. To further confirm the interpretation of these findings, we compared the effects of Cu2+ application and chelation (using kainic acid, KA) on the neural retina from wildtype and Cav2.3-deficient mice. Furthermore, the immediately effect of KA on the ERG b-wave modulation was assessed. METHODS Transretinal signaling was recorded as an ERG from the superfused murine retina isolated from wildtype and Cav2.3-deficient mice. RESULTS In mice, the stimulating effect of 100 nM CuCl2 is absent in the retinae from Cav2.3-deficient mice, but prominent in Cav2.3-competent mice. Application of up to 3 mM tricine does not affect the murine b-wave in both genotypes, most likely because of chelating amino acids present in the murine nutrient solution. Application of 27 μM KA significantly increased the b-wave amplitude in wild type and Cav2.3 (-|-) mice. This effect can most likely be explained by the stimulation of endogenous KA-receptors described in horizontal, OFF-bipolar, amacrine or ganglion cells, which could not be fully blocked in the present study. CONCLUSION Cu2+-dependent modulation of transretinal signaling only occurs in the murine retina from Cav2.3 competent mice, supporting the ideas derived from previous work in the bovine retina that R-type Ca2+ channels are involved in shaping transretinal responses during light perception.
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Affiliation(s)
- Jan Niklas Lüke
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany
| | - Felix Neumaier
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany
| | - Serdar Alpdogan
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany
| | - Jürgen Hescheler
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany
| | - Toni Schneider
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany.
| | - Walid Albanna
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany. .,Department of Neurosurgery, University Hospital, RWTH Aachen, Aachen, Germany.
| | - Isha Akhtar-Schäfer
- Institute for Neurophysiology, University of Cologne, Robert-Koch Str. 39, D-50931, Cologne, Germany
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Bassetto CAZ, Carvalho-de-Souza JL, Bezanilla F. Metal Bridge in S4 Segment Supports Helix Transition in Shaker Channel. Biophys J 2019; 118:922-933. [PMID: 31635788 DOI: 10.1016/j.bpj.2019.08.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 08/22/2019] [Accepted: 08/29/2019] [Indexed: 02/05/2023] Open
Abstract
Voltage-gated ion channels play important roles in physiological processes, especially in excitable cells, in which they shape the action potential. In S4-based voltage sensors voltage-gated channels, a common feature is shared; the transmembrane segment 4 (S4) contains positively charged residues intercalated by hydrophobic residues. Although several advances have been made in understating how S4 moves through a hydrophobic plug upon voltage changes, the possible helix transition from α- to 310-helix in S4 during the activation process is still unresolved. Here, we have mutated several hydrophobic residues from I360 to F370 in the S4 segment into histidine, in i, i + 3 and i, i + 6 or i, i + 4 and i, i + 7 pairs, to favor 310- or α-helical conformations, respectively. We have taken advantage of the ability of His to coordinate Zn2+ to promote metal ion bridges, and we have found that the histidine introduced at position 366 (L366H) can interact with the introduced histidine at position 370 (stabilizing that portion of the S4 segment in α-helical conformation). In the presence of 20 μM of Zn2+, the activation currents of L366H:F370H channels were slowed down by a factor of 3.5, and the voltage dependence is shifted by 10 mV toward depolarized potentials with no change on the deactivation time constant. Our data supports that by stabilizing a region of the S4 segment in α-helical conformation, a closed (resting or intermediate) state is stabilized rather than destabilizing the open (active) state. Taken together, our data indicates that S4 undergoes α-helical conformation to a short-lived different secondary structure transiently before reaching the active state in the activation process.
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Affiliation(s)
- Carlos A Z Bassetto
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois
| | | | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois; Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois; Centro Interdisciplinario de Neurociencias, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
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5
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Penkauskas T, Preta G. Biological applications of tethered bilayer lipid membranes. Biochimie 2019; 157:131-141. [DOI: 10.1016/j.biochi.2018.11.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 11/19/2018] [Indexed: 12/16/2022]
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6
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Yamada Y, Prosser RA. Copper in the suprachiasmatic circadian clock: A possible link between multiple circadian oscillators. Eur J Neurosci 2018; 51:47-70. [PMID: 30269387 DOI: 10.1111/ejn.14181] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 09/05/2018] [Accepted: 09/17/2018] [Indexed: 01/07/2023]
Abstract
The mammalian circadian clock in the suprachiasmatic nucleus (SCN) is very robust, able to coordinate our daily physiological and behavioral rhythms with exquisite accuracy. Simultaneously, the SCN clock is highly sensitive to environmental timing cues such as the solar cycle. This duality of resiliency and sensitivity may be sustained in part by a complex intertwining of three cellular oscillators: transcription/translation, metabolic/redox, and membrane excitability. We suggest here that one of the links connecting these oscillators may be forged from copper (Cu). Cellular Cu levels are highly regulated in the brain and peripherally, and Cu affects cellular metabolism, redox state, cell signaling, and transcription. We have shown that both Cu chelation and application induce nighttime phase shifts of the SCN clock in vitro and that these treatments affect glutamate, N-methyl-D-aspartate receptor, and associated signaling processes differently. More recently we found that Cu induces mitogen-activated protein kinase-dependent phase shifts, while the mechanisms by which Cu removal induces phase shifts remain unclear. Lastly, we have found that two Cu transporters are expressed in the SCN, and that one of these transporters (ATP7A) exhibits a day/night rhythm. Our results suggest that Cu homeostasis is tightly regulated in the SCN, and that changes in Cu levels may serve as a time cue for the circadian clock. We discuss these findings in light of the existing literature and current models of multiple coupled circadian oscillators in the SCN.
