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Photochemical reaction cycle transitions during anion channelrhodopsin gating. Proc Natl Acad Sci U S A 2016; 113:E1993-2000. [PMID: 27001860 DOI: 10.1073/pnas.1525269113] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A recently discovered family of natural anion channelrhodopsins (ACRs) have the highest conductance among channelrhodopsins and exhibit exclusive anion selectivity, which make them efficient inhibitory tools for optogenetics. We report analysis of flash-induced absorption changes in purified wild-type and mutant ACRs, and of photocurrents they generate in HEK293 cells. Contrary to cation channelrhodopsins (CCRs), the ion conducting state of ACRs develops in an L-like intermediate that precedes the deprotonation of the retinylidene Schiff base (i.e., formation of an M intermediate). Channel closing involves two mechanisms leading to depletion of the conducting L-like state: (i) Fast closing is caused by a reversible L⇔M conversion. Glu-68 in Guillardia theta ACR1 plays an important role in this transition, likely serving as a counterion and proton acceptor at least at high and neutral pH. Incomplete suppression of M formation in the GtACR1_E68Q mutant indicates the existence of an alternative proton acceptor. (ii) Slow closing of the channel parallels irreversible depletion of the M-like and, hence, L-like state. Mutation of Cys-102 that strongly affected slow channel closing slowed the photocycle to the same extent. The L and M intermediates were in equilibrium in C102A as in the WT. In the position of Glu-123 in channelrhodopsin-2, ACRs contain a noncarboxylate residue, the mutation of which to Glu produced early Schiff base proton transfer and strongly inhibited channel activity. The data reveal fundamental differences between natural ACR and CCR conductance mechanisms and their underlying photochemistry, further confirming that these proteins form distinct families of rhodopsin channels.
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2
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Harris A, Ljumovic M, Bondar AN, Shibata Y, Ito S, Inoue K, Kandori H, Brown LS. A new group of eubacterial light-driven retinal-binding proton pumps with an unusual cytoplasmic proton donor. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:1518-29. [PMID: 26260121 DOI: 10.1016/j.bbabio.2015.08.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 08/05/2015] [Accepted: 08/05/2015] [Indexed: 10/23/2022]
Abstract
One of the main functions of microbial rhodopsins is outward-directed light-driven proton transport across the plasma membrane, which can provide sources of energy alternative to respiration and chlorophyll photosynthesis. Proton-pumping rhodopsins are found in Archaea (Halobacteria), multiple groups of Bacteria, numerous fungi, and some microscopic algae. An overwhelming majority of these proton pumps share the common transport mechanism, in which a proton from the retinal Schiff base is first transferred to the primary proton acceptor (normally an Asp) on the extracellular side of retinal. Next, reprotonation of the Schiff base from the cytoplasmic side is mediated by a carboxylic proton donor (Asp or Glu), which is located on helix C and is usually hydrogen-bonded to Thr or Ser on helix B. The only notable exception from this trend was recently found in Exiguobacterium, where the carboxylic proton donor is replaced by Lys. Here we describe a new group of efficient proteobacterial retinal-binding light-driven proton pumps which lack the carboxylic proton donor on helix C (most often replaced by Gly) but possess a unique His residue on helix B. We characterize the group spectroscopically and propose that this histidine forms a proton-donating complex compensating for the loss of the carboxylic proton donor.
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Affiliation(s)
- Andrew Harris
- Department of Physics, University of Guelph, ON, Canada
| | | | | | - Yohei Shibata
- Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan
| | - Shota Ito
- Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan
| | - Keiichi Inoue
- Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan; PRESTO, Japan Science and Technology Agency, Japan
| | - Hideki Kandori
- Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan.
| | - Leonid S Brown
- Department of Physics, University of Guelph, ON, Canada.
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3
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Balashov SP, Imasheva ES, Dioumaev A, Wang JM, Jung KH, Lanyi JK. Light-driven Na(+) pump from Gillisia limnaea: a high-affinity Na(+) binding site is formed transiently in the photocycle. Biochemistry 2014; 53:7549-61. [PMID: 25375769 PMCID: PMC4263435 DOI: 10.1021/bi501064n] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 10/17/2014] [Indexed: 02/06/2023]
Abstract
A group of microbial retinal proteins most closely related to the proton pump xanthorhodopsin has a novel sequence motif and a novel function. Instead of, or in addition to, proton transport, they perform light-driven sodium ion transport, as reported for one representative of this group (KR2) from Krokinobacter. In this paper, we examine a similar protein, GLR from Gillisia limnaea, expressed in Escherichia coli, which shares some properties with KR2 but transports only Na(+). The absorption spectrum of GLR is insensitive to Na(+) at concentrations of ≤3 M. However, very low concentrations of Na(+) cause profound differences in the decay and rise time of photocycle intermediates, consistent with a switch from a "Na(+)-independent" to a "Na(+)-dependent" photocycle (or photocycle branch) at ∼60 μM Na(+). The rates of photocycle steps in the latter, but not the former, are linearly dependent on Na(+) concentration. This suggests that a high-affinity Na(+) binding site is created transiently after photoexcitation, and entry of Na(+) from the bulk to this site redirects the course of events in the remainder of the cycle. A greater concentration of Na(+) is needed for switching the reaction path at lower pH. The data suggest therefore competition between H(+) and Na(+) to determine the two alternative pathways. The idea that a Na(+) binding site can be created at the Schiff base counterion is supported by the finding that upon perturbation of this region in the D251E mutant, Na(+) binds without photoexcitation. Binding of Na(+) to the mutant shifts the chromophore maximum to the red like that of H(+), which occurs in the photocycle of the wild type.
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Affiliation(s)
- Sergei P. Balashov
- Department
of Physiology and Biophysics, University
of California, Irvine, California 92697, United States
| | - Eleonora S. Imasheva
- Department
of Physiology and Biophysics, University
of California, Irvine, California 92697, United States
| | - Andrei
K. Dioumaev
- Department
of Physiology and Biophysics, University
of California, Irvine, California 92697, United States
| | - Jennifer M. Wang
- Department
of Physiology and Biophysics, University
of California, Irvine, California 92697, United States
| | - Kwang-Hwan Jung
- Department
of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Shinsu-Dong 1, Mapo-Gu, Seoul 121-742, Korea
| | - Janos K. Lanyi
- Department
of Physiology and Biophysics, University
of California, Irvine, California 92697, United States
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4
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Ranaghan MJ, Greco JA, Wagner NL, Grewal R, Rangarajan R, Koscielecki JF, Wise KJ, Birge RR. Photochromic bacteriorhodopsin mutant with high holographic efficiency and enhanced stability via a putative self-repair mechanism. ACS APPLIED MATERIALS & INTERFACES 2014; 6:2799-2808. [PMID: 24498928 PMCID: PMC3985900 DOI: 10.1021/am405363z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 02/05/2014] [Indexed: 06/03/2023]
Abstract
The Q photoproduct of bacteriorhodopsin (BR) is the basis of several biophotonic technologies that employ BR as the photoactive element. Several blue BR (bBR) mutants, generated by using directed evolution, were investigated with respect to the photochemical formation of the Q state. We report here a new bBR mutant, D85E/D96Q, which is capable of efficiently converting the entire sample to and from the Q photoproduct. At pH 8.5, where Q formation is optimal, the Q photoproduct requires 65 kJ mol(-1) of amber light irradiation (590 nm) for formation and 5 kJ mol(-1) of blue light (450 nm) for reversion, respectively. The melting temperature of the resting state and Q photoproduct, measured via differential scanning calorimetry, is observed at 100 °C and 89 °C at pH 8.5 or 91 °C and 82 °C at pH 9.5, respectively. We hypothesize that the protein stability of D85E/D96Q compared to other blue mutants is associated with a rapid equilibrium between the blue form E85(H) and the purple form E85(-) of the protein, the latter providing enhanced structural stability. Additionally, the protein is shown to be stable and functional when suspended in an acrylamide matrix at alkaline pH. Real-time photoconversion to and from the Q state is also demonstrated with the immobilized protein. Finally, the holographic efficiency of an ideal thin film using the Q state of D85E/D96Q is calculated to be 16.7%, which is significantly better than that provided by native BR (6-8%) and presents the highest efficiency of any BR mutant to date.
