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Bondar AN, Baudry J, Suhai S, Fischer S, Smith JC. Key Role of Active-Site Water Molecules in Bacteriorhodopsin Proton-Transfer Reactions. J Phys Chem B 2008; 112:14729-41. [DOI: 10.1021/jp801916f] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ana-Nicoleta Bondar
- Computational Molecular Biophysics, IWR, University of Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany, Molecular Biophysics Department, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany, University of California at Irvine, Department of Physiology and Biophysics and the Center for Biomembrane Systems, Med. Sci. I, D-374, Irvine, California 92697-4560, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge
| | - Jerome Baudry
- Computational Molecular Biophysics, IWR, University of Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany, Molecular Biophysics Department, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany, University of California at Irvine, Department of Physiology and Biophysics and the Center for Biomembrane Systems, Med. Sci. I, D-374, Irvine, California 92697-4560, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge
| | - Sándor Suhai
- Computational Molecular Biophysics, IWR, University of Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany, Molecular Biophysics Department, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany, University of California at Irvine, Department of Physiology and Biophysics and the Center for Biomembrane Systems, Med. Sci. I, D-374, Irvine, California 92697-4560, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge
| | - Stefan Fischer
- Computational Molecular Biophysics, IWR, University of Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany, Molecular Biophysics Department, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany, University of California at Irvine, Department of Physiology and Biophysics and the Center for Biomembrane Systems, Med. Sci. I, D-374, Irvine, California 92697-4560, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge
| | - Jeremy C. Smith
- Computational Molecular Biophysics, IWR, University of Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany, Molecular Biophysics Department, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany, University of California at Irvine, Department of Physiology and Biophysics and the Center for Biomembrane Systems, Med. Sci. I, D-374, Irvine, California 92697-4560, University of Tennessee/Oak Ridge National Laboratory Center for Molecular Biophysics, Oak Ridge
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102
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Morgan JE, Vakkasoglu AS, Lugtenburg J, Gennis RB, Maeda A. Structural changes due to the deprotonation of the proton release group in the M-photointermediate of bacteriorhodopsin as revealed by time-resolved FTIR spectroscopy. Biochemistry 2008; 47:11598-605. [PMID: 18837559 DOI: 10.1021/bi801405v] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
One of the steps in the proton pumping cycle of bacteriorhodopsin (BR) is the release of a proton from the proton-release group (PRG) on the extracellular side of the Schiff base. This proton release takes place shortly after deprotonation of the Schiff base (L-to-M transition) and results in an increase in the pKa of Asp85, which is a crucial mechanistic step for one-way proton transfer for the entire photocycle. Deprotonation of the PRG can also be brought about without photoactivation, by raising the pH of the enzyme (pKa of PRG; approximately 9). Thus, comparison of the FTIR difference spectrum for formation of the M intermediate (M minus initial unphotolyzed BR state) at pH 7 to the corresponding spectrum generated at pH 10 may reveal structural changes specifically associated with deprotonation of the PRG. Vibrational bands of BR that change upon M formation are distributed across a broad region between 2120 and 1685 cm(-1). This broad band is made up of two parts. The band above 1780 cm(-1), which is insensitive to C15-deuteration of the retinal, may be due to a proton delocalized in the PRG. The band between 1725 and 1685 cm(-1), on the lower frequency side of the broad band, is sensitive to C15-deuteration. This band may arise from transition dipole coupling of the vibrations of backbone carbonyl groups in helix G with the side chain of Tyr57 and with the C15H of the Schiff base. In M, these broad bands are abolished, and the 3657 cm(-1) band, which is due to the disruption of the hydrogen bonding of a water molecule, probably with Arg82, appears. Loss of the interaction of the backbone carbonyl groups in helix G with Tyr57 and the Schiff base, and separation of Tyr57 from Arg82, may be causes of these spectral changes, leading to the stabilization of the protonated Asp85 in M.
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Affiliation(s)
- Joel E Morgan
- Department of Biology, Center for Biotechnology and Interdisciplinary Studies, Room 2137, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180, USA
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103
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Mitchell-Koch KR, Thompson WH. Infrared spectra of a model phenol-amine proton transfer complex in nanoconfined CH3Cl. J Phys Chem B 2008; 112:7448-59. [PMID: 18517239 DOI: 10.1021/jp076714e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The vibrational spectra of a model phenol-amine proton transfer complex dissolved in CH3Cl solvent confined in a 12 A radius spherical hydrophobic cavity were calculated using mixed quantum-classical molecular dynamics simulations. The reaction free energy of the proton transfer complex was varied in order to explore the contributions to the vibrational absorption band from product and reactant species. The vibrational spectra of the model proton transfer complex resulted in motionally narrowed spectral linewidths with two distinct peaks for products and reactants in cases where the system undergoes chemical exchange. It was found that the n=1 and n=2 vibrational excited states combine to form diabatic states such that the spectra have contributions from both n=0 --> n=1 and n=0 --> n=2 transitions. A strong relationship between the instantaneous vibrational frequency and a collective solvent coordinate was found that assists in understanding the origin of the spectral features.