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Affiliation(s)
- Yukihiro Yamada
- Department of Biochemistry & Cellular and Molecular Biology, NeuroNET Research Center, University of Tennessee, Knoxville, Tennessee
| | - Rebecca A Prosser
- Department of Biochemistry & Cellular and Molecular Biology, NeuroNET Research Center, University of Tennessee, Knoxville, Tennessee
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7
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Kardos J, Héja L, Simon Á, Jablonkai I, Kovács R, Jemnitz K. Copper signalling: causes and consequences. Cell Commun Signal 2018; 16:71. [PMID: 30348177 PMCID: PMC6198518 DOI: 10.1186/s12964-018-0277-3] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 09/24/2018] [Indexed: 12/18/2022] Open
Abstract
Copper-containing enzymes perform fundamental functions by activating dioxygen (O2) and therefore allowing chemical energy-transfer for aerobic metabolism. The copper-dependence of O2 transport, metabolism and production of signalling molecules are supported by molecular systems that regulate and preserve tightly-bound static and weakly-bound dynamic cellular copper pools. Disruption of the reducing intracellular environment, characterized by glutathione shortage and ambient Cu(II) abundance drives oxidative stress and interferes with the bidirectional, copper-dependent communication between neurons and astrocytes, eventually leading to various brain disease forms. A deeper understanding of of the regulatory effects of copper on neuro-glia coupling via polyamine metabolism may reveal novel copper signalling functions and new directions for therapeutic intervention in brain disorders associated with aberrant copper metabolism.
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Affiliation(s)
- Julianna Kardos
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok körútja 2, Budapest, 1117 Hungary
| | - László Héja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok körútja 2, Budapest, 1117 Hungary
| | - Ágnes Simon
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok körútja 2, Budapest, 1117 Hungary
| | - István Jablonkai
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok körútja 2, Budapest, 1117 Hungary
| | - Richard Kovács
- Institute of Neurophysiology, Charité-Universitätsmedizin, Berlin, Germany
| | - Katalin Jemnitz
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok körútja 2, Budapest, 1117 Hungary
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8
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Zhou Y, Xia XM, Lingle CJ. BK channel inhibition by strong extracellular acidification. eLife 2018; 7:38060. [PMID: 29963986 PMCID: PMC6054526 DOI: 10.7554/elife.38060] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 07/01/2018] [Indexed: 12/24/2022] Open
Abstract
Mammalian BK-type voltage- and Ca2+-dependent K+ channels are found in a wide range of cells and intracellular organelles. Among different loci, the composition of the extracellular microenvironment, including pH, may differ substantially. For example, it has been reported that BK channels are expressed in lysosomes with their extracellular side facing the strongly acidified lysosomal lumen (pH ~4.5). Here we show that BK activation is strongly and reversibly inhibited by extracellular H+, with its conductance-voltage relationship shifted by more than +100 mV at pHO 4. Our results reveal that this inhibition is mainly caused by H+ inhibition of BK voltage-sensor (VSD) activation through three acidic residues on the extracellular side of BK VSD. Given that these key residues (D133, D147, D153) are highly conserved among members in the voltage-dependent cation channel superfamily, the mechanism underlying BK inhibition by extracellular acidification might also be applicable to other members in the family.
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Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
| | - Xiao-Ming Xia
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, United States
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9
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10
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Swami S, Behera D, Agarwala A, Verma VP, Shrivastava R. β-Carboline–imidazopyridine hybrids: selective and sensitive optical sensors for copper and fluoride ions. NEW J CHEM 2018. [DOI: 10.1039/c8nj01851k] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two rationally designed β-carboline–imidazopyridine hybrid chromofluorescent sensors S1 and S2 have been successfully synthesized and evaluated for the selective sensing of metal ions and anions.
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Affiliation(s)
- Suman Swami
- Department of Chemistry
- Manipal University Jaipur
- VPO-Dehmi Kalan
- Teshil Sanganer
- Off Jaipur Ajmer Expressway
| | - Debasis Behera
- Department of Chemistry
- Manipal University Jaipur
- VPO-Dehmi Kalan
- Teshil Sanganer
- Off Jaipur Ajmer Expressway
| | - Arunava Agarwala
- Department of Chemistry
- Manipal University Jaipur
- VPO-Dehmi Kalan
- Teshil Sanganer
- Off Jaipur Ajmer Expressway
| | | | - Rahul Shrivastava
- Department of Chemistry
- Manipal University Jaipur
- VPO-Dehmi Kalan
- Teshil Sanganer
- Off Jaipur Ajmer Expressway
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11
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Zhou Y, Yang H, Cui J, Lingle CJ. Threading the biophysics of mammalian Slo1 channels onto structures of an invertebrate Slo1 channel. J Gen Physiol 2017; 149:985-1007. [PMID: 29025867 PMCID: PMC5677106 DOI: 10.1085/jgp.201711845] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/20/2017] [Indexed: 11/24/2022] Open
Abstract
Zhou et al. consider the biophysics of large-conductance Ca2+-activated Slo1 channels in the context of Aplysia Slo1 structures. For those interested in the machinery of ion channel gating, the Ca2+ and voltage-activated BK K+ channel provides a compelling topic for investigation, by virtue of its dual allosteric regulation by both voltage and intracellular Ca2+ and because its large-single channel conductance facilitates detailed kinetic analysis. Over the years, biophysical analyses have illuminated details of the allosteric regulation of BK channels and revealed insights into the mechanism of BK gating, e.g., inner cavity size and accessibility and voltage sensor-pore coupling. Now the publication of two structures of an Aplysia californica BK channel—one liganded and one metal free—promises to reinvigorate functional studies and interpretation of biophysical results. The new structures confirm some of the previous functional inferences but also suggest new perspectives regarding cooperativity between Ca2+-binding sites and the relationship between voltage- and Ca2+-dependent gating. Here we consider the extent to which the two structures explain previous functional data on pore-domain properties, voltage-sensor motions, and divalent cation binding and activation of the channel.