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Affiliation(s)
- Matthew J. Ranaghan
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Jordan A. Greco
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Nicole L. Wagner
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Rickinder Grewal
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Rekha Rangarajan
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Jeremy F. Koscielecki
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Kevin J. Wise
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
| | - Robert R. Birge
- Department of Molecular and Cell Biology, University of Connecticut, 91 North Eagleville Road, Storrs, Connecticut 06269, United States
- Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, Connecticut 06269, United States
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Moltke S, Alexiev U, Heyn MP. Kinetics of Light-Induced Intramolecular Charge Transfer and Proton Release in Bacteriorhodopsin. Isr J Chem 2013. [DOI: 10.1002/ijch.199500039] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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7
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Wagner NL, Greco JA, Ranaghan MJ, Birge RR. Directed evolution of bacteriorhodopsin for applications in bioelectronics. J R Soc Interface 2013; 10:20130197. [PMID: 23676894 DOI: 10.1098/rsif.2013.0197] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In nature, biological systems gradually evolve through complex, algorithmic processes involving mutation and differential selection. Evolution has optimized biological macromolecules for a variety of functions to provide a comparative advantage. However, nature does not optimize molecules for use in human-made devices, as it would gain no survival advantage in such cooperation. Recent advancements in genetic engineering, most notably directed evolution, have allowed for the stepwise manipulation of the properties of living organisms, promoting the expansion of protein-based devices in nanotechnology. In this review, we highlight the use of directed evolution to optimize photoactive proteins, with an emphasis on bacteriorhodopsin (BR), for device applications. BR, a highly stable light-activated proton pump, has shown great promise in three-dimensional optical memories, real-time holographic processors and artificial retinas.
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Affiliation(s)
- Nicole L Wagner
- Department of Molecular & Cell Biology, University of Connecticut, Storrs, CT 06269-3125, USA
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8
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Fu HY, Yi HP, Lu YH, Yang CS. Insight into a single halobacterium using a dual-bacteriorhodopsin system with different functionally optimized pH ranges to cope with periplasmic pH changes associated with continuous light illumination. Mol Microbiol 2013; 88:551-61. [DOI: 10.1111/mmi.12208] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/10/2013] [Indexed: 11/29/2022]
Affiliation(s)
- Hsu-Yuan Fu
- Department of Biochemical Science and Technology; College of Life Science; National Taiwan University; No. 1, Sec. 4, Roosevelt Rd. Taipei Taiwan 10617
| | - Hsiu-Ping Yi
- Department of Biochemical Science and Technology; College of Life Science; National Taiwan University; No. 1, Sec. 4, Roosevelt Rd. Taipei Taiwan 10617
| | - Yen-Hsu Lu
- Department of Biochemical Science and Technology; College of Life Science; National Taiwan University; No. 1, Sec. 4, Roosevelt Rd. Taipei Taiwan 10617
| | - Chii-Shen Yang
- Department of Biochemical Science and Technology; College of Life Science; National Taiwan University; No. 1, Sec. 4, Roosevelt Rd. Taipei Taiwan 10617
- Institute of Biotechnology; College of Bio-Resources and Agriculture; National Taiwan University; No. 1, Sec. 4, Roosevelt Rd. Taipei Taiwan 10617
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9
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Saint Clair EC, Ogren JI, Mamaev S, Russano D, Kralj JM, Rothschild KJ. Near-IR resonance Raman spectroscopy of archaerhodopsin 3: effects of transmembrane potential. J Phys Chem B 2012. [PMID: 23189985 DOI: 10.1021/jp309996a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Archaerhodopsin 3 (AR3) is a light driven proton pump from Halorubrum sodomense that has been used as a genetically targetable neuronal silencer and an effective fluorescent sensor of transmembrane potential. Unlike the more extensively studied bacteriorhodopsin (BR) from Halobacterium salinarum, AR3 readily incorporates into the plasma membrane of both E. coli and mammalian cells. Here, we used near-IR resonance Raman confocal microscopy to study the effects of pH and membrane potential on the AR3 retinal chromophore structure. Measurements were performed both on AR3 reconstituted into E. coli polar lipids and in vivo in E. coli expressing AR3 in the absence and presence of a negative transmembrane potential. The retinal chromophore structure of AR3 is in an all-trans configuration almost identical to BR over the entire pH range from 3 to 11. Small changes are detected in the retinal ethylenic stretching frequency and Schiff Base (SB) hydrogen bonding strength relative to BR which may be related to a different water structure near the SB. In the case of the AR3 mutant D95N, at neutral pH an all-trans retinal O-like species (O(all-trans)) is found. At higher pH a second 13-cis retinal N-like species (N(13-cis)) is detected which is attributed to a slowly decaying intermediate in the red-light photocycle of D95N. However, the amount of N(13-cis) detected is less in E. coli cells but is restored upon addition of carbonyl cyanide m-chlorophenyl hydrazone (CCCP) or sonication, both of which dissipate the normal negative membrane potential. We postulate that these changes are due to the effect of membrane potential on the N(13-cis) to M(13-cis) levels accumulated in the D95N red-light photocycle and on a molecular level by the effects of the electric field on the protonation/deprotonation of the cytoplasmic accessible SB. This mechanism also provides a possible explanation for the observed fluorescence dependence of AR3 and other microbial rhodopsins on transmembrane potential.
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Affiliation(s)
- Erica C Saint Clair
- Department of Physics, Photonics Center and Molecular Biophysics Laboratory, Boston University, Boston, Massachusetts 02215, USA
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10
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Imhof M, Rhinow D, Linne U, Hampp N. Two-Photon-Induced Selective Decarboxylation of Aspartic Acids D85 and D212 in Bacteriorhodopsin. J Phys Chem Lett 2012; 3:2991-2994. [PMID: 26292239 DOI: 10.1021/jz301292n] [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: 06/04/2023]
Abstract
The interest in microbial opsins stems from their photophysical properties, which are superior to most organic dyes. Microbial rhodopsins like bacteriorhodopsin (BR) from Halobacterium salinarum have an astonishingly high cross-section for two-photon-absorption (TPA), which is of great interest for technological applications such as data storage. Irradiation of BR with intense laser pulses at 532 nm leads to formation of a bathochromic photoproduct, which is further converted to a photochemical species absorbing in the UV range. As demonstrated earlier, the photochemical conversions are induced by resonant TPA. However, the molecular basis of these conversions remained unresolved. In this work we use mass spectroscopy to demonstrate that TPA of BR leads to selective decarboxylation of two aspartic acids in the vicinity of the retinal chromphore. These photochemical conversions are the basis of permanent two-photon data storage in BR and are of critical importance for application of microbial opsins in optogenetics.
