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Intramolekulare Proteindynamik untersucht mit zeitaufgelöster Fourier Transform Infrarot-Differenzspektroskopie. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/bbpc.198800244] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Janovak L, Tallósy S, Sztakó M, Deak A, Bitó T, Buzas N, Bartfai G, Dékany I. Synthesis of pH-sensitive copolymer thin solid films embedded with silver nanoparticles for controlled release and their fungicide properties. J Drug Deliv Sci Technol 2014. [DOI: 10.1016/s1773-2247(14)50129-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Friedrich T, Geibel S, Kalmbach R, Chizhov I, Ataka K, Heberle J, Engelhard M, Bamberg E. Proteorhodopsin is a light-driven proton pump with variable vectoriality. J Mol Biol 2002; 321:821-38. [PMID: 12206764 DOI: 10.1016/s0022-2836(02)00696-4] [Citation(s) in RCA: 190] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Proteorhodopsin, a homologue of archaeal bacteriorhodopsin (BR), belongs to a newly identified family of retinal proteins from marine bacteria, which could play an important role in the energy balance of the biosphere. We cloned the cDNA sequence of proteorhodopsin by chemical gene synthesis, expressed the protein in Escherichia coli cells, purified and reconstituted the protein in its functional active state. The photocycle characteristics were determined by time-resolved absorption and Fourier transform infrared (FT-IR) spectroscopy. The pH-dependence of the absorption spectrum indicates that the pK(a) of the primary acceptor of the Schiff base proton (Asp97) is 7.68. Generally, the photocycle of proteorhodopsin is similar to that of BR, although an L-like photocycle intermediate was not detectable. Whereas at pH>7 an M-like intermediate is formed upon illumination, at pH 5 no M-like intermediate could be detected. As the photocycle kinetics do not change between the acidic and alkaline state of proteorhodopsin, the only difference between these two forms is the protonation status of Asp97. This is corroborated by time-resolved FT-IR spectroscopy, which demonstrates that proton transfer from the retinal Schiff base to Asp97 is observed at alkaline pH, but the other vibrational changes are essentially pH-independent.After reconstitution into proteoliposomes, light-induced proton currents of proteorhodopsin were measured in a compound membrane system where proteoliposomes were adsorbed to planar lipid bilayers. Our results show that proteorhodopsin is a light-driven proton pump with characteristics similar to those of BR at alkaline pH. However, at acidic pH, the direction of proton pumping is inverted. Complementary experiments were carried out on proteorhodopsin expressed heterologously in Xenopus laevis oocytes under voltage clamp conditions. The following results were obtained. (1) At alkaline pH, proteorhodopsin mediates outwardly directed proton pumping like BR. (2) The direction of proton pumping can be inverted, when Asp97 is protonated. (3) The current can be inverted by changes of the polarity of the applied voltage. (4) The light intensity-dependence of the photocurrents leads to the conclusion that the alkaline form of proteorhodopsin shows efficient proton pumping after sequential excitation by two photons.
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Affiliation(s)
- Thomas Friedrich
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry, Kennedyallee 70, D-60596 Frankfurt am Main, Germany
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Mehler EL, Fuxreiter M, Simon I, Garcia-Moreno EB. The role of hydrophobic microenvironments in modulating pKa shifts in proteins. Proteins 2002; 48:283-92. [PMID: 12112696 DOI: 10.1002/prot.10153] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The screened Coulomb potential (SCP) method, combined with a quantitative description of the microenvironments around titratable groups, based on the Hydrophobic Fragmental Constants developed by Rekker, has been applied to calculate the pK(a) values of groups embedded in extremely hydrophobic microenvironments in proteins. This type of microenvironment is not common; but constitutes a small class, where the protein's architecture has evolved to lend special properties to the embedded residue. They are of significant interest because they are frequently important in catalysis and in proton and electron transfer reactions. In the SCP treatment these special cases are treated locally and therefore do not affect the accuracy of the pK(a) values calculated for other residues in less hydrophobic environments. Here the calibration of the algorithm is extended with the help of earlier results from lysozyme and of three mutants of staphylococcal nuclease (SNase) that were specially designed to measure the energetics of ionization of titratable groups buried in extremely hydrophobic microenvironments. The calibrated algorithm was subsequently applied to a fourth mutant of SNase and then to a very large dimeric amine oxidase of 1284 residues, where 334 are titratable. The observed pK(a) shifts of the buried residues are large (up to 4.7 pK units), and all cases are well reproduced by the calculations with a root mean square error of 0.22. These results support the hypothesis that protein electrostatics can only be described correctly and self-consistently if the inherent heterogeneity of these systems is properly accounted for.