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Affiliation(s)
- Yu Zhou
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
| | - Huanghe Yang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University, St. Louis, MO
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis MO
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12
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Srivastava S, Panda S, Li Z, Fuhs SR, Hunter T, Thiele DJ, Hubbard SR, Skolnik EY. Histidine phosphorylation relieves copper inhibition in the mammalian potassium channel KCa3.1. eLife 2016; 5. [PMID: 27542194 PMCID: PMC5005030 DOI: 10.7554/elife.16093] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 08/14/2016] [Indexed: 12/02/2022] Open
Abstract
KCa2.1, KCa2.2, KCa2.3 and KCa3.1 constitute a family of mammalian small- to intermediate-conductance potassium channels that are activated by calcium-calmodulin. KCa3.1 is unique among these four channels in that activation requires, in addition to calcium, phosphorylation of a single histidine residue (His358) in the cytoplasmic region, by nucleoside diphosphate kinase-B (NDPK-B). The mechanism by which KCa3.1 is activated by histidine phosphorylation is unknown. Histidine phosphorylation is well characterized in prokaryotes but poorly understood in eukaryotes. Here, we demonstrate that phosphorylation of His358 activates KCa3.1 by antagonizing copper-mediated inhibition of the channel. Furthermore, we show that activated CD4+ T cells deficient in intracellular copper exhibit increased KCa3.1 histidine phosphorylation and channel activity, leading to increased calcium flux and cytokine production. These findings reveal a novel regulatory mechanism for a mammalian potassium channel and for T-cell activation, and highlight a unique feature of histidine versus serine/threonine and tyrosine as a regulatory phosphorylation site. DOI:http://dx.doi.org/10.7554/eLife.16093.001
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Affiliation(s)
- Shekhar Srivastava
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, United States.,Division of Nephrology, New York University School of Medicine, New York, United States.,Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University, New York, United States
| | - Saswati Panda
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, United States.,Division of Nephrology, New York University School of Medicine, New York, United States.,Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University, New York, United States
| | - Zhai Li
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, United States.,Division of Nephrology, New York University School of Medicine, New York, United States.,Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University, New York, United States
| | - Stephen R Fuhs
- Molecular and Cell Biology Laboratory, Salk Institute for Biological Studies, La Jolla, United States
| | - Tony Hunter
- Molecular and Cell Biology Laboratory, Salk Institute for Biological Studies, La Jolla, United States
| | - Dennis J Thiele
- Department of Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, United States.,Department of Biochemistry, Duke University School of Medicine, Durham, United States
| | - Stevan R Hubbard
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, United States.,Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University, New York, United States
| | - Edward Y Skolnik
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, United States.,Division of Nephrology, New York University School of Medicine, New York, United States.,Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University, New York, United States
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13
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Abstract
BK channels are universal regulators of cell excitability, given their exceptional unitary conductance selective for K(+), joint activation mechanism by membrane depolarization and intracellular [Ca(2+)] elevation, and broad expression pattern. In this chapter, we discuss the structural basis and operational principles of their activation, or gating, by membrane potential and calcium. We also discuss how the two activation mechanisms interact to culminate in channel opening. As members of the voltage-gated potassium channel superfamily, BK channels are discussed in the context of archetypal family members, in terms of similarities that help us understand their function, but also seminal structural and biophysical differences that confer unique functional properties.
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Affiliation(s)
- A Pantazis
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States
| | - R Olcese
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States.
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14
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Abstract
Hv1 is a voltage-gated proton-selective channel that plays critical parts in host defense, sperm motility, and cancer progression. Hv1 contains a conserved voltage-sensor domain (VSD) that is shared by a large family of voltage-gated ion channels, but it lacks a pore domain. Voltage sensitivity and proton conductivity are conferred by a unitary VSD that consists of four transmembrane helices. The architecture of Hv1 differs from that of cation channels that form a pore in the center among multiple subunits (as in most cation channels) or homologous repeats (as in voltage-gated sodium and calcium channels). Hv1 forms a dimer in which a cytoplasmic coiled coil underpins the two protomers and forms a single, long helix that is contiguous with S4, the transmembrane voltage-sensing segment. The closed-state structure of Hv1 was recently solved using X-ray crystallography. In this article, we discuss the gating mechanism of Hv1 and focus on cooperativity within dimers and their sensitivity to metal ions.
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Affiliation(s)
- Yasushi Okamura
- Department of Integrative Physiology, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan; , ,
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15
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Saleem M, Khang CH, Kim MH, Lee KH. Chromo/Fluorogenic Detection of Co(2+), Hg(2+) and Cu(2+) by the Simple Schiff Base Sensor. J Fluoresc 2015; 26:11-22. [PMID: 26585349 DOI: 10.1007/s10895-015-1723-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 11/10/2015] [Indexed: 01/02/2023]
Abstract
Herein, we reported the ditriazole Schiff base derivative 1 and evaluated its photophysical properties on induction of varieties of metal ions including Na(+), Ag(+), Ni(2+), Mn(2+), Pd(2+), Co(2+), Hg(2+), Cu(2+), Pb(2+), Cd(2+), Zn(2+), Sn(2+), Fe(2+), Fe(3+), Cr(3+) and Al(3+), in order to figure out its potential as ion sensor. The ligand 1 exhibited the strong colorimetric change in the reaction solution as well as absorption spectral shifting with the concomitant appearance of well-defined isosbestic points only upon Co(2+), Hg(2+) and Cu(2+) addition corroborates its applicability as multichannel ion detector. The different extent of spectral shifting as well as unique chromogenic change in the probe solution upon Co(2+), Hg(2+) and Cu(2+) introduction can be used as the discrimination tool for these metal ions. The ligand-metal binding stoichiometry was assessed by their optical response which was further supported by the FT-IR, NMR and mass spectrometric analysis. The association constant and the detection limits of the ligand toward Co(2+), Hg(2+) and Cu(2+) ions were calculated to be 1.52 × 10(-8), 3.26 × 10(-9), 1.16 × 10(-8) and 3.87 × 10(-10), 5.47 × 10(-11), 8.91 × 10(-11) M, respectively, employing the Benesi-Hilderbrand equation and 3 σ slope(-1) methods. Furthermore, the successive addition of Co(2+), Hg(2+) and Cu(2+) induce the constant decline in the fluorescence emission signal intensity of the probe. The quenching efficiency of the probe upon metallic induction was fitted to the Stern-Volmer equation which yielded the upward curvature in case of all the three metals ions (Co(2+), Hg(2+) and Cu(2+)) when (Io/I-1) was plotted against the quencher concentration indicating the occurrence of both the dynamic and static quenching process in the system with the average Stern-Volmer quenching constant values of 9.25 × 10(-7), 1.14 × 10(-7), 1.829 × 10(-7), respectively.