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Affiliation(s)
- Martin Imhof
- †Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str., D-35032 Marburg, Germany
| | - Daniel Rhinow
- ‡Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany
| | - Uwe Linne
- †Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str., D-35032 Marburg, Germany
| | - Norbert Hampp
- †Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str., D-35032 Marburg, Germany
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11
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Pescitelli G, Woody RW. The Exciton Origin of the Visible Circular Dichroism Spectrum of Bacteriorhodopsin. J Phys Chem B 2012; 116:6751-63. [DOI: 10.1021/jp212166k] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gennaro Pescitelli
- Dipartimento
di Chimica e Chimica
Industriale, Università degli Studi di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
| | - Robert W. Woody
- Department of Biochemistry and
Molecular Biology, Colorado State University, Fort Collins, Colorado 80523, United States
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12
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Baumann RP, Eussner J, Hampp N. pH-dependent bending in and out of purple membranes comprising BR-D85T. Phys Chem Chem Phys 2011; 13:21375-82. [DOI: 10.1039/c1cp22098e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Rhinow D, Chizhik I, Baumann RP, Noll F, Hampp N. Crystallinity of Purple Membranes Comprising the Chloride-Pumping Bacteriorhodopsin Variant D85T and Its Modulation by pH and Salinity. J Phys Chem B 2010; 114:15424-8. [DOI: 10.1021/jp108502p] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Daniel Rhinow
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany, Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str. Bldg. H, D-35032 Marburg, Germany, and Material Sciences Center, D-35032 Marburg, Germany
| | - Ivan Chizhik
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany, Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str. Bldg. H, D-35032 Marburg, Germany, and Material Sciences Center, D-35032 Marburg, Germany
| | - Roelf-Peter Baumann
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany, Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str. Bldg. H, D-35032 Marburg, Germany, and Material Sciences Center, D-35032 Marburg, Germany
| | - Frank Noll
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany, Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str. Bldg. H, D-35032 Marburg, Germany, and Material Sciences Center, D-35032 Marburg, Germany
| | - Norbert Hampp
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60438 Frankfurt, Germany, Philipps-University of Marburg, Department of Chemistry, Hans-Meerwein-Str. Bldg. H, D-35032 Marburg, Germany, and Material Sciences Center, D-35032 Marburg, Germany
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Baumann RP, Schranz M, Hampp N. Bending of purple membranes in dependence on the pH analyzed by AFM and single molecule force spectroscopy. Phys Chem Chem Phys 2010; 12:4329-35. [DOI: 10.1039/b919729j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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15
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Fujimoto KJ, Asai K, Hasegawa JY. Theoretical study of the opsin shift of deprotonated retinal schiff base in the M state of bacteriorhodopsin. Phys Chem Chem Phys 2010; 12:13107-16. [DOI: 10.1039/c0cp00361a] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Lazarova T, Querol E, Padrós E. Coupling between the retinal thermal isomerization and the Glu194 residue of bacteriorhodopsin. Photochem Photobiol 2009; 85:617-23. [PMID: 19267876 DOI: 10.1111/j.1751-1097.2008.00534.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Glu194 is a residue located at the end of F helix on the extracellular side of the light-induced proton pump bacteriorhodopsin (BR). Currently, it is well recognized that Glu194 and Glu204 residues, along with water clusters, constitute the proton release group of BR. Here we report that the replacement of Glu194 for Gln affects not only the photocycle of the protein but also has tremendous effect on the all-trans to 13-cis thermal isomerization. We studied the pH dependence of the dark adaptation of the E194Q mutant and performed HPLC analysis of the isomer compositions of the light- and partially dark-adapted states of the mutant at several pH values. Our data confirmed that E194Q exhibits extremely slow dark adaptation over a wide range of pH. HPLC data showed that a significantly larger concentration of all-trans isomer was present in the samples of the E194Q mutant even after prolonged dark adaptation. After 14 days in the dark the 13-cis to all-trans ratio was 1:3 in the mutant, compared to 2:1 in the wild type. These data clearly indicate the involvement of Glu194 in control of the rate of all-trans to 13-cis thermal isomerization.
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Affiliation(s)
- Tzvetana Lazarova
- Departament de Bioquímica i de Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, Spain.
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Mutagenic Analysis of Membrane Protein Functional Mechanisms: Bacteriorhodopsin as a Model Example. Methods Cell Biol 2008. [DOI: 10.1016/s0091-679x(07)84016-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Lanyi JK. Studies of the Bacteriorhodopsin Photocycle without the Use of Light: Clues to Proton Transfer Coupled Reactions. J Mol Microbiol Biotechnol 2007; 12:210-7. [PMID: 17587869 DOI: 10.1159/000099642] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In the photochemical cycle of bacteriorhodopsin, the light-driven proton pump of halobacteria, only the first step, the isomerization of the all-trans retinal to 13-cis, is dependent on illumination. Because the steps that accomplish the translocation of a proton during the ensuing reaction sequence of intermediate states are thermal reactions, they have direct analogies with such steps in other ion pumps. In a surprisingly large number of cases, the reactions of the photocycle could be studied without using light. This review recounts experiments of this kind, and what they contribute to understanding the transport mechanism of this pump, and perhaps indirectly other ion pumps as well.
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Affiliation(s)
- Janos K Lanyi
- Department of Physiology and Biophysics, University of California, Irvine, California 92697-4560, USA.
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Abstract
Xanthorhodopsin (XR), the light-driven proton pump of the halophilic eubacterium Salinibacter ruber, exhibits substantial homology to bacteriorhodopsin (BR) of archaea and proteorhodopsin (PR) of marine bacteria, but unlike them contains a light-harvesting carotenoid antenna, salinixanthin, as well as retinal. We report here the pH-dependent properties of XR. The pKa of the retinal Schiff base is as high as in BR, i.e. > or =12.4. Deprotonation of the Schiff base and the ensuing alkaline denaturation cause large changes in the absorption bands of the carotenoid antenna, which lose intensity and become broader, making the spectrum similar to that of salinixanthin not bound to XR. A small redshift of the retinal chromophore band and increase of its extinction, as well as the pH-dependent amplitude of the M intermediate indicate that in detergent-solubilized XR the pKa of the Schiff base counterion and proton acceptor is about 6 (compared to 2.6 in BR, and 7.5 in PR). The protonation of the counterion is accompanied by a small blueshift of the carotenoid absorption bands. The pigment is stable in the dark upon acidification to pH 2. At pH < 2 a transition to a blueshifted species absorbing around 440 nm occurs, accompanied by loss of resolution of the carotenoid absorption bands. At pH < 3 illumination of XR with continuous light causes accumulation of long-lived photoproduct(s) with an absorption maximum around 400 nm. The photocycle of XR was examined between pH 4 and 10 in solubilized samples. The pH dependence of recovery of the initial state slows at both acid and alkaline pH, with pKas of 6.0 and 9.3. The decrease in the rates with pKa 6.0 is apparently caused by protonation of the counterion and proton acceptor, and that at high pH reflects the pKa of the internal proton donor, Glu94, at the times in the photocycle when this group equilibrates with the bulk.
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Affiliation(s)
| | - Sergei P. Balashov
- To whom correspondence should be addressed: Department of Physiology & Biophysics, D-340 Medical Science I, University of California, Irvine, CA 92697-4560 , Phone: (949) 824-7783, Fax: (949) 824-8540,
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21
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Lukashev EP, Pronskaya NA. Photochemical properties of a bacteriorhodopsin analog with 13-demethyl-13-trifluoromethyl retinal. Biophysics (Nagoya-shi) 2006. [DOI: 10.1134/s0006350906030092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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22
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Wang L, Shen Z, Wang J, Li B, Chen F, Yang W, Feng X. The pH-dependence of photochemical intermediates of O and P in bacteriorhodopsin by continuous light. Biochem Biophys Res Commun 2006; 343:899-903. [PMID: 16564498 DOI: 10.1016/j.bbrc.2006.03.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2006] [Accepted: 03/07/2006] [Indexed: 05/08/2023]
Abstract
The pH-dependence of the O and P intermediates in the photocycle of bacteriorhodopsin (bR) on the intensity and duration of the exciting flash was investigated for bR glycerol suspensions and bR gelatin films. Green and red laser flashes (532 and 670 nm) were utilized to generate a photoequilibrium state of bR and O at ambient temperature, and UV-vis spectroscopy was used to determine the photoconversion for the bR suspensions and films. The maximal concentration of the O intermediate was observed to be pH-dependent and the dependency was most pronounced at a slightly alkaline pH values. The photochemical conversion from the O to P intermediate was investigated for both bR suspensions and films. The P intermediate was only found in bR gelatin film. These results indicate that bR gelatin film may be an attractive candidate for the information storage based on P intermediate. It is possible, with red light, to create photoproducts which are thermally stable at ambient temperature and that can be photochemically erased.
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Affiliation(s)
- Liping Wang
- School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China.
