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Charge Transport by Light-Activated Rhodopsins Determined by Electrophysiological Recordings. Methods Mol Biol 2020. [PMID: 32865739 DOI: 10.1007/978-1-0716-0830-2_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Electrophysiological experiments are required to determine the ion transport properties of light-activated currents from microbial rhodopsin expressing cells. The recordings set the quantitative basis for correlation with spectroscopic data and for understanding of channel gating, ion transport vectoriality, or ion selectivity. This chapter focuses on voltage-clamp recordings of channelrhodopsin-2-expressing cells, and it will describe different illumination protocols that reveal the kinetic properties of gating. While the opening and closing reaction is determined from a single turnover upon a short laser flash, desensitization of the light-gated currents is studied under continuous illumination. Recovery from the desensitized state is probed after prolonged illumination with a subsequent light activation upon different dark intervals. Compiling the experimental data will define a minimum number of states in kinetic schemes used to describe the light-gated currents in channelrhodopsins, and emphasis will be given on how to correlate the results with the different time-resolved spectroscopic experiments.
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Abstract
In this study the laws of mechanics for multi-component systems are used to develop a theory for the diffusion of ions in the presence of an electrostatic field. The analysis begins with the governing equation for the species velocity and it leads to the governing equation for the species diffusion velocity. Simplification of this latter result provides a momentum equation containing three dominant forces: (a) the gradient of the partial pressure, (b) the electrostatic force, and (c) the diffusive drag force that is a central feature of the Maxwell-Stefan equations. For ideal gas mixtures we derive the classic Nernst-Planck equation. For liquid-phase diffusion we encounter a situation in which the Nernst-Planck contribution to diffusion differs by several orders of magnitude from that obtained for ideal gases.
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Hansen UP, Rauh O, Schroeder I. A simple recipe for setting up the flux equations of cyclic and linear reaction schemes of ion transport with a high number of states: The arrow scheme. Channels (Austin) 2015; 10:119-38. [PMID: 26646356 DOI: 10.1080/19336950.2015.1120391] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
The calculation of flux equations or current-voltage relationships in reaction kinetic models with a high number of states can be very cumbersome. Here, a recipe based on an arrow scheme is presented, which yields a straightforward access to the minimum form of the flux equations and the occupation probability of the involved states in cyclic and linear reaction schemes. This is extremely simple for cyclic schemes without branches. If branches are involved, the effort of setting up the equations is a little bit higher. However, also here a straightforward recipe making use of so-called reserve factors is provided for implementing the branches into the cyclic scheme, thus enabling also a simple treatment of such cases.
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Affiliation(s)
- Ulf-Peter Hansen
- a Department of Structural Biology , University of Kiel , Kiel , Germany
| | - Oliver Rauh
- b Plant Membrane Biophysics , Technical University of Darmstadt , Darmstadt , Germany
| | - Indra Schroeder
- b Plant Membrane Biophysics , Technical University of Darmstadt , Darmstadt , Germany
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Lee KA, Lee SS, Kim SY, Choi AR, Lee JH, Jung KH. Mistic-fused expression of algal rhodopsins in Escherichia coli and its photochemical properties. Biochim Biophys Acta Gen Subj 2015; 1850:1694-703. [PMID: 25869488 DOI: 10.1016/j.bbagen.2015.04.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 03/10/2015] [Accepted: 04/03/2015] [Indexed: 01/29/2023]
Abstract
BACKGROUND Since algal rhodopsins, the eukaryotic seven-transmembrane proteins, are generally difficult to express in Escherichia coli, eukaryotic cells have been used for heterologous expression. Mistic, a membrane-associated protein that was originally discovered in Bacillus subtilis, has been shown to improve the expression levels of many foreign integral membrane proteins in E. coli when used as a fusion partner linked to the N-terminus of cargo proteins. METHODS Here, we expressed two algal rhodopsins with N- and C-terminal Mistic domains in E. coli-Acetabularia rhodopsin I (ARI) and Chlamydomonas sensory rhodopsin B (CSRB, channel rhodopsin 2). UV/VIS spectroscopy, pH titration of proton acceptor residue, laser-induced photolysis and electrophysiological measurement were used for investigating important residues in proton transport and spectroscopic characters of the proteins. RESULTS Protein yield of two algal rhodopsins was enhanced, obtaining 0.12mg of Mistic-ARI and 0.04mg of Mistic-CSRB per liter of culture. Spheroplast expression Mistic-ARI had outward proton-pumping activity, indicating protein functionality. Asp89 of ARI changed its protonation state by light absorption, and Asp100 was important for O(600) formation. Electrophysiology revealed that both residues took part in proton transport. The spectroscopic analyses of Mistic-CSRB revealed its characteristics. CONCLUSIONS Fusion to the membrane-integrating protein Mistic can enhance overexpression of eukaryotic type I rhodopsins in E. coli. GENERAL SIGNIFICANCE These findings indicate that Mistic fusion and E. coli expression method could be an effective, low cost technique for studying eukaryotic membrane proteins. This may have useful implications, for example, in studying structural characteristics and optogenetics for rhodopsins.