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Affiliation(s)
- Muhammad Saleem
- Department of Chemistry, Kongju National University, Gongju, Chungnam, 314-701, Republic of Korea
| | - Chung Ho Khang
- Department of Chemistry, Kongju National University, Gongju, Chungnam, 314-701, Republic of Korea
| | - Moon-Hwan Kim
- Biomaterial Research Center, Korea Research Institute of Chemical Technology, PO Box 107, Yuseong, Daejon, 305-600, Republic of Korea
| | - Ki Hwan Lee
- Department of Chemistry, Kongju National University, Gongju, Chungnam, 314-701, Republic of Korea.
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16
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Saleem M, Lee KH. Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species. RSC Adv 2015. [DOI: 10.1039/c5ra11388a] [Citation(s) in RCA: 157] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu2+, Fe2+/Fe3+, Zn2+and Hg2+.
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Affiliation(s)
- Muhammad Saleem
- Department of Chemistry
- Kongju National University
- Gongju
- Republic of Korea
| | - Ki Hwan Lee
- Department of Chemistry
- Kongju National University
- Gongju
- Republic of Korea
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17
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Yu W, Jiang LH, Zheng Y, Hu X, Luo J, Yang W. Inactivation of TRPM2 channels by extracellular divalent copper. PLoS One 2014; 9:e112071. [PMID: 25386648 PMCID: PMC4227687 DOI: 10.1371/journal.pone.0112071] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Accepted: 10/11/2014] [Indexed: 12/02/2022] Open
Abstract
Cu2+ is an essential metal ion that plays a critical role in the regulation of a number of ion channels and receptors in addition to acting as a cofactor in a variety of enzymes. Here, we showed that human melastatin transient receptor potential 2 (hTRPM2) channel is sensitive to inhibition by extracellular Cu2+. Cu2+ at concentrations as low as 3 µM inhibited the hTRPM2 channel completely and irreversibly upon washing or using Cu2+ chelators, suggesting channel inactivation. The Cu2+-induced inactivation was similar when the channels conducted inward or outward currents, indicating the permeating ions had little effect on Cu2+-induced inactivation. Furthermore, Cu2+ had no effect on singe channel conductance. Alanine substitution by site-directed mutagenesis of His995 in the pore-forming region strongly attenuated Cu2+-induced channel inactivation, and mutation of several other pore residues to alanine altered the kinetics of channel inactivation by Cu2+. In addition, while introduction of the P1018L mutation is known to result in channel inactivation, exposure to Cu2+ accelerated the inactivation of this mutant channel. In contrast with the hTRPM2, the mouse TRPM2 (mTRPM2) channel, which contains glutamine at the position equivalent to His995, was insensitive to Cu2+. Replacement of His995 with glutamine in the hTRPM2 conferred loss of Cu2+-induced channel inactivation. Taken together, these results suggest that Cu2+ inactivates the hTRPM2 channel by interacting with the outer pore region. Our results also indicate that the amino acid residue difference in this region gives rise to species-dependent effect by Cu2+ on the human and mouse TRPM2 channels.
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Affiliation(s)
- Wenyue Yu
- Key Laboratory of Medical Neurobiology of the Ministry of Health of China, Zhejiang Province Key Laboratory of Neurobiology, Department of Neurobiology, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Lin-Hua Jiang
- Department of Physiology and Neurobiology, Xinxiang Medical University, Xinxiang, Henan Province, China
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Yang Zheng
- Key Laboratory of Medical Neurobiology of the Ministry of Health of China, Zhejiang Province Key Laboratory of Neurobiology, Department of Neurobiology, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Xupang Hu
- Key Laboratory of Medical Neurobiology of the Ministry of Health of China, Zhejiang Province Key Laboratory of Neurobiology, Department of Neurobiology, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Jianhong Luo
- Key Laboratory of Medical Neurobiology of the Ministry of Health of China, Zhejiang Province Key Laboratory of Neurobiology, Department of Neurobiology, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
- * E-mail: (JHL); (WY)
| | - Wei Yang
- Key Laboratory of Medical Neurobiology of the Ministry of Health of China, Zhejiang Province Key Laboratory of Neurobiology, Department of Neurobiology, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, China
- * E-mail: (JHL); (WY)
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18
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Marchetti C. Interaction of metal ions with neurotransmitter receptors and potential role in neurodiseases. Biometals 2014; 27:1097-113. [PMID: 25224737 DOI: 10.1007/s10534-014-9791-y] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 09/05/2014] [Indexed: 12/25/2022]
Abstract
There is increasing evidence that toxic metals play a role in diseases of unknown etiology. Their action is often mediated by membrane proteins, and in particular neurotransmitter receptors. This brief review will describe recent findings on the direct interaction of metal ions with ionotropic γ-aminobutyric acid (GABAA) and glutamate receptors, the main inhibitory and excitatory neurotransmitter receptors in the mammalian central nervous system, respectively. Both hyper and hypo function of these receptors are involved in neurological and psychotic syndromes and modulation by metal ions is an important pharmacological issue. The focus will be on three xenobiotic metals, lead (Pb), cadmium (Cd) and nickel (Ni) that have no biological function and whose presence in living organisms is only detrimental, and two trace metals, zinc (Zn) and copper (Cu), which are essential for several enzymatic functions, but can mediate toxic actions if deregulated. Despite limited access to the brain and tight control by metalloproteins, exogenous metals interfere with receptor performances by mimicking physiological ions and occupying one or more modulatory sites on the protein. These interactions will be discussed as a potential cause of neuronal dysfunction.