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104
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Protons and how they are transported by proton pumps. Pflugers Arch 2008; 457:573-9. [DOI: 10.1007/s00424-008-0503-8] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Revised: 03/17/2008] [Accepted: 03/21/2008] [Indexed: 12/01/2022]
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105
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106
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Kurtz I, Kraut J, Ornekian V, Nguyen MK. Acid-base analysis: a critique of the Stewart and bicarbonate-centered approaches. Am J Physiol Renal Physiol 2008; 294:F1009-31. [PMID: 18184741 DOI: 10.1152/ajprenal.00475.2007] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
When approaching the analysis of disorders of acid-base balance, physical chemists, physiologists, and clinicians, tend to focus on different aspects of the relevant phenomenology. The physical chemist focuses on a quantitative understanding of proton hydration and aqueous proton transfer reactions that alter the acidity of a given solution. The physiologist focuses on molecular, cellular, and whole organ transport processes that modulate the acidity of a given body fluid compartment. The clinician emphasizes the diagnosis, clinical causes, and most appropriate treatment of acid-base disturbances. Historically, two different conceptual frameworks have evolved among clinicians and physiologists for interpreting acid-base phenomena. The traditional or bicarbonate-centered framework relies quantitatively on the Henderson-Hasselbalch equation, whereas the Stewart or strong ion approach utilizes either the original Stewart equation or its simplified version derived by Constable. In this review, the concepts underlying the bicarbonate-centered and Stewart formulations are analyzed in detail, emphasizing the differences in how each approach characterizes acid-base phenomenology at the molecular level, tissue level, and in the clinical realm. A quantitative comparison of the equations that are currently used in the literature to calculate H+concentration ([H+]) is included to clear up some of the misconceptions that currently exist in this area. Our analysis demonstrates that while the principle of electroneutrality plays a central role in the strong ion formulation, electroneutrality mechanistically does not dictate a specific [H+], and the strong ion and bicarbonate-centered approaches are quantitatively identical even in the presence of nonbicarbonate buffers. Finally, our analysis indicates that the bicarbonate-centered approach utilizing the Henderson-Hasselbalch equation is a mechanistic formulation that reflects the underlying acid-base phenomenology.
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107
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Braun-Sand S, Sharma PK, Chu ZT, Pisliakov AV, Warshel A. The energetics of the primary proton transfer in bacteriorhodopsin revisited: it is a sequential light-induced charge separation after all. BIOCHIMICA ET BIOPHYSICA ACTA 2008; 1777:441-52. [PMID: 18387356 PMCID: PMC2443747 DOI: 10.1016/j.bbabio.2008.03.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2007] [Revised: 02/29/2008] [Accepted: 03/03/2008] [Indexed: 11/26/2022]
Abstract
The light-induced proton transport in bacteriorhodopsin has been considered as a model for other light-induced proton pumps. However, the exact nature of this process is still unclear. For example, it is not entirely clear what the driving force of the initial proton transfer is and, in particular, whether it reflects electrostatic forces or other effects. The present work simulates the primary proton transfer (PT) by a specialized combination of the EVB and the QCFF/PI methods. This combination allows us to obtain sufficient sampling and a quantitative free energy profile for the PT at different protein configurations. The calculated profiles provide new insight about energetics of the primary PT and its coupling to the protein conformational changes. Our finding confirms the tentative analysis of an earlier work (A. Warshel, Conversion of light energy to electrostatic energy in the proton pump of Halobacterium halobium, Photochem. Photobiol. 30 (1979) 285-290) and determines that the overall PT process is driven by the energetics of the charge separation between the Schiff base and its counterion Asp85. Apparently, the light-induced relaxation of the steric energy of the chromophore leads to an increase in the ion-pair distance, and this drives the PT process. Our use of the linear response approximation allows us to estimate the change in the protein conformational energy and provides the first computational description of the coupling between the protein structural changes and the PT process. It is also found that the PT is not driven by twist-modulated changes of the Schiff base's pKa, changes in the hydrogen bond directionality, or other non-electrostatic effects. Overall, based on a consistent use of structural information as the starting point for converging free energy calculations, we conclude that the primary event should be described as a light-induced formation of an unstable ground state, whose relaxation leads to charge separation and to the destabilization of the ion-pair state. This provides the driving force for the subsequent PT steps.