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23
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Mason AJ, Turner GJ, Glaubitz C. Conformational heterogeneity of transmembrane residues after the Schiff base reprotonation of bacteriorhodopsin. FEBS J 2005; 272:2152-64. [PMID: 15853800 DOI: 10.1111/j.1742-4658.2005.04633.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
bR, N-like and O-like intermediate states of [15N]methionine-labelled wild type and D85N/T170C bacteriorhodopsin were accumulated in native membranes by controlling the pH of the preparations. 15N cross polarization and magic angle sample spinning (CPMAS) NMR spectroscopy allowed resolution of seven out of nine resonances in the bR-state. It was possible to assign some of the observed resonances by using 13C/15N rotational echo double resonance (REDOR) NMR and Mn2+ quenching as well as D2O exchange, which helps to identify conformational changes after the bacteriorhodopsin Schiff base reprotonation. The significant differences in chemical shifts and linewidths detected for some of the resonances in N- and O-like samples indicate changes in conformation, structural heterogeneity or altered molecular dynamics in parts of the protein.
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Affiliation(s)
- A James Mason
- Centre for Biomolecular Magnetic Resonance and Institut für Biophysikalische Chemie, J.W. Goethe Universität, Frankfurt, Germany
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24
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Luecke H, Lanyi JK. Structural clues to the mechanism of ion pumping in bacteriorhodopsin. ADVANCES IN PROTEIN CHEMISTRY 2003; 63:111-30. [PMID: 12629968 DOI: 10.1016/s0065-3233(03)63005-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Hartmut Luecke
- Departments of Biochemistry, Biophysics and Computer Science, University of California, Irvine, California 92697, USA
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25
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Martinez LC, Turner GJ. High-throughput screening of bacteriorhodopsin mutants in whole cell pastes. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1564:91-8. [PMID: 12101000 DOI: 10.1016/s0005-2736(02)00406-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A high-throughput screening method has been developed which enables functional analysis of bacteriorhodpsin in whole cell pastes. Reflectance spectra, from as little as 5 ml of Halobacterium salinarum cells, show close correspondence to that obtained from the purified purple membrane (PM), containing bacteriorhodopsin (BR) as the sole protein component. We demonstrate accurate quantification of BR accumulation by ratiometric analysis of BR (A(max) 568) and a membrane-bound cytochrome (A(max) 410). In addition, ground-state light- and dark-adapted (LA and DA, respectively) spectral differences were determined with high accuracy and precision. Using cells expressing the BR mutant D85N, we monitored transitions between intermediate-state homologues of the reprotonation phase of the light-activated proton pumping mechanism. We demonstrate that phenotypes of three mutants (D85N/T170C, D85N/D96N, and D85N/R82Q) previously characterized for their effect on photocycle transitions are reproduced in the whole cell samples. D85N/T170C stabilizes accumulation of the N state while D85N/D96N accumulates no N state. D85N/R82Q was found to have perturbed the pK(a) of M accumulation. These studies illustrate the correspondence between pH-dependent ground-state transitions accessed by D85N and the transitions accessed by the wild-type protein following photoexcitation. We demonstrate that whole cell reflectance spectroscopy can be used to efficiently characterize the large numbers of mutants generated by engineering strategies that exploit saturation mutagenesis.
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Affiliation(s)
- Lynell C Martinez
- Department of Physiology and Biophysics and the Neurosciences Program, The University of Miami School of Medicine, Miami, FL 33101, USA
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26
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Martinez LC, Thurmond RL, Jones PG, Turner GJ. Subdomains in the F and G helices of bacteriorhodopsin regulate the conformational transitions of the reprotonation mechanism. Proteins 2002; 48:269-82. [PMID: 12112695 DOI: 10.1002/prot.10158] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have performed cysteine scanning mutagenesis of the bacteriorhodopsin mutant D85N to explore the role of individual amino acids in the conformational transitions of the reprotonation mechanism. We have used whole-cell reflectance spectroscopy to evaluate the spectral properties of the 59 mutants generated during a scan of the entire F and G helices and the intervening loop region. Cys mutants were grouped into one of six phenotypes based on the spectral changes associated with their M <--> N <--> O intermediate-state transitions. Mutations that produced similar phenotypes were found to cluster in discrete molecular domains and indicate that M, N, and O possess distinct structures and that unique molecular interactions regulate the transitions between them. The distribution of these domains suggests that 1) the extramembranous loop region is involved in the stabilization of the N and M intermediates, 2) lipid-protein interactions play a key role in the accumulation of N, and 3) the amino acid side-chain interactions in the extracellular portion of the interface between helices G and A participate in the accumulation of M.
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Affiliation(s)
- Lynell C Martinez
- Department of Physiology and Biophysics and the Neurosciences Program, University of Miami School of Medicine, Miami, Florida 33101, USA
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27
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Hatcher ME, Hu JG, Belenky M, Verdegem P, Lugtenburg J, Griffin RG, Herzfeld J. Control of the pump cycle in bacteriorhodopsin: mechanisms elucidated by solid-state NMR of the D85N mutant. Biophys J 2002; 82:1017-29. [PMID: 11806941 PMCID: PMC1301908 DOI: 10.1016/s0006-3495(02)75461-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
By varying the pH, the D85N mutant of bacteriorhodopsin provides models for several photocycle intermediates of the wild-type protein in which D85 is protonated. At pH 10.8, NMR spectra of [zeta-(15)N]lys-, [12-(13)C]retinal-, and [14,15-(13)C]retinal-labeled D85N samples indicate a deprotonated, 13-cis,15-anti chromophore. On the other hand, at neutral pH, the NMR spectra of D85N show a mixture of protonated Schiff base species similar to that seen in the wild-type protein at low pH, and more complex than the two-state mixture of 13-cis,15-syn, and all-trans isomers found in the dark-adapted wild-type protein. These results lead to several conclusions. First, the reversible titration of order in the D85N chromophore indicates that electrostatic interactions have a major influence on events in the active site. More specifically, whereas a straight chromophore is preferred when the Schiff base and residue 85 are oppositely charged, a bent chromophore is found when both the Schiff base and residue 85 are electrically neutral, even in the dark. Thus a "bent" binding pocket is formed without photoisomerization of the chromophore. On the other hand, when photoisomerization from the straight all-trans,15-anti configuration to the bent 13-cis,15-anti does occur, reciprocal thermodynamic linkage dictates that neutralization of the SB and D85 (by proton transfer from the former to the latter) will result. Second, the similarity between the chromophore chemical shifts in D85N at alkaline pH and those found previously in the M(n) intermediate of the wild-type protein indicate that the latter has a thoroughly relaxed chromophore like the subsequent N intermediate. By comparison, indications of L-like distortion are found for the chromophore of the M(o) state. Thus, chromophore strain is released in the M(o)-->M(n) transition, probably coincident with, and perhaps instrumental to, the change in the connectivity of the Schiff base from the extracellular side of the membrane to the cytoplasmic side. Because the nitrogen chemical shifts of the Schiff base indicate interaction with a hydrogen-bond donor in both M states, it is possible that a water molecule travels with the Schiff base as it switches connectivity. If so, the protein is acting as an inward-driven hydroxyl pump (analogous to halorhodopsin) rather than an outward-driven proton pump. Third, the presence of a significant C [double bond] N syn component in D85N at neutral pH suggests that rapid deprotonation of D85 is necessary at the end of the wild-type photocycle to avoid the generation of nonfunctional C [double bond] N syn species.
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Affiliation(s)
- Mary E Hatcher
- Department of Chemistry, Brandeis University, Waltham Massachusetts 02454, USA
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28
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Rouhani S, Cartailler JP, Facciotti MT, Walian P, Needleman R, Lanyi JK, Glaeser RM, Luecke H. Crystal structure of the D85S mutant of bacteriorhodopsin: model of an O-like photocycle intermediate. J Mol Biol 2001; 313:615-28. [PMID: 11676543 DOI: 10.1006/jmbi.2001.5066] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Crystal structures are reported for the D85S and D85S/F219L mutants of the light-driven proton/hydroxyl-pump bacteriorhodopsin. These mutants crystallize in the orthorhombic C222(1) spacegroup, and provide the first demonstration that monoolein-based cubic lipid phase crystallization can support the growth of well-diffracting crystals in non-hexagonal spacegroups. Both structures exhibit similar and substantial differences relative to wild-type bacteriorhodopsin, suggesting that they represent inherent features resulting from neutralization of the Schiff base counterion Asp85. We argue that these structures provide a model for the last photocycle intermediate (O) of bacteriorhodopsin, in which Asp85 is protonated, the proton release group is deprotonated, and the retinal has reisomerized to all-trans. Unlike for the M and N photointermediates, where structural changes occur mainly on the cytoplasmic side, here the large-scale changes are confined to the extracellular side. As in the M intermediate, the side-chain of Arg82 is in a downward configuration, and in addition, a pi-cloud hydrogen bond forms between Trp189 NE1 and Trp138. On the cytoplasmic side, there is increased hydration near the surface, suggesting how Asp96 might communicate with the bulk during the rise of the O intermediate.