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Affiliation(s)
- E L Mehler
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029, USA.
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Masthay MB, Sammeth DM, Helvenston MC, Buckman CB, Li W, Cde-Baca MJ, Kofron JT. The laser-induced blue state of bacteriorhodopsin: mechanistic and color regulatory roles of protein-protein interactions, protein-lipid interactions, and metal ions. J Am Chem Soc 2002; 124:3418-30. [PMID: 11916428 DOI: 10.1021/ja010116a] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In this paper we characterize the mechanistic roles of the crystalline purple membrane (PM) lattice, the earliest bacteriorhodopsin (BR) photocycle intermediates, and divalent cations in the conversion of PM to laser-induced blue membrane (LIBM; lambda(max)= 605 nm) upon irradiation with intense 532 nm pulses by contrasting the photoconversion of PM with that of monomeric BR solubilized in reduced Triton X-100 detergent. Monomeric BR forms a previously unreported colorless monomer photoproduct which lacks a chromophore band in the visible region but manifests a new band centered near 360 nm similar to the 360 nm band in LIBM. The 360 nm band in both LIBM and colorless monomer originates from a Schiff base-reduced retinyl chromophore which remains covalently linked to bacterioopsin. Both the PM-->LIBM and monomer-->colorless monomer photoconversions are mediated by similar biphotonic mechanisms, indicating that the photochemistry is localized within single BR monomers and is not influenced by BR-BR interactions. The excessively large two-photon absorptivities (> or =10(6) cm(4) s molecule(-1) photon(-1)) of these photoconversions, the temporal and spectral characteristics of pulses which generate LIBM in high yield, and an action spectrum for the PM-->LIBM photoconversion all indicate that the PM-->LIBM and Mon-->CMon photoconversions are both mediated by a sequential biphotonic mechanism in which is the intermediate which absorbs the second photon. The purple-->blue color change results from subsequent conformational perturbations of the PM lattice which induce the removal of Ca(2+) and Mg(2+) ions from the PM surface.
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Affiliation(s)
- Mark B Masthay
- Department of Chemistry, Murray State University, 456 Blackburn Science Building, Murray, Kentucky 42071-3346, USA.
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Marrero H, Rothschild KJ. Bacteriorhodopsin's M412and BR605protein conformations are similar Significance for proton transport. FEBS Lett 2001. [DOI: 10.1016/0014-5793(87)80306-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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8
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Abstract
A simple model for electrostatic interactions in proteins, based on a distance and position dependent screening of the electrostatic potential, is presented. It is applied in conjunction with a Monte Carlo algorithm to calculate pK(alpha) values of ionizable groups in proteins. The purpose is to furnish a simple, fast, and sufficiently accurate model to be incorporated into molecular dynamic simulations. This will allow for dynamic protonation calculations and for coupling between changes in structure and protonation state during the simulation. The best method of calculating protonation states available today is based on solving the linearized Poisson-Boltzmann equation on a finite difference grid. However, this model consumes far too much computer time to be a practical alternative. Tests are reported for fixed structures on bacteriorhodopsin, lysozyme, myoglobin, and calbindin. The studies include comparisons with Poisson-Boltzmann calculations with dielectric constants 4 and 20 inside the protein, a model with uniform dielectric constant 80 and distance-dependent dielectric models. The accuracy is comparable to that of Poisson-Boltzmann calculations with dielectric constant 20, and it is considerably better than that with epsilon = 4. The time to calculate the protonation at one pH value is at least 100 times less than that of a Poisson-Boltzmann calculation. Proteins 1999;36:474-483.
