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Feroz H, Ferlez B, Oh H, Mohammadiarani H, Ren T, Baker CS, Gajewski JP, Lugar DJ, Gaudana SB, Butler P, Hühn J, Lamping M, Parak WJ, Blatt MR, Kerfeld CA, Smirnoff N, Vashisth H, Golbeck JH, Kumar M. Liposome-based measurement of light-driven chloride transport kinetics of halorhodopsin. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183637. [PMID: 33930372 DOI: 10.1016/j.bbamem.2021.183637] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 04/14/2021] [Accepted: 04/22/2021] [Indexed: 11/30/2022]
Abstract
We report a simple and direct fluorimetric vesicle-based method for measuring the transport rate of the light-driven ions pumps as specifically applied to the chloride pump, halorhodopsin, from Natronomonas pharaonis (pHR). Previous measurements were cell-based and methods to determine average single channel permeability challenging. We used a water-in-oil emulsion method for directional pHR reconstitution into two different types of vesicles: lipid vesicles and asymmetric lipid-block copolymer vesicles. We then used stopped-flow experiments combined with fluorescence correlation spectroscopy to determine per protein Cl- transport rates. We obtained a Cl- transport rate of 442 (±17.7) Cl-/protein/s in egg phosphatidyl choline (PC) lipid vesicles and 413 (±26) Cl-/protein/s in hybrid block copolymer/lipid (BCP/PC) vesicles with polybutadine-polyethylene oxide (PB12PEO8) on the outer leaflet and PC in the inner leaflet at a photon flux of 1450 photons/protein/s. Normalizing to a per photon basis, this corresponds to 0.30 (±0.07) Cl-/photon and 0.28 (±0.04) Cl-/photon for pure PC and BCP/PC hybrid vesicles respectively, both of which are in agreement with recently reported turnover of ~500 Cl-/protein/s from flash photolysis experiments and with voltage-clamp measurements of 0.35 (±0.16) Cl-/photon in pHR-expressing oocytes as well as with a pHR quantum efficiency of ~30%.
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Affiliation(s)
- Hasin Feroz
- Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Bryan Ferlez
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
| | - Hyeonji Oh
- Department of Chemical Engineering, The University of Texas at Austin, Austin, TX, USA
| | | | - Tingwei Ren
- Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Carol S Baker
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
| | - John P Gajewski
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
| | - Daniel J Lugar
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
| | - Sandeep B Gaudana
- MSU-DOE Plant Research Laboratory and Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA
| | - Peter Butler
- Department of Biomedical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Jonas Hühn
- Department of Physics and Chemistry, Philipps University of Marburg, Marburg, Germany
| | - Matthias Lamping
- Department of Physics and Chemistry, Philipps University of Marburg, Marburg, Germany
| | - Wolfgang J Parak
- Center of Hybrid Nanostructures (CHyN), Universität Hamburg, Hamburg, Germany
| | - Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular Cell and Systems Biology, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK
| | - Cheryl A Kerfeld
- MSU-DOE Plant Research Laboratory and Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA; Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, USA; Environmental Genomics and Systems Biology and Molecular Biophysics and Integrated Bioimaging Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | | | - Harish Vashisth
- Department of Chemical Engineering, The University of New Hampshire, Durham, NH, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA; Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Manish Kumar
- Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, Austin, TX, USA.
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Feroz H, Ferlez B, Lefoulon C, Ren T, Baker CS, Gajewski JP, Lugar DJ, Gaudana SB, Butler PJ, Hühn J, Lamping M, Parak WJ, Hibberd JM, Kerfeld CA, Smirnoff N, Blatt MR, Golbeck JH, Kumar M. Light-Driven Chloride Transport Kinetics of Halorhodopsin. Biophys J 2019; 115:353-360. [PMID: 30021110 DOI: 10.1016/j.bpj.2018.06.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 05/19/2018] [Accepted: 06/05/2018] [Indexed: 01/25/2023] Open
Abstract
Despite growing interest in light-driven ion pumps for use in optogenetics, current estimates of their transport rates span two orders of magnitude due to challenges in measuring slow transport processes and determining protein concentration and/or orientation in membranes in vitro. In this study, we report, to our knowledge, the first direct quantitative measurement of light-driven Cl- transport rates of the anion pump halorohodopsin from Natronomonas pharaonis (NpHR). We used light-interfaced voltage clamp measurements on NpHR-expressing oocytes to obtain a transport rate of 219 (± 98) Cl-/protein/s for a photon flux of 630 photons/protein/s. The measurement is consistent with the literature-reported quantum efficiency of ∼30% for NpHR, i.e., 0.3 isomerizations per photon absorbed. To reconcile our measurements with an earlier-reported 20 ms rate-limiting step, or 35 turnovers/protein/s, we conducted, to our knowledge, novel consecutive single-turnover flash experiments that demonstrate that under continuous illumination, NpHR bypasses this step in the photocycle.