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Affiliation(s)
- S Rouhani
- Life Sciences Division, Donner Laboratory, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA
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29
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Balashov SP. Protonation reactions and their coupling in bacteriorhodopsin. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1460:75-94. [PMID: 10984592 DOI: 10.1016/s0005-2728(00)00131-6] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Light-induced changes of the proton affinities of amino acid side groups are the driving force for proton translocation in bacteriorhodopsin. Recent progress in obtaining structures of bacteriorhodopsin and its intermediates with an increasingly higher resolution, together with functional studies utilizing mutant pigments and spectroscopic methods, have provided important information on the molecular architecture of the proton transfer pathways and the key groups involved in proton transport. In the present paper I consider mechanisms of light-induced proton release and uptake and intramolecular proton transport and mechanisms of modulation of proton affinities of key groups in the framework of these data. Special attention is given to some important aspects that have surfaced recently. These are the coupling of protonation states of groups involved in proton transport, the complex titration of the counterion to the Schiff base and its origin, the role of the transient protonation of buried groups in catalysis of the chromophore's thermal isomerization, and the relationship between proton affinities of the groups and the pH dependencies of the rate constants of the photocycle and proton transfer reactions.
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Affiliation(s)
- S P Balashov
- Center for Biophysics and Computational Biology, Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, B107 CLSL, 601 S. Goodwin Ave., 61801, Urbana, IL, USA.
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30
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Kataoka M, Kamikubo H. Structures of photointermediates and their implications for the proton pump mechanism. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1460:166-76. [PMID: 10984598 DOI: 10.1016/s0005-2728(00)00137-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
It is widely accepted that bacteriorhodopsin undergoes global conformational changes during its photocycle. In this review, the structural properties of the M and N intermediates are described in detail. Based on the clarified global conformational change, we propose a model for the molecular mechanism of the proton pump. The global structural change is suggested to be a key component in establishing vectorial proton transport.
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Affiliation(s)
- M Kataoka
- Department of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-machi, Ikoma, Nara 630-0101, Japan.
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31
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Krebs MP, Isenbarger TA. Structural determinants of purple membrane assembly. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1460:15-26. [PMID: 10984587 DOI: 10.1016/s0005-2728(00)00126-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The purple membrane is a two-dimensional crystalline lattice formed by bacteriorhodopsin and lipid molecules in the cytoplasmic membrane of Halobacterium salinarum. High-resolution structural studies, in conjunction with detailed knowledge of the lipid composition, make the purple membrane one of the best models for elucidating the forces that are responsible for the assembly and stability of integral membrane protein complexes. In this review, recent mutational efforts to identify the structural features of bacteriorhodopsin that determine its assembly in the purple membrane are discussed in the context of structural, calorimetric and reconstitution studies. Quantitative evidence is presented that interactions between transmembrane helices of neighboring bacteriorhodopsin molecules contribute to purple membrane assembly. However, other specific interactions, particularly between bacteriorhodopsin and lipid molecules, may provide the major driving force for assembly. Elucidating the molecular basis of protein-protein and protein-lipid interactions in the purple membrane may provide insights into the formation of integral membrane protein complexes in other systems.
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Affiliation(s)
- M P Krebs
- Department of Biomolecular Chemistry, University of Wisconsin Medical School, 53706-1532, Madison, WI, USA.
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32
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Birge RR, Gillespie NB, Izaguirre EW, Kusnetzow A, Lawrence AF, Singh D, Song QW, Schmidt E, Stuart JA, Seetharaman S, Wise KJ. Biomolecular Electronics: Protein-Based Associative Processors and Volumetric Memories. J Phys Chem B 1999. [DOI: 10.1021/jp991883n] [Citation(s) in RCA: 222] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert R. Birge
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Nathan B. Gillespie
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Enrique W. Izaguirre
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Anakarin Kusnetzow
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Albert F. Lawrence
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Deepak Singh
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Q. Wang Song
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Edward Schmidt
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Jeffrey A. Stuart
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Sukeerthi Seetharaman
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
| | - Kevin J. Wise
- W. M. Keck Center for Molecular Electronics and Department of Chemistry, Syracuse University, Syracuse, New York 13244
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33
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Turner GJ, Miercke LJ, Mitra AK, Stroud RM, Betlach MC, Winter-Vann A. Expression, purification, and structural characterization of the bacteriorhodopsin-aspartyl transcarbamylase fusion protein. Protein Expr Purif 1999; 17:324-38. [PMID: 10545282 DOI: 10.1006/prep.1999.1111] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We are testing a strategy for creating three-dimensional crystals of integral membrane proteins which involves the addition of a large soluble domain to the membrane protein to provide crystallization contacts. As a test of this strategy we designed a fusion between the membrane protein bacteriorhodopsin (BR) and the catalytic subunit of aspartyl transcarbamylase from Escherichia coli. The fusion protein (designated BRAT) was initially expressed in E. coli at 51 mg/liter of culture, to yield active aspartyl transcarbamylase and an unfolded bacterio-opsin (BO) component. In Halobacterium salinarum, BRAT was expressed at a yield of 7 mg/liter of culture and formed a high-density purple membrane. The visible absorption properties of BRAT were indistinguishable from those of BR, demonstrating that the fusion with aspartyl transcarbamylase had no effect on BR structure. Electron microscopy of BRAT membrane sheets showed that the fusion protein was trimeric and organized in a two-dimensional crystalline lattice similar to that in the BR purple membrane. Following solubilization and size-exclusion purification in sodium dodecyl sulfate, the BO portion of the fusion was quantitatively refolded in tetradecyl maltoside (TDM). Ultracentrifugation demonstrated that BR and BRAT-TDM mixed micelles had molecular masses of 138 and 162 kDa, respectively, with a stoichiometry of one protein per micelle. High TDM concentrations (>20 mM) were required to maintain BRAT solubility, hindering three-dimensional crystallization trials. We have demonstrated that BR can functionally accommodate massive C-terminal fusions and that these fusions may be expressed in quantities required for structural investigation in H. salinarum.
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Affiliation(s)
- G J Turner
- Department of Physiology & Biophysics, University of Miami School of Medicine, Miami, Florida, 33101, USA.
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34
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Turner GJ, Reusch R, Winter-Vann AM, Martinez L, Betlach MC. Heterologous gene expression in a membrane-protein-specific system. Protein Expr Purif 1999; 17:312-23. [PMID: 10545281 DOI: 10.1006/prep.1999.1110] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have constructed an expression system for heterologous proteins which uses the molecular machinery responsible for the high level production of bacteriorhodopsin in Halobacterium salinarum. Cloning vectors were assembled that fused sequences of the bacterio-opsin gene (bop) to coding sequences of heterologous genes and generated DNA fragments with cloning sites that permitted transfer of fused genes into H. salinarum expression vectors. Gene fusions include: (i) carboxyl-terminal-tagged bacterio-opsin; (ii) a carboxyl-terminal fusion with the catalytic subunit of the Escherichia coli aspartate transcarbamylase; (iii) the human muscarinic receptor, subtype M1; (iv) the human serotonin receptor, type 5HT2c; and (v) the yeast alpha mating factor receptor, Ste2. Characterization of the expression of these fusions revealed that the bop gene coding region contains previously undescribed molecular determinants which are critical for high level expression. For example, introduction of immunogenic and purification tag sequences into the C-terminal coding region significantly decreased bop gene mRNA and protein accumulation. The bacteriorhodopsin-aspartate transcarbamylase fusion protein was expressed at 7 mg per liter of culture, demonstrating that E. coli codon usage bias did not limit the system's potential for high level expression. The work presented describes initial efforts in the development of a novel heterologous protein expression system, which may have unique advantages for producing multiple milligram quantities of membrane-associated proteins.