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Affiliation(s)
- L Sandberg
- Theoretical Physics, Royal Institute of Technology, Stockholm, Sweden
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9
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Dioumaev AK, Brown LS, Needleman R, Lanyi JK. Fourier transform infrared spectra of a late intermediate of the bacteriorhodopsin photocycle suggest transient protonation of Asp-212. Biochemistry 1999; 38:10070-8. [PMID: 10433714 DOI: 10.1021/bi990873+] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We measured time-resolved difference spectra, in the visible and the infrared, for the Glu-194 and Glu-204 mutants of bacteriorhodopsin and detected an anomalous O state, labeled O', in addition to the authentic O intermediate, before recovery of the initial state in the photocycle. The O' intermediate exhibits prominent bands at 1712 cm(-1) (positive) and 1387 cm(-1) (negative). These bands arise with the same time constant as the deprotonation of Asp-85. Both bands are shifted to lower frequency upon labeling of the protein with [4-(13)C]aspartic acid. The former band, but not the latter, is shifted in D2O. These shifts identify the two bands as the carboxyl stretch of a protonated aspartic acid and the symmetric carbonyl stretch of an unprotonated aspartate, respectively, and suggest that in O' an initially anionic aspartate enters into protonation equilibrium with Asp-85. Elimination of the few other candidates, on various grounds, identifies Asp-212 as the unknown residue. It is possible, therefore, that in the last step of the photocycle of the mutants studied the proton released from Asp-85 is conducted to the extracellular surface via Asp-212. An earlier report of a weak band at 1712 cm(-1) late in the wild-type photocycle [Zscherp and Heberle (1997) J. Phys. Chem. B 101, 10542-10547] suggests that Asp-212 might play this role in the wild-type protein also.
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Affiliation(s)
- A K Dioumaev
- Department of Physiology and Biophysics, University of California, Irvine 92697, USA
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10
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Kelemen L, Galajda P, Száraz S, Ormos P. Chloride ion binding to bacteriorhodopsin at low pH: an infrared spectroscopic study. Biophys J 1999; 76:1951-8. [PMID: 10096893 PMCID: PMC1300171 DOI: 10.1016/s0006-3495(99)77354-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Bacteriorhodopsin (bR) and halorhodopsin (hR) are light-induced ion pumps in the cell membrane of Halobacterium salinarium. Under normal conditions bR is an outward proton transporter, whereas hR is an inward Cl- transporter. There is strong evidence that at very low pH and in the presence of Cl-, bR transports Cl- ions into the cell, similarly to hR. The chloride pumping activity of bR is connected to the so-called acid purple state. To account for the observed effects in bR a tentative complex counterion was suggested for the protonated Schiff base of the retinal chromophore. It would consist of three charged residues: Asp-85, Asp-212, and Arg-82. This quadruplet (including the Schiff base) would also serve as a Cl- binding site at low pH. We used Fourier transform infrared difference spectroscopy to study the structural changes during the transitions between the normal, acid blue, and acid purple states. Asp-85 and Asp-212 were shown to participate in the transitions. During the normal-to-acid blue transition, Asp-85 protonates. When the pH is further lowered in the presence of Cl-, Cl- binds and Asp-212 also protonates. The binding of Cl- and the protonation of Asp-212 occur simultaneously, but take place only when Asp-85 is already protonated. It is suggested that HCl is taken up in undissociated form in exchange for a neutral water molecule.
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Affiliation(s)
- L Kelemen
- Institute of Biophysics, Biological Research Center of the Hungarian Academy of Sciences, Szeged, H-6701 Hungary
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11
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Rüdiger M, Tittor J, Gerwert K, Oesterhelt D. Reconstitution of bacteriorhodopsin from the apoprotein and retinal studied by Fourier-transform infrared spectroscopy. Biochemistry 1997; 36:4867-74. [PMID: 9125507 DOI: 10.1021/bi962426p] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The reconstitution of the retinal-containing protein bacteriorhodopsin (BR) from the apoprotein and retinal has been studied by Fourier-transform infrared (FTIR) difference spectroscopy. 9-cis-Retinal which occupies the binding site but does not reconstitute the chromophore was used as "caged retinal". Photoisomerization to the all-trans isomer triggers the reconstitution reaction. Absorption bands in the FTIR difference spectra of the educt and product of the reaction could be assigned by comparison with a 9-cis-retinal FTIR spectrum or an FT-Raman spectrum of BR and due to band shifts observed upon deuterium exchange. Specific difference bands were assigned to the protonated carboxyl groups of D96 and D115 by use of the mutants D115N and D96N. Both aspartic acids are protonated also in the apoprotein with pKa values above 10 and undergo a frequency shift toward higher wavenumbers indicating a more hydrophobic environment in the reconstituted protein. No indication was found for protonation changes of carboxyl groups or other protonatable residues when carrying out the reaction at pH values between 4 and 10. The pH-dependent protonation changes reported earlier [Fischer & Oesterhelt (1980) Biophys. J. 31, 139-146] therefore may be caused by protons in a hydrogen-bonded network. Mutations of E204, but not of D38 or E9, cancel proton uptake during reconstitution at high pH as well as proton release at low pH. It is concluded, that E204, without changing its protonation state itself, is part of a protonatable hydrogen-bonded network which changes its pKa during reconstitution thereby causing the observed protonation changes.