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Affiliation(s)
- Carla Marchetti
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, via De Marini, 6, 16149, Genoa, Italy,
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19
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Abstract
Inhibition of GABAA receptors by Cu(2+) has been appreciated for some time, but differences between synaptic and extrasynaptic GABAA receptors have not been explored. We show that Cu(2+) potently blocks steady-state GABA currents mediated by extrasynaptic δ subunit-containing GABAA receptors (δ-GABAARs) with an IC50 of 65 nM. This compares with an IC50 of 85 μM for synaptic γ subunit-containing GABAARs (γ-GABAARs). To test the significance of this subunit selectivity, we examined the blocking action of Cu(2+) on neurons of the mouse cerebellum and striatum, brain regions that are known to express both types of receptor. Cu(2+) was shown to significantly reduce tonic inhibition mediated by extrasynaptic δ-GABAARs with little action on phasic inhibition mediated by conventional synaptic γ-GABAARs. We speculate on the implications of these observations for conditions, such as Wilson's disease, that can involve raised Cu(2+) levels in the brain.
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20
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Niu X, Liu G, Wu RS, Chudasama N, Zakharov SI, Karlin A, Marx SO. Orientations and proximities of the extracellular ends of transmembrane helices S0 and S4 in open and closed BK potassium channels. PLoS One 2013; 8:e58335. [PMID: 23472181 PMCID: PMC3589268 DOI: 10.1371/journal.pone.0058335] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Accepted: 02/02/2013] [Indexed: 11/19/2022] Open
Abstract
The large-conductance potassium channel (BK) α subunit contains a transmembrane (TM) helix S0 preceding the canonical TM helices S1 through S6. S0 lies between S4 and the TM2 helix of the regulatory β1 subunit. Pairs of Cys were substituted in the first helical turns in the membrane of BK α S0 and S4 and in β1 TM2. One such pair, W22C in S0 and W203C in S4, was 95% crosslinked endogenously. Under voltage-clamp conditions in outside-out patches, this crosslink was reduced by DTT and reoxidized by a membrane-impermeant bis-quaternary ammonium derivative of diamide. The rate constants for this reoxidation were not significantly different in the open and closed states of the channel. Thus, these two residues are approximately equally close in the two states. In addition, 90% crosslinking of a second pair, R20C in S0 and W203C in S4, had no effect on the V50 for opening. Taken together, these findings indicate that separation between residues at the extracellular ends of S0 and S4 is not required for voltage-sensor activation. On the contrary, even though W22C and W203C were equally likely to form a disulfide in the activated and deactivated states, relative immobilization by crosslinking of these two residues favored the activated state. Furthermore, the efficiency of recrosslinking of W22C and W203C on the cell surface was greater in the presence of the β1 subunit than in its absence, consistent with β1 acting through S0 to stabilize its immobilization relative to α S4.
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Affiliation(s)
- Xiaowei Niu
- From the Center for Molecular Recognition, Departments of Biochemistry, Physiology, and Neurology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Guoxia Liu
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Roland S. Wu
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Neelesh Chudasama
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Sergey I. Zakharov
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
| | - Arthur Karlin
- From the Center for Molecular Recognition, Departments of Biochemistry, Physiology, and Neurology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- * E-mail: (AK); (SOM)
| | - Steven O. Marx
- Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
- * E-mail: (AK); (SOM)
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21
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Tamba BI, Leon MM, Petreus T. Common trace elements alleviate pain in an experimental mouse model. J Neurosci Res 2013; 91:554-61. [PMID: 23362003 DOI: 10.1002/jnr.23191] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 11/25/2012] [Indexed: 11/10/2022]
Abstract
Trace elements represent a group of essential metals or metaloids necessary for life, present in minute amounts. Analgesic adjuvants can enhance the effect of other pain drugs or be used for pain control themselves. Previous studies on the effects of trace elements on nociception and their potential use as analgesic adjuvants have yielded conflicting results. In this study, we tested the hypothesis that three vital trace elements (Zn²⁺, Mg²⁺, Cu²⁺) have direct antinociceptive effects. Groups of eight Swiss mice were intraperitoneally (i.p) injected with incremental concentrations of Zn²⁺ sulfate (0.5, 2.0 mg/kg), Zn²⁺ citrate (0.125, 0.5 mg/kg), Mg²⁺ chloride (37.5, 75, 150 mg/kg), Cu²⁺ chloride (0.5, 1.0, 2.0 mg/kg), and Cu²⁺ sulfate (0.5, 1.0 mg/kg) or saline (control). Evaluations were made by hot plate (HP) and tail flick (TF) tests for central antinociceptive effect, writhing test (WT) for visceral antinociceptive effect, and activity cage (AC) test for spontaneous behavior. Zn²⁺ induced pain inhibition in HP/TF tests (up to 17%) and WT (up to 25%), with no significant differences among the salts used. Mg²⁺ salts induced pain inhibition for all performed tests (up to 85% in WT). Cu²⁺ salts showed antinociceptive effects for HP/TF (up to 28.6%) and WT (57.28%). Only Mg²⁺ and Cu²⁺ salts have displayed significant effects in AC (Mg²⁺ anxiolytic/depressant effect; Cu²⁺ anxiolytic effect). We interpret these data to mean that all tested trace elements induced antinociceptive effects in central and visceral pain tests. Our data indicate the potential use of these cheap adjuvants in pain therapy.