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MESH Headings
- Amino Acid Sequence
- Animals
- Aspartate Carbamoyltransferase/biosynthesis
- Aspartate Carbamoyltransferase/genetics
- Aspartate Carbamoyltransferase/isolation & purification
- Bacteriorhodopsins/genetics
- Blotting, Western
- Cloning, Molecular
- DNA, Recombinant/genetics
- DNA-Binding Proteins
- Electrophoresis, Polyacrylamide Gel
- Escherichia coli/enzymology
- Gene Expression Regulation, Bacterial
- Genetic Vectors
- Halobacterium salinarum/chemistry
- Halobacterium salinarum/genetics
- Halobacterium salinarum/ultrastructure
- Humans
- Membrane Proteins/biosynthesis
- Membrane Proteins/genetics
- Membrane Proteins/isolation & purification
- Molecular Sequence Data
- Muscle Proteins
- Protein Conformation
- Purple Membrane/chemistry
- Rats
- Receptors, Mating Factor
- Receptors, Muscarinic/biosynthesis
- Receptors, Muscarinic/genetics
- Receptors, Muscarinic/isolation & purification
- Receptors, Peptide/biosynthesis
- Receptors, Peptide/genetics
- Receptors, Peptide/isolation & purification
- Receptors, Serotonin/biosynthesis
- Receptors, Serotonin/genetics
- Receptors, Serotonin/isolation & purification
- Recombinant Fusion Proteins/genetics
- Recombinant Proteins/biosynthesis
- Recombinant Proteins/genetics
- Recombinant Proteins/isolation & purification
- Transcription Factors/genetics
- Yeasts/chemistry
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Affiliation(s)
- G J Turner
- Department of Physiology & Biophysics, University of Miami School of Medicine, Miami, Florida, 33101, USA.
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35
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Kusnetzow A, Singh DL, Martin CH, Barani IJ, Birge RR. Nature of the chromophore binding site of bacteriorhodopsin: the potential role of Arg82 as a principal counterion. Biophys J 1999; 76:2370-89. [PMID: 10233056 PMCID: PMC1300211 DOI: 10.1016/s0006-3495(99)77394-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The nature of the chromophore binding site of light-adapted bacteriorhodopsin is analyzed by using modified neglect of differential overlap with partial single and double configuration interaction (MNDO-PSDCI) molecular orbital theory to interpret previously reported linear and nonlinear optical spectroscopic measurements. We conclude that in the absence of divalent metal cations in close interaction with Asp85 and Asp212, a positively charged amino acid must be present in the same vicinity. We find that models in which Arg82 is pointed upward into the chromophore binding site and directly stabilizes Asp85 and Asp212 are successful in rationalizing the observed one-photon and two-photon properties. We conclude further that a water molecule is strongly hydrogen bonded to the chromophore imine proton. The chromophore "1Bu*+" and "1Ag*-" states, despite extensive mixing, exhibit significantly different configurational character. The lowest-lying "1Bu*+" state is dominated by single excitations, whereas the second-excited "1Ag*-" state is dominated by double excitations. We can rule out the possibility of a negatively charged binding site, because such a site would produce a lowest-lying "1Ag*-" state, which is contrary to experimental observation. The possibility that Arg82 migrates toward the extracellular surface during the photocycle is examined.
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Affiliation(s)
- A Kusnetzow
- Department of Chemistry and W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244, USA
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36
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Abstract
Bacteriorhodopsin is a seven-transmembrane helical protein that contains all-trans retinal. In this light-driven pump, a reaction cycle initiated by photoisomerization to 13-cis causes translocation of a proton across the membrane. Local changes in the geometry of the protonated Schiff base and the proton acceptor Asp85, and the proton conductivities of the half channels that lead from this active site to the two membrane surfaces, interact so as to allow timely proton transfers that result in proton release on the extracellular side and proton uptake on the cytoplasmic one. The details of the steps in this photocycle, and the underlying principles that ensure unidirectionality of the movement of a proton across the protein, provide strong clues to how ion pumps function.
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Affiliation(s)
- J K Lanyi
- Department of Physiology and Biophysics, University of California, Irvine 92697-4560, USA
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37
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Baudry J, Crouzy S, Roux B, Smith JC. Simulation analysis of the retinal conformational equilibrium in dark-adapted bacteriorhodopsin. Biophys J 1999; 76:1909-17. [PMID: 10096888 PMCID: PMC1300166 DOI: 10.1016/s0006-3495(99)77349-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
In dark-adapted bacteriorhodopsin (bR) the retinal moiety populates two conformers: all-trans and (13,15)cis. Here we examine factors influencing the thermodynamic equilibrium and conformational transition between the two forms, using molecular mechanics and dynamics calculations. Adiabatic potential energy mapping indicates that whereas the twofold intrinsic torsional potentials of the C13==C14 and C15==N16 double bonds favor a sequential torsional pathway, the protein environment favors a concerted, bicycle-pedal mechanism. Which of these two pathways will actually occur in bR depends on the as yet unknown relative weight of the intrinsic and environmental effects. The free energy difference between the conformers was computed for wild-type and modified bR, using molecular dynamics simulation. In the wild-type protein the free energy of the (13,15)cis retinal form is calculated to be 1.1 kcal/mol lower than the all-trans retinal form, a value within approximately kBT of experiment. In contrast, in isolated retinal the free energy of the all-trans state is calculated to be 2.1 kcal/mol lower than (13,15)cis. The free energy differences are similar to the adiabatic potential energy differences in the various systems examined, consistent with an essentially enthalpic origin. The stabilization of the (13,15)cis form in bR relative to the isolated retinal molecule is found to originate from improved protein-protein interactions. Removing internal water molecules near the Schiff base strongly stabilizes the (13,15)cis form, whereas a double mutation that removes negative charges in the retinal pocket (Asp85 to Ala; Asp212 to Ala) has the opposite effect.
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Affiliation(s)
- J Baudry
- Section de Biophysique des Protéines et des Membranes, DBCM, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
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38
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Back photoreaction from intermediate M of bacteriorhodopsin photocycle. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1999. [DOI: 10.1016/s1011-1344(98)00220-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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39
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Ganea C, Tittor J, Bamberg E, Oesterhelt D. Chloride- and pH-dependent proton transport by BR mutant D85N. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1368:84-96. [PMID: 9459587 DOI: 10.1016/s0005-2736(97)00173-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Photocurrents from purple membrane suspensions of D85N BR mutant adsorbed to planar lipid membranes (BLM) were recorded under yellow (lambda > 515 nm), blue (360 nm < lambda < 420 nm) and white (lambda > 360 nm) light. The pH dependence of the transient and stationary currents was studied in the range from 4.5 to 10.5. The outwardly directed stationary currents in yellow and blue light indicate the presence of a proton pumping activity, dependent on the pH of the sample, in the same direction as in the wild-type. The inwardly directed currents in white light, due to an inverse proton translocation, in a two-photon process, show a pH dependence as well. The stationary currents in blue and white light are drastically increased in the presence of azide, but not in yellow light. The concentration dependence of the currents on azide indicates binding of azide to the protein. In the presence of 1 M sodium chloride, the stationary proton currents in yellow light show an increase by a factor of 25 at pH 5.5. On addition of 50 mM azide, the stationary current in yellow light decreases again, possibly by competition between azide and chloride for a common binding site. The observed transport modes are discussed in the framework of the recently published IST model for ion translocation by retinal proteins [U. Haupts et al., Biochemistry 36 (1997) 2-7].
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Affiliation(s)
- C Ganea
- Max-Planck-Institut für Biophysik, Frankfurt, Germany.