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Affiliation(s)
- M Rüdiger
- Max-Planck-Institut für Biochemie, Martinsried, Germany
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12
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Sandberg L, Edholm O. pKa calculations along a bacteriorhodopsin molecular dynamics trajectory. Biophys Chem 1997; 65:189-204. [PMID: 17029855 DOI: 10.1016/s0301-4622(96)02262-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/1996] [Accepted: 12/04/1996] [Indexed: 10/18/2022]
Abstract
Electrostatic calculations of pK(a-values) are reported along a 400 ps molecular dynamics trajectory of bacteriorhodopsin. The sensitivity of calculated pK(a) values to a number of structural factors and factors related to the modelling of the electrostatics are also studied. The results are very sensitive to the choice of internal dielectric constant of the protein (in the interval 2-4). Moreover it is important to include internal water molecules and to average over a long enough portion ( approximately 100 ps) of an equilibrium molecular dynamics trajectory. The internal waters are necessary to get an ion-counter ion complex with the Schiff base and Arg 82 protonated and the aspartic groups (85 and 212) deprotonated. The fluctuations along the MD-trajectory do not change the protonation state of internal residues at neutral pH. However, at other pH values the averaging along a trajectory maybe crucial to get correct protonation states. A relationship is found between the arginine group 82, the aspartic group 85 and the glutamate group 204. Glu 204 is protonated in the ground state but the pK(a) value decreases towards deprotonation when the chromophore isomerizes into the cis state.
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Affiliation(s)
- L Sandberg
- Theoretical Physics, Royal Institute of Technology, S-100 44 Stockholm 70, Sweden
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13
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Engels M, Gerwert K, Bashford D. Computational studies of the early intermediates of the bacteriorhodopsin photocycle. Biophys Chem 1995; 56:95-104. [PMID: 7662874 DOI: 10.1016/0301-4622(95)00020-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Starting from a refined model of bacteriorhodopsin's ground state, alternative models of the K and L intermediates with retinal in either 13-cis or 13-14-dicis configuration have been generated by molecular dynamics simulations. All models have been submitted to electrostatic calculations in order to determine the pK1/2 values of particular residues of interest in the active site. Our pK1/2 calculations for the refined ground state can reestablish our former results, this time without adjusting the intrinsic pK of the Schiff base. For the K intermediate the electrostatic calculations show no significant change in the pK1/2 values compared to the ground state for most of the titrating groups in the active site. For the L intermediate where retinal possesses a 13-cis configuration, we found that electrostatic factors decrease the pK1/2 value of the Schiff base by 4-5 pK-units compared to the ground state. The calculations suggest that changes of the electrostatic environment via a pure 13-cis model are sufficient to produce a pK reduction of the Schiff base that will promote subsequent proton transfer steps.
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Affiliation(s)
- M Engels
- Scripps Research Institute, Department of Molecular Biology, La Jolla, CA 92037, USA
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14
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le Coutre J, Rüdiger M, Oesterhelt D, Gerwert K. FTIR investigation of the blue to acid-purple transition of Bacteriorhodopsin by use of induced halide binding. J Mol Struct 1995. [DOI: 10.1016/0022-2860(95)08735-e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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15
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Wakatsuki S, Kimura Y, Stoeckenius W, Gillis N, Eliezer D, Hodgson KO, Doniach S. Blue form of bacteriorhodopsin and its order-disorder transition during dehydration. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1185:160-6. [PMID: 8167134 DOI: 10.1016/0005-2728(94)90206-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Freshly-prepared blue membranes from Halobacterium halobium, previously reported to be disordered, are shown to have a distinct crystal lattice structure, slightly different from the native form. The lattice of the blue form is disrupted irreversibly when dehydrated. The disorder process was observed using time-resolved small-angle X-ray diffraction and analyzed by radial autocorrelation functions. The diffraction peaks of the in-plane lattice first sharpen and increase due to improved membrane orientation, then the trimer lattice becomes disordered and the unit cell dimension decreases by 1.8 A. In contrast, dehydration of purple membranes does not disorder the lattice, and the unit cell dimension shrinks by only 1.0 A. Comparisons of radial autocorrelation functions for the blue membrane during drying show drastic loss of inter-trimer, long-range correlation while the intra-trimer, short-range correlations remain more or less unchanged. This suggests that the deionized protein trimers can maintain their overall structure during the dehydration, even though the lattice dimension decreases appreciably and the two-dimensional crystallinity is disrupted.