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Affiliation(s)
- Bogdan I Tamba
- Centre for the Study and Therapy of Pain, Gr. T. Popa University of Medicine and Pharmacy, Iasi, Romania.
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22
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Nguyen NV, Gruslova A, Kosiba WA, Wang B. Combined single-channel and macroscopic recording techniques to analyze gating mechanisms of the large conductance Ca2+ and voltage activated (BK) potassium channel. Methods Mol Biol 2013; 998:133-47. [PMID: 23529426 DOI: 10.1007/978-1-62703-351-0_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Ion channels are integral membrane proteins that regulate membrane potentials and signaling of cells in response to various stimuli. The patch-clamp technique enables the study of single channels or a population of channels. The macroscopic recording approaches are powerful in revealing population-averaged behaviors of channels both under basal conditions and in response to various stimuli, modulators and drugs. On their own, however, these approaches can be insufficient for determinations of channel gating mechanisms as they do not accurately report channel open probabilities below 10(-2) to 10(-3). This obstacle can be overcome with the use of single-channel recording techniques. Single-channel recording techniques can be applied to one or a few channels to estimate P o over a larger range than macroscopic recordings. The combination of heterologous overexpression of ion channels with macroscopic and single-channel recordings can be applied to hundreds of channels to estimate P o between 1 and 10(-8). Here, we describe practical approaches of single-channel recordings that our laboratory utilizes. We also provide examples where the combined macroscopic and single channel approach can be employed to study gating mechanisms of the BK type, large conductance, Ca(2+) and voltage activated potassium channel in a mammalian expression system. The techniques presented should be generally applicable to the studies of ion channels in heterologous expression systems.
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Affiliation(s)
- Nguyen V Nguyen
- Department of Radiology, University of Miami School of Medicine, Miami, FL, USA
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23
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Shcheglovitov A, Vitko I, Lazarenko RM, Orestes P, Todorovic SM, Perez-Reyes E. Molecular and biophysical basis of glutamate and trace metal modulation of voltage-gated Ca(v)2.3 calcium channels. ACTA ACUST UNITED AC 2012; 139:219-34. [PMID: 22371363 PMCID: PMC3289959 DOI: 10.1085/jgp.201110699] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Here, we describe a new mechanism by which glutamate (Glu) and trace metals reciprocally modulate activity of the Cav2.3 channel by profoundly shifting its voltage-dependent gating. We show that zinc and copper, at physiologically relevant concentrations, occupy an extracellular binding site on the surface of Cav2.3 and hold the threshold for activation of these channels in a depolarized voltage range. Abolishing this binding by chelation or the substitution of key amino acid residues in IS1–IS2 (H111) and IS2–IS3 (H179 and H183) loops potentiates Cav2.3 by shifting the voltage dependence of activation toward more negative membrane potentials. We demonstrate that copper regulates the voltage dependence of Cav2.3 by affecting gating charge movements. Thus, in the presence of copper, gating charges transition into the “ON” position slower, delaying activation and reducing the voltage sensitivity of the channel. Overall, our results suggest a new mechanism by which Glu and trace metals transiently modulate voltage-dependent gating of Cav2.3, potentially affecting synaptic transmission and plasticity in the brain.
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24
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Labeling of specific cysteines in proteins using reversible metal protection. Biophys J 2011; 100:2513-21. [PMID: 21575586 DOI: 10.1016/j.bpj.2011.03.063] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 02/14/2011] [Accepted: 03/29/2011] [Indexed: 02/05/2023] Open
Abstract
Fluorescence spectroscopy is an indispensible tool for studying the structure and conformational dynamics of protein molecules both in isolation and in their cellular context. The ideal probes for monitoring intramolecular protein motions are small, cysteine-reactive fluorophores. However, it can be difficult to obtain specific labeling of a desired cysteine in proteins with multiple cysteines, in a mixture of proteins, or in a protein's native environment, in which many cysteine-containing proteins are present. To obtain specific labeling, we developed a method we call cysteine metal protection and labeling (CyMPL). With this method, a desired cysteine can be reversibly protected by binding group 12 metal ions (e.g., Cd²⁺ and Zn²⁺) while background cysteines are blocked with nonfluorescent covalent modifiers. We increased the metal affinity for specific cysteines by incorporating them into minimal binding sites in existing secondary structural motifs (i.e., α-helix or β-strand). After the metal ions were removed, the deprotected cysteines were then available to specifically react with a fluorophore.
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25
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Dharia S, Rabbitt RD. Monitoring voltage-dependent charge displacement of Shaker B-IR K+ ion channels using radio frequency interrogation. PLoS One 2011; 6:e17363. [PMID: 21387000 PMCID: PMC3046147 DOI: 10.1371/journal.pone.0017363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Accepted: 02/01/2011] [Indexed: 11/18/2022] Open
Abstract
Here we introduce a new technique that probes voltage-dependent charge displacements of excitable membrane-bound proteins using extracellularly applied radio frequency (RF, 500 kHz) electric fields. Xenopus oocytes were used as a model cell for these experiments, and were injected with cRNA encoding Shaker B-IR (ShB-IR) K(+) ion channels to express large densities of this protein in the oocyte membranes. Two-electrode voltage clamp (TEVC) was applied to command whole-cell membrane potential and to measure channel-dependent membrane currents. Simultaneously, RF electric fields were applied to perturb the membrane potential about the TEVC level and to measure voltage-dependent RF displacement currents. ShB-IR expressing oocytes showed significantly larger changes in RF displacement currents upon membrane depolarization than control oocytes. Voltage-dependent changes in RF displacement currents further increased in ShB-IR expressing oocytes after ∼120 µM Cu(2+) addition to the external bath. Cu(2+) is known to bind to the ShB-IR ion channel and inhibit Shaker K(+) conductance, indicating that changes in the RF displacement current reported here were associated with RF vibration of the Cu(2+)-linked mobile domain of the ShB-IR protein. Results demonstrate the use of extracellular RF electrodes to interrogate voltage-dependent movement of charged mobile protein domains--capabilities that might enable detection of small changes in charge distribution associated with integral membrane protein conformation and/or drug-protein interactions.