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40
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Tittor J, Haupts U, Haupts C, Oesterhelt D, Becker A, Bamberg E. Chloride and proton transport in bacteriorhodopsin mutant D85T: different modes of ion translocation in a retinal protein. J Mol Biol 1997; 271:405-16. [PMID: 9268668 DOI: 10.1006/jmbi.1997.1204] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Replacement of aspartate 85 (D85) in bacteriorhodopsin (BR) by threonine but not be asparagine creates at pH<7 an anion-binding site in the molecular similar to that in chloride pump halorhodopsin. Binding of various anions to BR-D85T causes a blue shift of the absorption maximum by maximally 57 nm. Connected to this color change is a change in the absorption difference spectrum of the initial state and the longest living photo intermediate from a positive difference maximum at 460 nm in the absence of transported anions to one at 630 nm in their presence. Increasing anion concentration cause decreasing decay times of this intermediate. At physiological pH, BR-D85T but not BR-D85N transports chloride ions inward in green light, protons outward in blue or green light and protons inward in white light (directions refer to the intact cell). The proton movements are observable also in BR-D85N. Thus, creation of an anion-binding site in BR is responsible for chloride transport and introduction of anion-dependent spectroscopic properties at physiological pH. The different transport modes are explained with the help of the recently proposed IST model, which states that after light-induced isomerization of the retinal an ion transfer step and an accessibility change of the active site follow. The latter two steps occur independently. In order to complete the cyclic event, the accessibility change, ion transfer and isomerization state have to be reversed. The relative rates of accessibility changes and ion transfer steps define ultimately the vectoriality of ion transfers. All transport modes described here for the same molecule can satisfactorily be described in the framework of this general concept.
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Affiliation(s)
- J Tittor
- Max-Planck-Institut für Biochemie, Martinsried, D82152, Germany
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41
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Brown LS, Kamikubo H, Zimányi L, Kataoka M, Tokunaga F, Verdegem P, Lugtenburg J, Lanyi JK. A local electrostatic change is the cause of the large-scale protein conformation shift in bacteriorhodopsin. Proc Natl Acad Sci U S A 1997; 94:5040-4. [PMID: 9144186 PMCID: PMC24627 DOI: 10.1073/pnas.94.10.5040] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
During light-driven proton transport bacteriorhodopsin shuttles between two protein conformations. A large-scale structural change similar to that in the photochemical cycle is produced in the D85N mutant upon raising the pH, even without illumination. We report here that (i) the pKa values for the change in crystallographic parameters and for deprotonation of the retinal Schiff base are the same, (ii) the retinal isomeric configuration is nearly unaffected by the protein conformation, and (iii) preventing rotation of the C13-C14 double bond by replacing the retinal with an all-trans locked analogue makes little difference to the Schiff base pKa. We conclude that the direct cause of the conformational shift is destabilization of the structure upon loss of interaction of the positively charged Schiff base with anionic residues that form its counter-ion.
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Affiliation(s)
- L S Brown
- Department of Physiology & Biophysics, University of California, Irvine, CA 92697-4560, USA
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42
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Roepe PD, Wei LY, Hoffman MM, Fritz F. Altered drug translocation mediated by the MDR protein: direct, indirect, or both? J Bioenerg Biomembr 1996; 28:541-55. [PMID: 8953386 DOI: 10.1007/bf02110444] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Overexpression of the MDR protein, or p-glycoprotein (p-GP), in cells leads to decreased initial rates of accumulation and altered intracellular retention of chemotherapeutic drugs and a variety of other compounds. Thus, increased expression of the protein is related to increased drug resistance. Since several homologues of the MDR protein (CRP, ItpGPA, PDR5, sapABCDF) are also involved in conferring drug resistance phenomena in microorganisms, elucidating the function of the MDR protein at a molecular level will have important general applications. Although MDR protein function has been studied for nearly 20 years, interpretation of most data is complicated by the drug-selection conditions used to create model MDR cell lines. Precisely what level of resistance to particular drugs is conferred by a given amount of MDR protein, as well as a variety of other critical issues, are not yet resolved. Data from a number of laboratories has been gathered in support of at least four different models for the MDR protein. One model is that the protein uses the energy released from ATP hydrolysis to directly translocate drugs out of cells in some fashion. Another is that MDR protein overexpression perturbs electrical membrane potential (delta psi) and/or intracellular pH (pHi) and thereby indirectly alters translocation and intracellular retention of hydrophobic drugs that are cationic, weakly basic, and/or that react with intracellular targets in a pHi or delta psi-dependent manner. A third model proposes that the protein alternates between drug pump and Cl- channel (or channel regulator) conformations, implying that both direct and indirect mechanisms of altered drug translocation may be catalyzed by MDR protein. A fourth is that the protein acts as an ATP channel. Our recent work has tested predictions of these models via kinetic analysis of drug transport and single-cell photometry analysis of pHi, delta psi, and volume regulation in novel MDR and CFTR transfectants that have not been exposed to chemotherapeutic drugs prior to analysis. This paper reviews these data and previous work from other laboratories, as well as relevant transport physiology concepts, and summarizes how they either support or contradict the different models for MDR protein function.
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Affiliation(s)
- P D Roepe
- Molecular Pharmacology and Therapeutics Program, Raymond & Beverly Sackler Foundation Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York, USA
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43
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Logunov I, Schulten K. Quantum Chemistry: Molecular Dynamics Study of the Dark-Adaptation Process in Bacteriorhodopsin. J Am Chem Soc 1996. [DOI: 10.1021/ja953091m] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ilya Logunov
- Contribution from the Beckman Institute and Departments of Chemistry and Physics, University of Illinois at UrbanaChampaign, 405 North Matthews Avenue, Urbana, Illinois 61801
| | - Klaus Schulten
- Contribution from the Beckman Institute and Departments of Chemistry and Physics, University of Illinois at UrbanaChampaign, 405 North Matthews Avenue, Urbana, Illinois 61801
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44
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Balashov SP, Imasheva ES, Govindjee R, Sheves M, Ebrey TG. Evidence that aspartate-85 has a higher pK(a) in all-trans than in 13-cisbacteriorhodopsin. Biophys J 1996; 71:1973-84. [PMID: 8889171 PMCID: PMC1233663 DOI: 10.1016/s0006-3495(96)79395-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Three experimental observations indicate that the pK(a) of the purple-to-blue transition (the pK(a) of Asp-85) is higher for all-trans-bR(1) than for 13-cis-bR. First, light adaptation of bacteriorhodopsin (bR) at pHs near the pK(a) of Asp-85 causes an increase in the fraction of the blue membrane present. This transformation is reversible in the dark. Second, the pK(a) of the purple-to-blue transition in the dark is lower than that in the light-adapted bR (pK(a)(DA) = 3.5, pK(a)(LA) = 3.8 in 10 microM K(2)SO(4)). Third, the equilibrium fractions of 13-cis and all-trans isomers are pH dependent; the fraction of all-trans-bR increases upon formation of the blue membrane. Based on the conclusion that thermal all-trans <=> 13-cis isomerization occurs in the blue membrane rather than in the purple, we have developed a simple model that accounts for all three observations. From the fit of experimental data we estimate that the pK(a) of Asp-85 in 13-cis-bR is 0.5 +/- 0.1 pK(a) unit less than the pK(a) of all-trans-bR. Thus in 10 microM K(2)SO(4), pK(a)(c) = 3.3, whereas pK(a)(t) = 3.8.