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Affiliation(s)
- Hasin Feroz
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania
| | - Bryan Ferlez
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania
| | - Cecile Lefoulon
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, United Kingdom
| | - Tingwei Ren
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania
| | - Carol S Baker
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania
| | - John P Gajewski
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania
| | - Daniel J Lugar
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania
| | - Sandeep B Gaudana
- MSU-DOE Plant Research Laboratory and Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan
| | - Peter J Butler
- Department of Biomedical Engineering, The Pennsylvania State University, University Park, Pennsylvania
| | - Jonas Hühn
- Department of Physics and Chemistry, Philipps University of Marburg, Marburg, Germany
| | - Matthias Lamping
- Department of Physics and Chemistry, Philipps University of Marburg, Marburg, Germany
| | - Wolfgang J Parak
- Department of Physics and Chemistry, Philipps University of Marburg, Marburg, Germany
| | - Julian M Hibberd
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Cheryl A Kerfeld
- MSU-DOE Plant Research Laboratory and Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan; Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, California; Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, California
| | | | - Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, United Kingdom
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania; Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania
| | - Manish Kumar
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania.
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Suresh M, Renugadevi B, Brammavidhya S, Iyapparaj P, Anantharaman P. Antibacterial Activity of Red Pigment Produced by Halolactibacillus alkaliphilus MSRD1—an Isolate from Seaweed. Appl Biochem Biotechnol 2015; 176:185-95. [DOI: 10.1007/s12010-015-1566-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2014] [Accepted: 03/12/2015] [Indexed: 11/28/2022]
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Furutani Y, Kimura T, Okamoto K. Development of a rapid Buffer-exchange system for time-resolved ATR-FTIR spectroscopy with the step-scan mode. Biophysics (Nagoya-shi) 2013; 9:123-9. [PMID: 27493550 PMCID: PMC4629687 DOI: 10.2142/biophysics.9.123] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Accepted: 07/16/2013] [Indexed: 12/31/2022] Open
Abstract
Attenuated total reflectance (ATR)-FTIR spectroscopy has been widely used to probe protein structural changes under various stimuli, such as light absorption, voltage change, and ligand binding, in aqueous conditions. Time-resolved measurements require a trigger, which can be controlled electronically; therefore, light and voltage changes are suitable. Here we developed a novel, rapid buffer-exchange system for time-resolved ATR-FTIR spectroscopy to monitor the ligand- or ion-binding re-action of a protein. By using the step-scan mode (time resolution; 2.5 ms), we confirmed the completion of the buffer-exchange reaction within ∼25 ms; the process was monitored by the infrared absorption change of a nitrate band at 1,350 cm(-1). We also demonstrated the anion-binding reaction of a membrane protein, Natronomonas pharaonis halorhodopsin (pHR), which binds a chloride ion in the initial anion-binding site near the retinal chromophore. The formation of chloride- or nitrate-bound pHR was confirmed by an increase of the retinal absorption band at 1,528 cm(-1). It also should be noted that low sample consumption (∼1 µg of protein) makes this new method a powerful technique to understand ligand-protein and ion-protein interactions, particularly for membrane proteins.