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Affiliation(s)
- Sameera Dharia
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America.
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26
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Wang D, Schreurs BG. Dietary cholesterol modulates the excitability of rabbit hippocampal CA1 pyramidal neurons. Neurosci Lett 2010; 479:327-31. [PMID: 20639007 DOI: 10.1016/j.neulet.2010.05.090] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 05/05/2010] [Accepted: 05/30/2010] [Indexed: 11/29/2022]
Abstract
Previous work has shown high dietary cholesterol can affect learning and memory including rabbit eyeblink conditioning and this effect may be due to increased membrane cholesterol and enhanced hippocampal amyloid beta production. This study investigated whether dietary cholesterol modulates rabbit hippocampal CA1 neuron membrane properties known to be involved in rabbit eyeblink conditioning. Whole-cell current clamp recordings in hippocampal neurons from rabbits fed 2 percent cholesterol or normal chow for 8 weeks revealed changes including decreased after-hyperpolarization amplitudes (AHPs) - an index of membrane excitability shown to be important for rabbit eyeblink conditioning. This index was reversed by adding copper to drinking water - a dietary manipulation that can retard rabbit eyeblink conditioning. Evidence of cholesterol effects on membrane excitability was provided by application of methyl-beta-cyclodextrin, a compound that reduces membrane cholesterol, which increased the excitability of hippocampal CA1 neurons.
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Affiliation(s)
- Desheng Wang
- Department of Physiology and Pharmacology, West Virginia University School of Medicine, Morgantown, WV 26506, United States.
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27
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Hou S, Vigeland LE, Zhang G, Xu R, Li M, Heinemann SH, Hoshi T. Zn2+ activates large conductance Ca2+-activated K+ channel via an intracellular domain. J Biol Chem 2009; 285:6434-42. [PMID: 20037152 DOI: 10.1074/jbc.m109.069211] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Zinc is an essential trace element and plays crucial roles in normal development, often as an integral structural component of transcription factors and enzymes. Recent evidence suggests that intracellular Zn(2+) functions as a signaling molecule, mediating a variety of important physiological phenomena. However, the immediate effectors of intracellular Zn(2+) signaling are not well known. We show here that intracellular Zn(2+) potently and reversibly activates large-conductance voltage- and Ca(2+)-activated Slo1 K(+) (BK) channels. The full effect of Zn(2+) requires His(365) in the RCK1 (regulator of conductance for K(+)) domain of the channel. Furthermore, mutation of two nearby acidic residues, Asp(367) and Glu(399), also reduced activation of the channel by Zn(2+), suggesting a possible structural arrangement for Zn(2+) binding by the aforementioned residues. Extracellular Zn(2+) activated Slo1 BK channels when coexpressed with Zn(2+)-permeable TRPM7 (transient receptor potential melastatin 7) channels. The results thus demonstrate that Slo1 BK channels represent a positive and direct effector of Zn(2+) signaling and may participate in sculpting cellular response to an increase in intracellular Zn(2+) concentration.
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Affiliation(s)
- Shangwei Hou
- Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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28
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Kang HW, Vitko I, Lee SS, Perez-Reyes E, Lee JH. Structural determinants of the high affinity extracellular zinc binding site on Cav3.2 T-type calcium channels. J Biol Chem 2009; 285:3271-81. [PMID: 19940152 DOI: 10.1074/jbc.m109.067660] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ca(v)3.2 T-type channels contain a high affinity metal binding site for trace metals such as copper and zinc. This site is occupied at physiologically relevant concentrations of these metals, leading to decreased channel activity and pain transmission. A histidine at position 191 was recently identified as a critical determinant for both trace metal block of Ca(v)3.2 and modulation by redox agents. His(191) is found on the extracellular face of the Ca(v)3.2 channel on the IS3-S4 linker and is not conserved in other Ca(v)3 channels. Mutation of the corresponding residue in Ca(v)3.1 to histidine, Gln(172), significantly enhances trace metal inhibition, but not to the level observed in wild-type Ca(v)3.2, implying that other residues also contribute to the metal binding site. The goal of the present study is to identify these other residues using a series of chimeric channels. The key findings of the study are that the metal binding site is composed of a Asp-Gly-His motif in IS3-S4 and a second aspartate residue in IS2. These results suggest that metal binding stabilizes the closed conformation of the voltage-sensor paddle in repeat I, and thereby inhibits channel opening. These studies provide insight into the structure of T-type channels, and identify an extracellular motif that could be targeted for drug development.
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Affiliation(s)
- Ho-Won Kang
- Department of Life Science, Sogang University, Seoul 121-742, Korea
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29
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Zhang X, Bursulaya B, Lee CC, Chen B, Pivaroff K, Jegla T. Divalent cations slow activation of EAG family K+ channels through direct binding to S4. Biophys J 2009; 97:110-20. [PMID: 19580749 DOI: 10.1016/j.bpj.2009.04.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Revised: 04/14/2009] [Accepted: 04/15/2009] [Indexed: 10/20/2022] Open
Abstract
Voltage-gated K+ channels share a common voltage sensor domain (VSD) consisting of four transmembrane helices, including a highly mobile S4 helix that contains the major gating charges. Activation of ether-a-go-go (EAG) family K+ channels is sensitive to external divalent cations. We show here that divalent cations slow the activation rate of two EAG family channels (Kv12.1 and Kv10.2) by forming a bridge between a residue in the S4 helix and acidic residues in S2. Histidine 328 in the S4 of Kv12.1 favors binding of Zn2+ and Cd2+, whereas the homologous residue Serine 321 in Kv10.2 contributes to effects of Mg2+ and Ni2+. This novel finding provides structural constraints for the position of transmembrane VSD helices in closed, ion-bound EAG family channels. Homology models of Kv12.1 and Kv10.2 VSD structures based on a closed-state model of the Shaker family K+ channel Kv1.2 match these constraints. Our results suggest close conformational conservation between closed EAG and Shaker family channels, despite large differences in voltage sensitivity, activation rates, and activation thresholds.