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Affiliation(s)
- Keon Ah Lee
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea
| | - Sang-Soo Lee
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea
| | - So Young Kim
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea
| | - Ah Reum Choi
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea
| | - Jung-Ha Lee
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea
| | - Kwang-Hwan Jung
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Republic of Korea.
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Hou JH, Venkatachalam V, Cohen AE. Temporal dynamics of microbial rhodopsin fluorescence reports absolute membrane voltage. Biophys J 2014; 106:639-48. [PMID: 24507604 DOI: 10.1016/j.bpj.2013.11.4493] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/26/2013] [Accepted: 11/27/2013] [Indexed: 01/07/2023] Open
Abstract
Plasma membrane voltage is a fundamentally important property of a living cell; its value is tightly coupled to membrane transport, the dynamics of transmembrane proteins, and to intercellular communication. Accurate measurement of the membrane voltage could elucidate subtle changes in cellular physiology, but existing genetically encoded fluorescent voltage reporters are better at reporting relative changes than absolute numbers. We developed an Archaerhodopsin-based fluorescent voltage sensor whose time-domain response to a stepwise change in illumination encodes the absolute membrane voltage. We validated this sensor in human embryonic kidney cells. Measurements were robust to variation in imaging parameters and in gene expression levels, and reported voltage with an absolute accuracy of 10 mV. With further improvements in membrane trafficking and signal amplitude, time-domain encoding of absolute voltage could be applied to investigate many important and previously intractable bioelectric phenomena.
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Affiliation(s)
- Jennifer H Hou
- Department of Physics, Harvard University, Cambridge, Massachusetts
| | | | - Adam E Cohen
- Department of Physics, Harvard University, Cambridge, Massachusetts; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts.
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Geibel S, Lörinczi È, Bamberg E, Friedrich T. Voltage dependence of proton pumping by bacteriorhodopsin mutants with altered lifetime of the M intermediate. PLoS One 2013; 8:e73338. [PMID: 24019918 PMCID: PMC3760879 DOI: 10.1371/journal.pone.0073338] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 07/29/2013] [Indexed: 11/19/2022] Open
Abstract
The light-driven proton pump bacteriorhodopsin (BR) from Halobacterium salinarum is tightly regulated by the [H(+)] gradient and transmembrane potential. BR exhibits optoelectric properties, since spectral changes during the photocycle are kinetically controlled by voltage, which predestines BR for optical storage or processing devices. BR mutants with prolonged lifetime of the blue-shifted M intermediate would be advantageous, but the optoelectric properties of such mutants are still elusive. Using expression in Xenopus oocytes and two-electrode voltage-clamping, we analyzed photocurrents of BR mutants with kinetically destabilized (F171C, F219L) or stabilized (D96N, D96G) M intermediate in response to green light (to probe H(+) pumping) and blue laser flashes (to probe accumulation/decay of M). These mutants have divergent M lifetimes. As for BR-WT, this strictly correlates with the voltage dependence of H(+) pumping. BR-F171C and BR-F219L showed photocurrents similar to BR-WT. Yet, BR-F171C showed a weaker voltage dependence of proton pumping. For both mutants, blue laser flashes applied during and after green-light illumination showed reduced M accumulation and shorter M lifetime. In contrast, BR-D96G and BR-D96N exhibited small photocurrents, with nonlinear current-voltage curves, which increased strongly in the presence of azide. Blue laser flashes showed heavy M accumulation and prolonged M lifetime, which accounts for the strongly reduced H(+) pumping rate. Hyperpolarizing potentials augmented these effects. The combination of M-stabilizing and -destabilizing mutations in BR-D96G/F171C/F219L (BR-tri) shows that disruption of the primary proton donor Asp-96 is fatal for BR as a proton pump. Mechanistically, M destabilizing mutations cannot compensate for the disruption of Asp-96. Accordingly, BR-tri and BR-D96G photocurrents were similar. However, BR-tri showed negative blue laser flash-induced currents even without actinic green light, indicating that Schiff base deprotonation in BR-tri exists in the dark, in line with previous spectroscopic investigations. Thus, M-stabilizing mutations, including the triple mutation, drastically interfere with electrochemical H(+) gradient generation.