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Affiliation(s)
- Yuji Furutani
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Tetsunari Kimura
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Kido Okamoto
- UNISOKU Co., Ltd., 2-4-3 Kasugano, Hirakata, Osaka 573-0131, Japan
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Khanafari A, Khavarinejad D, Mashinchian A. Solar salt lake as natural environmental source for extraction halophilic pigments. IRANIAN JOURNAL OF MICROBIOLOGY 2010; 2:103-9. [PMID: 22347558 PMCID: PMC3279771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND AND OBJECTIVES Halophilic bacteria produce a variety of pigments, which function as immune modulators and have prophylactic action against cancers. In this study, colorful halophilic bacteria were isolated from solar salt lake and their pigments was extracted in optimal environmental conditions and compared with the pigments of Halorubrum sodomense ATCC 33755. MATERIALS AND METHODS Water samples from the solar salt lake in Imam Khomeini port in southwest of Iran were used as a source for isolation of pigment-producing bacteria. Halorubrum sodomense ATCC 33755 was used as control for pigment production. The conditions for optimum growth and pigment production were established for the isolated bacteria. Pigment were analyzed by spectrophotometer, TLC and NMR assay. The 16S rRNA genes were sequenced and results were used to differentiate haloarchaea from halophilic bacterial strains. RESULTS Among the isolated strains, YS and OS strains and Halorubrum sodomense were recognized as moderate and extremely halophile with maximum growth in the presence of 15% and 30% NaCl concentrations, respectively. Experiments conducted to find out the optimum conditions for growth and pigment production temperature at 25°C, pH = 7.2 and shaking conditions at 120 rpm for three strains. Without shaking, little growth with no pigment production was observed. Total pigment produced by red, yellow and orange strains was measured at 240, 880 and 560 mg per dry cell weight respectively. Amplification yielded bands of to isolated strains only observed with bacteria primers. This result suggesting the YS and OS strains were not haloarchaea. CONCLUSION The isolated halophilic bacteria produced much higher amounts of pigments than Halorubrum sodomense. Photo intermediates including metarhodopsin II (meta II, λ(max)=380 nm) were determined as major pigment in Halorubrum sodomense.
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Affiliation(s)
- A Khanafari
- Microbiology Department, North of Tehran Branch, Islamic Azad University,Corresponding author: Dr. A. Khanafari. Address: Microbiology Department, North of Tehran Branch, Islamic Azad University, Southern Makran Ave., Heravi Sq. Tehran, Iran. Tel.: +98-21-22950919. Fax: +98-21-22950920. E-mail:
| | - D Khavarinejad
- Marine Biology Department, Science and Research Branch, Islamic Azad University
| | - A Mashinchian
- Marine Biology Department, Science and Research Branch, Islamic Azad University
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Maiti TK, Engelhard M, Sheves M. Retinal-protein interactions in halorhodopsin from Natronomonas pharaonis: binding and retinal thermal isomerization catalysis. J Mol Biol 2009; 394:472-84. [PMID: 19766652 DOI: 10.1016/j.jmb.2009.09.024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 09/07/2009] [Accepted: 09/14/2009] [Indexed: 11/29/2022]
Abstract
Halorhodopsin from Natronomonas pharaonis (NpHR) is a member of the retinal protein group and serves as a light-driven chloride pump in which chloride ions are transported through the membrane following light absorption by the retinal chromophore. In this study, we examined two main issues: (1) factors controlling the binding of the retinal chromophore to the NpHR opsin and (2) the ability of the NpHR opsin to catalyze the thermal isomerization of retinal isomers. We have revealed that the reconstitution process of pharaonis HR (NpHR) pigment from its apoprotein and all-trans retinal depends on the pH, and the process has a pK(a) of 5.8+/-0.1. It was proposed that this pK(a) is associated with the pK(a) of the lysine residue that binds the retinal chromophore (Lys256). The pigment formation is regulated by the concentration of sodium chloride, and the maximum yield was observed at 3.7 M NaCl. The low yield of pigment in a lower concentration of NaCl (<3 M) may be due to an altered conformation adopted by the apomembrane, which is not capable of forming the pigment. Unexpectedly and unlike the apomembrane of bacteriorhodopsin, NpHR opsin produces pigments with 11-cis retinal and 9-cis retinal owing to the thermal isomerization of these retinal isomers to all-trans retinal. The isomerization rate depends on the pH, and it is faster at a higher pH. The pK(a) value of the isomerization process is similar to the pK(a) of the binding process of these retinals, which suggests that Lys256 is also involved in the isomerization process. The isomerization is independent of the sodium chloride concentration. However, in the absence of sodium chloride, the apoprotein adopts such a conformation, which does not prevent the isomerization of retinal, but it prevents a covalent bond formation with the lysine residue. The rate and the thermodynamic parameter analysis of the retinal isomerization by NpHR apoprotein led to the conclusion that the apomembrane catalyzes the isomerization via a triplet mechanism.