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Affiliation(s)
- Xiaofei Zhang
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California 92037, USA
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Unnerståle S, Lind J, Papadopoulos E, Mäler L. Solution structure of the HsapBK K+ channel voltage-sensor paddle sequence. Biochemistry 2009; 48:5813-21. [PMID: 19456106 DOI: 10.1021/bi9004599] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Voltage-gated potassium channels open and close in response to changes in the membrane potential. In this study, we have determined the NMR solution structure of the putative S3b-S4 voltage-sensor paddle fragment, the part that moves to mediate voltage gating, of the HsapBK potassium channel in dodecylphosphocholine (DPC) micelles. This paper presents the first structure of the S3b-S4 fragment from a BK channel. Diffusion coefficients as determined from PFG NMR experiments showed that a well-defined complex between the peptide and DPC molecules was formed. The structure reveals a helix-turn-helix motif, which is in agreement with crystal structures of other voltage-gated potassium channels, thus indicating that it is feasible to study the isolated fragment. The paddle motifs generally contain several basic residues, implicated in the gating. The critical Arg residues in this structure all reside on the surface, which is in agreement with crystal structures of K(v) channels. Similarities in the structure of the S3b-S4 fragment in BK and K(v) channels as well as important differences are seen, which may be important for explaining the details in paddle movement within a bilayer.
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Affiliation(s)
- Sofia Unnerståle
- Department of Biochemistry and Biophysics, Center for Biomembrane Research, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
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31
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Ridgway LD, Kim EY, Dryer SE. MAGI-1 interacts with Slo1 channel proteins and suppresses Slo1 expression on the cell surface. Am J Physiol Cell Physiol 2009; 297:C55-65. [PMID: 19403801 DOI: 10.1152/ajpcell.00073.2009] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large conductance Ca(2+)-activated K(+) (BK(Ca)) channels encoded by the Slo1 gene (also known as KCNMA1) are physiologically important in a wide range of cell types and form complexes with a number of other proteins that affect their function. We performed a yeast two-hybrid screen to identify proteins that interact with BK(Ca) channels using a bait construct derived from domains in the extreme COOH-terminus of Slo1. A protein known as membrane-associated guanylate kinase with inverted orientation protein-1 (MAGI-1) was identified in this screen. MAGI-1 is a scaffolding protein that allows formation of complexes between certain transmembrane proteins, actin-binding proteins, and other regulatory proteins. MAGI-1 is expressed in a number of tissues, including podocytes and the brain. The interaction between MAGI-1 and BK(Ca) channels was confirmed by coimmunoprecipitation and glutathione S-transferase pull-down assays in differentiated cells of a podocyte cell line and in human embryonic kidneys (HEK)293T cells transiently coexpressing MAGI-1a and three different COOH-terminal Slo1 variants. Coexpression of MAGI-1 with Slo1 channels in HEK-293T cells results in a significant reduction in the surface expression of Slo1, as assessed by cell-surface biotinylation assays, confocal microscopy, and whole cell recordings. Partial knockdown of endogenous MAGI-1 expression by small interfering RNA (siRNA) in differentiated podocytes increased the surface expression of endogenous Slo1 as assessed by electrophysiology and cell-surface biotinylation assays, whereas overexpression of MAGI-1a reduced steady-state voltage-evoked outward current through podocyte BK(Ca) channels. These data suggest that MAGI-1 plays a role in regulation of surface expression of BK(Ca) channels in the kidney and possibly in other tissues.
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Affiliation(s)
- Lon D Ridgway
- Dept. of Biology and Biochemistry, Univ. of Houston, Houston, TX 77204-5001, USA
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32
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Bousquet-Moore D, Ma XM, Nillni EA, Czyzyk TA, Pintar JE, Eipper BA, Mains RE. Reversal of physiological deficits caused by diminished levels of peptidylglycine alpha-amidating monooxygenase by dietary copper. Endocrinology 2009; 150:1739-47. [PMID: 19022883 PMCID: PMC2659272 DOI: 10.1210/en.2008-1202] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Amidated peptides are critically involved in many physiological functions. Genetic deletion of peptidylglycine alpha-amidating monooxygenase (PAM), the only enzyme that can synthesize these peptides, is embryonically lethal. The goal of the present study was the identification of physiological functions impaired by haploinsufficiency of PAM. Regulation of the hypothalamic-pituitary-thyroid axis and body temperature, functions requiring contributions from multiple amidated peptides, were selected for evaluation. Based on serum T(4) and pituitary TSH-beta mRNA levels, mice heterozygous for PAM (PAM(+/-)) were euthyroid at baseline. Feedback within the hypothalamic-pituitary-thyroid axis was impaired in PAM(+/-) mice made hypothyroid using a low iodine/propylthiouracil diet. Despite their normal endocrine response to cold, PAM(+/-) mice were unable to maintain body temperature as well as wild-type littermates when kept in a 4 C environment. When provided with additional dietary copper, PAM(+/-) mice maintained body temperature as well as wild-type mice. Pharmacological activation of vasoconstriction or shivering also allowed PAM(+/-) mice to maintain body temperature. Cold-induced vasoconstriction was deficient in PAM(+/-) mice. This deficit was eliminated in PAM(+/-) mice receiving a diet with supplemental copper. These results suggest that dietary deficiency of copper, coupled with genetic deficits in PAM, could result in physiological deficits in humans.
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Affiliation(s)
- D Bousquet-Moore
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030-3401, USA
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