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Affiliation(s)
- Sven Geibel
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry, Frankfurt am Main, Germany
| | - Èva Lörinczi
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry, Frankfurt am Main, Germany
| | - Ernst Bamberg
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry, Frankfurt am Main, Germany
| | - Thomas Friedrich
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry, Frankfurt am Main, Germany
- Technical University of Berlin, Institute of Chemistry, Berlin, Germany
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Gradmann D, Berndt A, Schneider F, Hegemann P. Rectification of the channelrhodopsin early conductance. Biophys J 2011; 101:1057-68. [PMID: 21889442 DOI: 10.1016/j.bpj.2011.07.040] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/25/2011] [Accepted: 07/28/2011] [Indexed: 11/15/2022] Open
Abstract
We analyzed the nonlinear current-voltage relationships of the early conducting state of channelrhodopsin-2 expressed in Xenopus oocytes and human embryonic kidney cells with respect to changes of the electrochemical gradients of H(+), Na(+)/K(+), and Ca(2+)/Mg(2+). Several models were tested for wild-type ChR2 and mutations at positions E90, E123, H134, and T159. Voltage-gating was excluded as cause for the nonlinearity. However, a general enzyme kinetic model with one predominant binding site yielded good fits throughout. The empty site with an apparent charge number of about -0.3 and strong external cation binding causes some inward rectification of the uniport function. Additional inward rectification is due to asymmetric competition from outside between the transported ion species. Significant improvement of the fits was achieved by introducing an elastic voltage-divider formed by the voltage-sensitive barriers.
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Kikukawa T, Shimono K, Tamogami J, Miyauchi S, Kim SY, Kimura-Someya T, Shirouzu M, Jung KH, Yokoyama S, Kamo N. Photochemistry of Acetabularia Rhodopsin II from a Marine Plant, Acetabularia acetabulum. Biochemistry 2011; 50:8888-98. [DOI: 10.1021/bi2009932] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Takashi Kikukawa
- Faculty of Life Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Kazumi Shimono
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Jun Tamogami
- Faculty of Life Science, Hokkaido University, Sapporo 060-0810, Japan
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Seiji Miyauchi
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
- Graduate School of Pharmaceutical
Sciences, Toho University, Funabashi, Chiba
274-8510, Japan
| | - So Young Kim
- Department
of Life Science and
Institute of Biological Interfaces, Sogang University, Seoul 121-742, Korea
| | | | - Mikako Shirouzu
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan
| | - Kwang-Hwan Jung
- Department
of Life Science and
Institute of Biological Interfaces, Sogang University, Seoul 121-742, Korea
| | - Shigeyuki Yokoyama
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan
- Department
of Biophysics and Biochemistry,
Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
| | - Naoki Kamo
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
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del Rosario RCH, Oppawsky C, Tittor J, Oesterhelt D. Modeling the membrane potential generation of bacteriorhodopsin. Math Biosci 2010; 225:68-80. [PMID: 20188746 DOI: 10.1016/j.mbs.2010.02.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Revised: 02/10/2010] [Accepted: 02/13/2010] [Indexed: 10/19/2022]
Abstract
The archaeon Halobacterium salinarum can grow phototrophically with only light as its energy source. It uses the retinal containing and light-driven proton pump bacteriorhodopsin to enhance the membrane potential which drives the ATP synthase. Therefore, a model of the membrane potential generation of bacteriorhodopsin is of central importance to the development of a mathematical model of the bioenergetics of H. salinarum. To measure the current produced by bacteriorhodopsin at different light intensities and clamped voltages, we expressed the gene in Xenopus laevis oocytes. We present current-voltage measurements and a mathematical model of the current-voltage relationship of bacteriorhodopsin and its generation of the membrane potential. The model consists of three intermediate states, the BR, L, and M states, and comparisons between model predictions and experimental data show that the L to M reaction must be inhibited by the membrane potential. The model is not able to fit the current-voltage measurements when only the M to BR phase is membrane potential dependent, while it is able to do so when either only the L to M reaction or both reactions (L to M and M to BR) are membrane potential dependent. We also show that a decay term is necessary for modeling the rate of change of the membrane potential.
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Affiliation(s)
- Ricardo C H del Rosario
- Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
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Solid-state NMR and functional studies on proteorhodopsin. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:697-705. [DOI: 10.1016/j.bbabio.2009.02.022] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 02/16/2009] [Accepted: 02/17/2009] [Indexed: 11/19/2022]
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