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Affiliation(s)
- Tushar Kanti Maiti
- Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, Israel
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7
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Inoue K, Kubo M, Demura M, Kamo N, Terazima M. Reaction dynamics of halorhodopsin studied by time-resolved diffusion. Biophys J 2009; 96:3724-34. [PMID: 19413978 DOI: 10.1016/j.bpj.2008.12.3932] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 12/24/2008] [Accepted: 12/31/2008] [Indexed: 11/26/2022] Open
Abstract
Reaction dynamics of a chloride ion pump protein, halorhodopsin (HR), from Natronomonas pharaonis (N. pharaonis) (NpHR) was studied by the pulsed-laser-induced transient grating (TG) method. A detailed investigation of the TG signal revealed that there is a spectrally silent diffusion process besides the absorption-observable reaction dynamics. We interpreted these dynamics in terms of release, diffusion, and uptake of the Cl(-) ion. From a quantitative global analysis of the signals at various grating wavenumbers, it was concluded that the release of the Cl(-) ion is associated with the L2 --> (L2 (or N) <==> O) process, and uptake of Cl(-) occurs with the (L2 (or N) <==> O) -->NpHR' process. The diffusion coefficient of NpHR solubilized in a detergent did not change during the cyclic reaction. This result contrasts the behavior of many photosensor proteins and implies that the change in the H-bond network from intra- to intermolecular is not significant for the activity of this protein pump.
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Affiliation(s)
- Keiichi Inoue
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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Kubo M, Kikukawa T, Miyauchi S, Seki A, Kamiya M, Aizawa T, Kawano K, Kamo N, Demura M. Role of Arg123 in Light-driven Anion Pump Mechanisms ofpharaonisHalorhodopsin. Photochem Photobiol 2009; 85:547-55. [DOI: 10.1111/j.1751-1097.2009.00538.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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9
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Seki A, Miyauchi S, Hayashi S, Kikukawa T, Kubo M, Demura M, Ganapathy V, Kamo N. Heterologous expression of Pharaonis halorhodopsin in Xenopus laevis oocytes and electrophysiological characterization of its light-driven Cl- pump activity. Biophys J 2007; 92:2559-69. [PMID: 17208978 PMCID: PMC1864822 DOI: 10.1529/biophysj.106.093153] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Natronomonas pharaonis halorhodopsin (pHR) is an archaeal rhodopsin functioning as an inward-directed, light-driven Cl- pump. To characterize the electrophysiological features of the Cl- pump activity of pHR, we expressed pHR in Xenopus laevis oocytes and analyzed its photoinduced Cl- pump activity using the two-electrode voltage-clamp technique. Photoinduced outward currents were observed only in the presence of Cl-, Br-, I-, NO3-, and SCN-, but not in control oocytes, indicating that photoinduced anion currents were mediated by pHR. The relationship between photoinduced Cl- current via pHR and the light intensity was linear, demonstrating that transport of Cl- is driven by a single-photon reaction and that the steady-state current is proportional to the excited pHR molecule. The current-voltage relationship for pHR-mediated photoinduced currents was also linear between -150 mV and +50 mV. The slope of the line describing the current-voltage relationship increased as the number of the excited pHR molecules was increased by the light intensity. The reversal potential (VR) for Cl- as the substrate for the anion pump activity of pHR was about -400 mV. The value for VR was independent of light intensity, meaning that the VR reflects the intrinsic value of the excited pHR molecule. The value of VR changed significantly for the R123K mutant of pHR. We also show that the Cl- pump activity of pHR can generate a substantial negative membrane potential, indicating that pHR is a very potent Cl- pump. We have also analyzed the kinetics of voltage-dependent Cl- pump activity as well as that of the photocycle. Based on these data, a kinetic model for voltage-dependent Cl- transport via pHR is presented.
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Affiliation(s)
- Akiteru Seki
- Graduate School of Pharmaceutical Sciences, Laboratory of Biomolecular Systems, Creative Research Initiative Sosei, and Department of Biomolecular Science, Faculty of Advanced Life Sciences, Hokkaido University, Sapporo, Japan
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Roy S, Kulshrestha K. All-optical switching in plant blue light photoreceptor phototropin. IEEE Trans Nanobioscience 2006; 5:281-7. [PMID: 17181028 DOI: 10.1109/tnb.2006.886549] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We theoretically analyze all-optical switching in the recently characterized LOV2 domain from Avena sativa (oat) phot1 phototropin, a blue-light plant photoreceptor, based on nonlinear intensity-induced excited-state absorption. The transmission of a cw probe laser beam at 660 nm corresponding to the peak absorption of the first excited L-state, through the LOV2 sample, is switched by a pulsed pump laser beam at 442 nm that corresponds to the maximum initial D state absorption. The switching characteristics have been analyzed using the rate equation approach, considering all the three intermediate states and transitions in the LOV2 photocycle. It is shown that for a given pump pulse intensity, there is an optimum pump pulsewidth for which the switching contrast is maximum. It is shown that the probe laser beam can be completely switched off (100% modulation) by the pump laser beam at 50 kW/cm2 for a concentration of 1 mM with sample thickness of 5.5 mm. The switching characteristics are sensitive to various parameters such as concentration, rate constant of L-state, peak pump intensity and pump pulse width. At typical values, the switch-off and switch-on time is 1.6 and 22.3 micros, respectively. The switching characteristics have also been used to design all-optical NOT and the universal NOR and NAND logic gates.