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Affiliation(s)
- Sonja Braun-Sand
- Department of Chemistry, University of Southern California, 418 SGM Building, 3620 McClintock Avenue, Los Angeles, CA 90089-1062, USA
- Department of Chemistry, University of Colorado at Colorado Springs (UCCS), Colorado Springs, CO 80918
| | - Pankaz K. Sharma
- Department of Chemistry, University of Southern California, 418 SGM Building, 3620 McClintock Avenue, Los Angeles, CA 90089-1062, USA
| | - Zhen T. Chu
- Department of Chemistry, University of Southern California, 418 SGM Building, 3620 McClintock Avenue, Los Angeles, CA 90089-1062, USA
| | - Andrei V. Pisliakov
- Department of Chemistry, University of Southern California, 418 SGM Building, 3620 McClintock Avenue, Los Angeles, CA 90089-1062, USA
| | - Arieh Warshel
- Department of Chemistry, University of Southern California, 418 SGM Building, 3620 McClintock Avenue, Los Angeles, CA 90089-1062, USA
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108
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Iftimie R, Thomas V, Plessis S, Marchand P, Ayotte P. Spectral Signatures and Molecular Origin of Acid Dissociation Intermediates. J Am Chem Soc 2008; 130:5901-7. [DOI: 10.1021/ja077846o] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Radu Iftimie
- Départment de Chimie, Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C3J7, Canada, and Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke J1K2R1, Canada
| | - Vibin Thomas
- Départment de Chimie, Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C3J7, Canada, and Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke J1K2R1, Canada
| | - Sylvain Plessis
- Départment de Chimie, Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C3J7, Canada, and Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke J1K2R1, Canada
| | - Patrick Marchand
- Départment de Chimie, Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C3J7, Canada, and Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke J1K2R1, Canada
| | - Patrick Ayotte
- Départment de Chimie, Université de Montréal, CP 6128, succursale Centre-Ville, Montréal H3C3J7, Canada, and Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke J1K2R1, Canada
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109
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Yu H, Cui Q. The vibrational spectra of protonated water clusters: A benchmark for self-consistent-charge density-functional tight binding. J Chem Phys 2007; 127:234504. [DOI: 10.1063/1.2806992] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
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110
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Affiliation(s)
- Philip Ball
- Nature, 4-6 Crinan Street, London N1 9XW, U.K
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111
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Abstract
A mixed quantum/classical investigation of the dynamical magnetostructural properties, that is, "magnetodynamics," of oxidized Anabaena PCC7119 ferredoxin is carried out at room temperature in two distinct conformational states. This protein hosts a [2Fe-2S] cluster in which two iron centers are antiferromagnetically coupled to an overall low-spin electronic ground state that has a genuine multireference character. To study the magnetodynamics of this prosthetic group, an approximate spin projection method is formulated in the framework of density functional theory that allows for multideterminant ab initio molecular dynamics simulations to be carried out efficiently. By using this scheme, the influence of both thermal fluctuations and conformational motion on the structure of the [2Fe-2S] cluster and on the dynamics of the antiferromagnetic coupling constant, J(t), has been investigated. In addition to demonstrating how sensitively the shape of the [2Fe-2S] core itself is affected by hydrogen bonding, the analyses reveal a complex dynamical coupling of J to both local vibrations and large-amplitude motion. It is shown that this interplay can be understood in terms of specific vibrational modes and distinct hydrogen-bonding patterns between the iron-sulfur cluster and the protein backbone, respectively. This implies going beyond the Goodenough-Kanamori rules for angular magnetostructural correlations of oxidized iron-sulfur prosthetic groups.
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112
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Gu W, Helms V. Different Protonation Equilibria of 4-Methylimidazole and Acetic Acid. Chemphyschem 2007; 8:2445-51. [DOI: 10.1002/cphc.200700442] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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113
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Asmis K, Yang Y, Santambrogio G, Brümmer M, Roscioli J, McCunn L, Johnson M, Kühn O. Gasphasen-Infrarotspektroskopie und mehrdimensionale quantenmechanische Rechnungen zum protonierten Ammoniakdimer N2H7+. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200702607] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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114
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Asmis K, Yang Y, Santambrogio G, Brümmer M, Roscioli J, McCunn L, Johnson M, Kühn O. Gas-Phase Infrared Spectroscopy and Multidimensional Quantum Calculations of the Protonated Ammonia Dimer N2H7+. Angew Chem Int Ed Engl 2007; 46:8691-4. [DOI: 10.1002/anie.200702607] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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115
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Masia M, Forbert H, Marx D. Connecting Structure to Infrared Spectra of Molecular and Autodissociated HCl−Water Aggregates. J Phys Chem A 2007; 111:12181-91. [DOI: 10.1021/jp0740494] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Marco Masia
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - Harald Forbert
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - Dominik Marx
- Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
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116
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Klare JP, Chizhov I, Engelhard M. Microbial rhodopsins: scaffolds for ion pumps, channels, and sensors. Results Probl Cell Differ 2007; 45:73-122. [PMID: 17898961 DOI: 10.1007/400_2007_041] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Microbial rhodopsins have been intensively researched for the last three decades. Since the discovery of bacteriorhodopsin, the scope of microbial rhodopsins has been considerably extended, not only in view of the large number of family members, but also their functional properties as pumps, sensors, and channels. In this review, we give a short overview of old and newly discovered microbial rhodopsins, the mechanism of signal transfer and ion transfer, and we discuss structural and mechanistic aspects of phototaxis.
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Affiliation(s)
- Johann P Klare
- Fachbereich Physik, University Osnabrück, Barbarastrasse 7, 49069, Osnabrück, Germany
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