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Affiliation(s)
- S Wakatsuki
- Department of Chemistry, Stanford University, CA 94305
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16
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Olejnik J, Brzezinski B, Zundel G. A proton pathway with large proton polarizability and the proton pumping mechanism in bacteriorhodopsin — Fourier transform difference spectra of photoproducts of bacteriorhodopsin and of its pentademethyl analogue. J Mol Struct 1992. [DOI: 10.1016/0022-2860(92)80123-y] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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17
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Metz G, Siebert F, Engelhard M. Asp85 is the only internal aspartic acid that gets protonated in the M intermediate and the purple-to-blue transition of bacteriorhodopsin. A solid-state 13C CP-MAS NMR investigation. FEBS Lett 1992; 303:237-41. [PMID: 1318849 DOI: 10.1016/0014-5793(92)80528-o] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
High-resolution solid-state 13C NMR spectra of the ground state and M intermediate of the bacteriorhodopsin mutant D96N with the isotope label at [4-13C]Asp and [11-13C]Trp were recorded. The NMR spectra show that Asp85 is protonated in the M intermediate. The environment of Asp85 is quite hydrophobic. On the other hand, Asp212 remains deprotonated and a slight shift to lower field indicates a more hydrophilic environment. Asp85 also protonates in the purple-to-blue transition of bacteriorhodopsin in the deionized membrane, where it experiences a similar environment to M. The shift of Trp resonances in M reflect a conformational change of the protein in forming the M intermediate.
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Affiliation(s)
- G Metz
- Institut für Biophysik und Strahlenbiologie der Universität, Freiburg, Germany
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18
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Bashford D, Gerwert K. Electrostatic calculations of the pKa values of ionizable groups in bacteriorhodopsin. J Mol Biol 1992; 224:473-86. [PMID: 1313886 DOI: 10.1016/0022-2836(92)91009-e] [Citation(s) in RCA: 468] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The effects of solvation and charge-charge interactions on the pKa of ionizable groups in bacteriorhodopsin have been studied using a macroscopic dielectric model with atom-level detail. The calculations are based on the atomic model for bacteriorhodopsin recently proposed by Henderson et al. Even if the structural data are not resolved at the atomic level, such calculations can indicate the quality of the model, outline some general aspects of electrostatic interactions in membrane proteins, and predict some features. The effects of structural uncertainties on the calculations have been investigated by conformational sampling. The results are in reasonable agreement with experimental measurements of several unusually large pKa shifts (e.g. the experimental findings that Asp96 and Asp115 are protonated in the ground state over a wide pH range). In general, we find that the large unfavorable desolvation energies of forming charges in the protein interior must be compensated by strong favorable charge-charge interactions, with the result that the titrations of many ionizable groups are strongly coupled to each other. We find several instances of complex titration behavior due to strong electrostatic interactions between titrating sites, and suggest that such behavior may be common in proton transfer systems. We also propose that they can help to resolve structural ambiguities in the currently available density map. In particular, we find better agreement between theory and experiment when a structural ambiguity in the position of the Arg82 side-chain is resolved in favor of a position near the Schiff base.