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Affiliation(s)
- Sukhdev Roy
- Department of Physics and Computer Science, Dayalbagh Educational Institute, Deemed University, Agra 282 005, India.
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Magyari K, Simon V, Váró G. The influence of the halide ions on the photochemical reaction cycle of pharaonis halorhodopsin. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2006; 82:16-20. [PMID: 16219469 DOI: 10.1016/j.jphotobiol.2005.08.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Revised: 08/04/2005] [Accepted: 08/08/2005] [Indexed: 11/27/2022]
Abstract
Sodium salt of chloride, bromide and iodide were used to elucidate the effect of the size of the anion on the binding to pharaonis halorhodopsin and its transport during the photocycle of this retinal protein. Spectroscopic titration revealed an apparent strong binding constant of 2 mM for chloride, 0.23 mM for bromide and 5 mM for iodide. In the case of iodide a second, week binding constant of about 10 M could be estimated. This second binding constant was similar to that observed earlier for nitrate. By changing the halide ions, only the transitions in the second half of the photocycle were affected, which contained intermediates N, O, and HR'. The O to HR' transition becomes faster with increasing ion volume, meaning that the ion uptake is accelerated. This effect shows a direct correlation with the ion radius. With increasing ion concentration the N-O-HR' equilibrium changed in such a way that the accumulated O tended to decrease. This tendency was overruled in iodide, by the appearance of the second binding constant. The increasing iodide concentration, up to 100mM decreases the accumulation of the intermediate O, due to kinetic reasons, but at higher ion concentration the amount of O increases, although its decay becomes faster. This effect correlates with the appearance of the second iodide bound to the protein.
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Affiliation(s)
- Klára Magyari
- Department of Physics, University "Babes-Bolyai" Cluj-Napoca, Romania
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Szakács J, Lakatos M, Ganea C, Váró G. Kinetic isotope effects in the photochemical reaction cycle of ion transporting retinal proteins. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2005; 79:145-50. [PMID: 15878119 DOI: 10.1016/j.jphotobiol.2005.01.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2004] [Revised: 01/05/2005] [Accepted: 01/06/2005] [Indexed: 11/28/2022]
Abstract
The kinetics of the photochemical reaction cycle of the bacteriorhodopsin, pharaonis halorhodopsin and proteorhodopsin were determined in H2O and D2O at low and high pH, to get insight in the proton dependent steps of the transport process. While all the steps of the bacteriorhodopsin photocycle at normal pH exhibited a strong isotope effect, the proton uptake step of the photocycle, measured at high pH, became independent of deuterium exchange, making plausible that this step, at low proton concentration, becomes concentration dependent, not mobility dependent. The proton transporting photocycle of the proteorhodopsin at its normal pH (9.5) shows a marked deuterium effect, while at high pH (12.2) this effect almost totally disappears. It was shown earlier that the proton uptake step of the proteorhodopsin is at the rise of the N form. As the proton concentration decreases with rising pH this step becomes the rate limiting, proton concentration dependent step, hiding all the other isotope dependent components. In the case of halorhodopsin in all the chloride, nitrate and proton transporting conditions the photocycle was not strongly affected by the deuterium exchange. While in the cases of the first two ions this seems normal, the absence of the deuterium effect in the case of the proton transporting photocycle was a puzzle. The only plausible explanation is that in the presence of azide the halorhodopsin transports not the proton, but a negatively charged ion the OH-, the mass and mobility of which is only slightly influenced by the deuterium exchange.
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Affiliation(s)
- Júliánna Szakács
- Department of Biophysics, University of Medicine and Pharmacy, Tg. Mures, Romania
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