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Affiliation(s)
- S P Balashov
- Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign 61801, USA
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45
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Nilsson A, Rath P, Olejnik J, Coleman M, Rothschild KJ. Protein conformational changes during the bacteriorhodopsin photocycle. A Fourier transform infrared/resonance Raman study of the alkaline form of the mutant Asp-85-->Asn. J Biol Chem 1995; 270:29746-51. [PMID: 8530365 DOI: 10.1074/jbc.270.50.29746] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Bacteriorhodopsin is a light-driven proton pump, which undergoes a photocycle consisting of several distinct intermediates. Previous studies have established that the M-->N step of this photocycle involves a major conformational change of membrane embedded alpha-helices. In order to further investigate this conformational change, we have studied the photocycle of the high pH form of the mutant Asp-85-->Asn (D85Nalk). In contrast to wild type bacteriorhodopsin, D85Nalk has a deprotonated Schiff base and a blue-shifted absorption near 410 nm, yet it still transports protons in the same direction as wild type bacteriorhodopsin (Tittor, J., Schweiger, U., Oesterhelt, D. and Bamberg, E. (1994) Biophys. J., 67, 1682-1690). Resonance Raman spectroscopy of D85Nalk and D85Nalk regenerated with retinal labeled at the C-15 position with deuterium reveals the existence of an all-trans configuration of the chromophore. Fourier transform infrared difference spectroscopy shows that the photocycle of this light-adapted form involves similar events as the wild type bacteriorhodopsin photocycle including the M-->N protein conformational change. These results help to explain the ability of D85Nalk to transport protons and demonstrate that the M-->N conformational change can occur even in the photocycle of an unprotonated Schiff base form of bacteriorhodopsin.
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Affiliation(s)
- A Nilsson
- Physics Department, Boston University, Massachusetts 02215, USA
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46
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Dickopf S, Alexiev U, Krebs MP, Otto H, Mollaaghababa R, Khorana HG, Heyn MP. Proton transport by a bacteriorhodopsin mutant, aspartic acid-85-->asparagine, initiated in the unprotonated Schiff base state. Proc Natl Acad Sci U S A 1995; 92:11519-23. [PMID: 8524795 PMCID: PMC40433 DOI: 10.1073/pnas.92.25.11519] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
At alkaline pH the bacteriorhodopsin mutant D85N, with aspartic acid-85 replaced by asparagine, is in a yellow form (lambda max approximately 405 nm) with a deprotonated Schiff base. This state resembles the M intermediate of the wild-type photocycle. We used time-resolved methods to show that this yellow form of D85N, which has an initially unprotonated Schiff base and which lacks the proton acceptor Asp-85, transports protons in the same direction as wild type when excited by 400-nm flashes. Photoexcitation leads in several milliseconds to the formation of blue (630 nm) and purple (580 nm) intermediates with a protonated Schiff base, which decay in tens of seconds to the initial state (400 nm). Experiments with pH indicator dyes show that at pH 7, 8, and 9, proton uptake occurs in about 5-10 ms and precedes the slow release (seconds). Photovoltage measurements reveal that the direction of proton movement is from the cytoplasmic to the extracellular side with major components on the millisecond and second time scales. The slowest electrical component could be observed in the presence of azide, which accelerates the return of the blue intermediate to the initial yellow state. Transport thus occurs in two steps. In the first step (milliseconds), the Schiff base is protonated by proton uptake from the cytoplasmic side, thereby forming the blue state. From the pH dependence of the amplitudes of the electrical and photocycle signals, we conclude that this reaction proceeds in a similar way as in wild type--i.e., via the internal proton donor Asp-96. In the second step (seconds) the Schiff base deprotonates, releasing the proton to the extracellular side.
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Affiliation(s)
- S Dickopf
- Department of Physics, Freie Universität Berlin, Germany
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47
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Moltke S, Krebs MP, Mollaaghababa R, Khorana HG, Heyn MP. Intramolecular charge transfer in the bacteriorhodopsin mutants Asp85-->Asn and Asp212-->Asn: effects of pH and anions. Biophys J 1995; 69:2074-83. [PMID: 8580351 PMCID: PMC1236441 DOI: 10.1016/s0006-3495(95)80078-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The photovoltage kinetics of the bacteriorhodopsin mutants Asp212-->Asn and Asp85-->Asn after excitation at 580 nm have been investigated in the pH range from 0 to 11. With the mutant Asp85-->Asn (D85N) at pH 7 no net charge translocation is observed and the signal is the same, both in the presence of Cl- (150 mM) and in its absence (75 mM SO4(2-)). Under both conditions the color of the pigment is blue (lambda max = 615 nm). The time course of the photovoltage kinetics is similar to that of the acid-blue form of wild-type, except that an additional transient charge motion occurs with time constants of 60 microseconds and 1.3 ms, indicating the transient deprotonation and reprotonation of an unknown group to and from the extracellular side of the membrane. It is suggested that this is the group XH, which is responsible for proton release in wild-type. At pH 1, the photovoltage signal of D85N changes upon the addition of Cl- from that characteristic for the acid-blue state of wild-type to that characteristic for the acid-purple state. Therefore, the protonation of the group at position at 85 is necessary, but not sufficient for the chloride-binding. At pH 11, well above the pKa of the Schiff base, there is a mixture of "M-like" and "N-like" states. Net proton transport in the same direction as in wild-type is restored in D85N from this N-like state. With the mutant Asp212-->Asn (D212N), time-resolved photovoltage measurements show that in the absence of halide ions the signal is similar to that of the acid-blue form of wild-type and that no net charge translocation occurs in the entire pH range from 0 to 11. Upon addition of Cl- in the pH range from 3.8 to 7.2 the color of the pigment returns to purple and the photovoltage experiments indicate that net proton pumping is restored. However, this Cl(-)-induced activation of net charge-transport in D212N is only partial. Outside this pH range, no net charge transport is observed even in the presence of chloride, and the photovoltage shows the same chloride-dependent features as those accompanying the acid-blue to acid-purple transition of the wild-type.
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Affiliation(s)
- S Moltke
- Department of Physics, Freie Universität Berlin, Germany
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48
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Abstract
Recent studies of the photochemistry of wild type and mutant bacteriorhodopsins, their proton release and uptake kinetics, and their X-ray diffraction structure have suggested a hypothesis for the way energy is coupled in this light-driven proton pump. The first and critical step in converting light energy to a vectorial proton potential is the transfer of the Schiff base proton to D85 which causes dissociation of the Schiff base-counterion complex. Removal of this primarily coulombic interaction destabilizes the protein structure, and results in transition to an alternative conformation in which the two proton conduction pathways between the active site and the membrane surfaces are reorganized. Recovery of the initial charge state of the Schiff base and D85 must therefore occur through a series of unidirectional proton transfers that create a transmembrane electrochemical proton gradient. Passage of the transported proton through the two peripheral protein domains appears to utilize hydrogen bonded networks containing aspartate, arginine and bound water. This kind of mutual interaction between the active site and the protein conformation that determines the conductive pathways to the two membrane surfaces may have relevance to ion pumps in general.
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Affiliation(s)
- J K Lanyi
- Department of Physiology and Biophysics, University of California, Irvine, CA 92717, USA
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49
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Haupts U, Haupts C, Oesterhelt D. The photoreceptor sensory rhodopsin I as a two-photon-driven proton pump. Proc Natl Acad Sci U S A 1995; 92:3834-8. [PMID: 11607531 PMCID: PMC42056 DOI: 10.1073/pnas.92.9.3834] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proton translocation experiments with intact cells of Halobacterium salinarium overproducing sensory rhodopsin I (SRI) revealed transport activity of SRI in a two-photon process. The vectoriality of proton translocation depends on pH, being outwardly directed above, and inwardly directed below, pH 5.7. Activation of the transport cycle requires excitation of the initial dark state of SRI, SRI590, to form the intermediate SRI380. Action spectra identify the photocycle intermediates SRI380 and SRI520 as the two photochemically reactive species in the outwardly directed transport process. As shown by flash photolysis experiments, SRI520 undergoes a so-far unknown photochemical reaction to SRI380 with a half-time of <200 micros. Mutation of SRI residue Asp-76, the residue which is equivalent to the proton acceptor Asp-85 in bacteriorhodopsin, to asparagine leads to inactivation of proton translocation. This demonstrates that the underlying mechanisms of proton transport in both retinal proteins share similar features. However, SRI is to our knowledge the first case where photochemical reactions between two thermally unstable photoproducts of a retinal protein constitute a catalytic ion transport cycle.
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Affiliation(s)
- U Haupts
- Max-Planck-Institut für Biochemie, Martinsried, Germany
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50
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Gergely C, Ganea C, Száraz S, Váró G. Charge motions studied in the bacteriorhodopsin mutants D85N and D212N. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1995. [DOI: 10.1016/1011-1344(94)07057-u] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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