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Affiliation(s)
- D Bashford
- Scripps Research Institute, La Jolla, CA 92037
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19
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Rivière ME, Arrio B, Pansu R, Faure J. Influence of the surface potential on the purple membrane structure and activity. Arch Biochem Biophys 1991; 284:1-8. [PMID: 1989488 DOI: 10.1016/0003-9861(91)90253-f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The role of the divalent cations in the purple membrane is generally understood as the release mechanism of the blue form appearance. The reconstitution by cation addition leads to the recovery of the initial spectral properties. Numerous data are available in the literature on this matter but they are scattered, so that synthetic understanding is not easy. The role of divalent cations was studied through spectrophotometric titrations and electrophoretic mobility measurements, i.e., zeta potential valuations. Thus, correlations between the bacteriorhodopsin (bR) state and the whole membrane in equilibrium with a definite medium could be made. Deionization was not a fully reversible process. The absence of cations affect neither the rate of the M412 formation nor its lifetime but the yield of M412/bR was 50% lower. The number of protons involved in the blue to purple transition of both membranes was different and the reconstitution did not erase this difference. It was observed that the number of protons dissociated upon cation addition corresponded approximately to the number of positive charges removed by deionization. Electrophoretic mobility titrations showed large differences between the membranes, illustrating the influence of the surface charge density on the pK of the transition. Taking advantage of the reversible light adaptation process, the reciprocal influence of the charge density of the membrane surface and the retinal state in bR was shown. Specificity of the divalent cations was questioned by a direct substitution of them by imidazol, which left the membrane intact. The partial reversibility of the deionization, the decrease of the M412 yield, the differences in the titratable protons, and the nonstrict specificity toward divalent cations suggested that another unknown factor could be removed from the membrane.
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Affiliation(s)
- M E Rivière
- C.N.R.S. URA 1116, Bioénergétique Membranaire, Bât. 433, Université de Paris-Sud, Orsay, France
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Renthal R, Shuler K, Regalado R. Control of bacteriorhodopsin color by chloride at low pH. Significance for the proton pump mechanism. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1016:378-84. [PMID: 2158820 DOI: 10.1016/0005-2728(90)90172-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The chromophore of bacteriorhodopsin undergoes a transition from purple (570 nm absorbance maximum) to blue (605 nm absorbance maximum) at low pH or when the membrane is deionized. The blue form was stable down to pH 0 in sulfuric acid, while 1 M NaCl at pH 0 completely converted the pigment to a purple form absorbing maximally at 565 Other acids were not as effective as sulfuric in maintaining the blue form, and chloride was the best anion for converting blue membrane to purple membrane at low pH. The apparent dissociation constant for Cl- was 35 mM at pH 0, 0.7 M at pH 1 and 1.5 M at pH 2. The pH dependence of apparent Cl- binding could be modeled by assuming two different types of chromophore-linked Cl- binding site, one pH-dependent. Chemical modification of bacteriorhodopsin carboxyl groups (probably Asp-96, -102 and/or -104) by 1-ethyl-3-dimethlyaminopropyl carbodiimide, Lys-41 by dansyl chloride, or surface arginines by cyclohexanedione had no effect on the conversion of blue to purple membrane at pH 1. Fourier transform infrared difference spectroscopy of chloride purple membrane minus acid blue membrane showed the protonation of a carboxyl group (trough at 1392 cm -1 and peak at 1731 cm -1). The latter peak shifted to 1723 cm -1 in D2O. Ultraviolet difference spectroscopy of chloride purple membrane minus acid blue membrane showed ionization of a phenolic group (peak at 243 nm and evidence for a 295 nm peak superimposed on a tryptophan perturbation trough). This suggests the possibility of chloride-induced proton transfer from a tyrosine phenolic group to a carboxylate side-chain. We propose a mechanism for the purple to acid blue to chloride purple transition based on these results and the proton pump model of Braiman et al. (Biochemistry 27 (1988) 8516-8520).
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Affiliation(s)
- R Renthal
- Division of Earth and Physical Science, University of Texas, San Antonio 78285
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22
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Duñach M, Padrós E, Muga A, Arrondo JL. Fourier-transform infrared studies on cation binding to native and modified purple membranes. Biochemistry 1989; 28:8940-5. [PMID: 2605235 DOI: 10.1021/bi00448a038] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Fourier-transform infrared spectroscopy has been used to examine the structural differences in the protein moiety between the native purple and the deionized blue membranes, both at pH 5.0. The spectra demonstrate that deionization of purple membrane decreases the content of the distorted alpha II-helices in favor of the more common alpha I-helices. Changes in the signals from beta-turns are also observed. The changes corresponding to the carboxyl groups suggest that deionization leads to a decrease in the strength of the hydrogen bonds involving carboxyl groups. Most of these effects are reversed progressively upon binding of one to five Mn2+ per bacteriorhodopsin to the deionized membrane. Binding of Hg2+ to the deionized membranes does not restore the purple color but induces global changes similar to, but less intense than, those brought about by Mn2+ binding. However, the effects attributed to the carboxyl groups are opposite to those found for Mn2+. Schiff base reduction or bleaching induces a decrease of the content of the alpha II-helix in favor of the alpha I-helix and a decrease in the strength of hydrogen bonds to carboxyl groups. Deionization of these modified membranes leads to a further loss in the alpha II content. These results indicate a conformational rearrangement of the protein structure between the native purple membrane and the deionized membrane, which could arise from surface potential changes elicited by bound cations. The changes observed in the carboxyl groups suggest that some of them are located structurally close to the retinal environment and may be involved in cation binding.
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Affiliation(s)
- M Duñach
- Departament de Bioquímica i Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Spain
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23
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Hrabeta-Robinson E, Semadeni M, Packer L. Role of carboxyl residues and membrane lipids in cation binding to bacteriorhodopsin. Arch Biochem Biophys 1989; 269:476-84. [PMID: 2493216 DOI: 10.1016/0003-9861(89)90131-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
To investigate the site specificity of cation binding to bacteriorhodopsin, carboxyl groups were chemically modified in purple membrane preparations from Halobacterium halobium. Cation binding followed by EPR and visible spectroscopy has led us to the conclusion that two cations bind to the surface regions and that at least one cation binds to carboxyl groups in the protein interior. Conformational freedom is necessary for the cooperative conversion of deionized blue species to cation-reconstituted purple species. Studies of white membranes from the JW-5 strain showed that a higher content of charged lipids results in the binding of approximately 100 more color-regulating cations and in negative cooperativity in the blue-to-purple species conversion. A greater dependence of protein structure on these bound cations suggests a role for cations in the modulation of opsin-lipid interaction.
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Affiliation(s)
- E Hrabeta-Robinson
- Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720
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24
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Tsuji K, Hess B. Proton—magnesium exchange during the blue—purple transition of bacteriorhodopsin. J Electroanal Chem (Lausanne) 1988. [DOI: 10.1016/0022-0728(80)80346-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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25
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Ihara K, Mukohata Y. Proteoliposomes with right-side-out oriented purple membrane/bacteriorhodopsin require cations inside for proton pumping. FEBS Lett 1988; 240:148-52. [PMID: 2847944 DOI: 10.1016/0014-5793(88)80357-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Proteoliposomes were prepared by sonication of phospholipids and blue membranes (cation-free purple membranes carrying little activity of light-driven proton pumping) in an acidic medium of very low ionic strength. The majority of the bacteriorhodopsin population in these proteoliposomes was in the right-side-out (as in living cells) orientation as judged from the resultant polypeptides after papain digestion. By raising the pH of sonication, the population of right-side-out oriented bacteriorhodopsin decreased, and consequently that of the inversely oriented one increased. In KCl and NaCl up to certain concentrations or in choline chloride even at high concentrations, in the light, the proteoliposomes with right-side-out bacteriorhodopsin did not pump protons, whereas those with inversely oriented bacteriorhodopsin did. The former began to pump only after cations were likely incorporated/permeated into the proteoliposome and reached the carboxyl terminal (cytosol) side of bacteriorhodopsin/purple membrane.
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Affiliation(s)
- K Ihara
- Department of Biology, Faculty of Science, Osaka University, Toyonaka, Japan
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26
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Influence of cations on the blue to purple transition of bacteriorhodopsin. Comparison of Ca2+ and Hg2+ binding and their effect on the surface potential. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77846-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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27
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Cladera J, Galisteo ML, Dun˜ach M, Mateo PL, Padrós E. Thermal denaturation of deionized and native purple membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1988. [DOI: 10.1016/0005-2736(88)90546-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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28
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29
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On the molecular mechanism of the blue to purple transition of bacteriorhodopsin. UV-difference spectroscopy and electron spin resonance studies. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68535-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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30
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Electrooptical analysis of blue and of cation-regenerated bacteriorhodopsin. EUROPEAN BIOPHYSICS JOURNAL: EBJ 1987. [DOI: 10.1007/bf00577071] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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