1
|
Buhrke D, Hildebrandt P. Probing Structure and Reaction Dynamics of Proteins Using Time-Resolved Resonance Raman Spectroscopy. Chem Rev 2019; 120:3577-3630. [PMID: 31814387 DOI: 10.1021/acs.chemrev.9b00429] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The mechanistic understanding of protein functions requires insight into the structural and reaction dynamics. To elucidate these processes, a variety of experimental approaches are employed. Among them, time-resolved (TR) resonance Raman (RR) is a particularly versatile tool to probe processes of proteins harboring cofactors with electronic transitions in the visible range, such as retinal or heme proteins. TR RR spectroscopy offers the advantage of simultaneously providing molecular structure and kinetic information. The various TR RR spectroscopic methods can cover a wide dynamic range down to the femtosecond time regime and have been employed in monitoring photoinduced reaction cascades, ligand binding and dissociation, electron transfer, enzymatic reactions, and protein un- and refolding. In this account, we review the achievements of TR RR spectroscopy of nearly 50 years of research in this field, which also illustrates how the role of TR RR spectroscopy in molecular life science has changed from the beginning until now. We outline the various methodological approaches and developments and point out current limitations and potential perspectives.
Collapse
Affiliation(s)
- David Buhrke
- Technische Universität Berlin, Institut für Chemie, Sekr. PC14, Straße des 17, Juni 135, D-10623 Berlin, Germany
| | - Peter Hildebrandt
- Technische Universität Berlin, Institut für Chemie, Sekr. PC14, Straße des 17, Juni 135, D-10623 Berlin, Germany
| |
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
El-Sayed MA, Yang D, Yoo SK, Zhang N. The Effect of Different Metal Cation Binding on the Proton Pumping in Bacteriorhodopsin. Isr J Chem 2013. [DOI: 10.1002/ijch.199500043] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
4
|
Corcoran TC, Ismail KZ, El-Sayed MA. Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin. Proc Natl Acad Sci U S A 2010; 84:4094-8. [PMID: 16593849 PMCID: PMC305029 DOI: 10.1073/pnas.84.12.4094] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The removal of metal cations inhibits the deprotonation process of the protonated Schiff base during the photocycle of bacteriorhodopsin. To understand the nature of the involvement of these cations, a spectroscopic and kinetic study was carried out on bacteriorhodopsin samples in which the native Ca(2+) and Mg(2+) were replaced by Eu(3+), a luminescent cation. The decay of Eu(3+) emission in bacteriorhodopsin can be fitted to a minimum of three decay components, which are assigned to Eu(3+) emission from three different sites. This is supported by the response of the decay components to the presence of (2)H(2)O and to the changes in the Eu(3+)/bR molar ratio. The number of water molecules coordinated to Eu(3+) in each site is determined from the change in its emission lifetime when (2)H(2)O replaces H(2)O. Most of the emission originates from two "wet" sites of low crystal-field symmetry-e.g., surface sites. Protonated Schiff base deprotonation has no discernable effect on the emission decay of protein-bound Eu(3+), suggesting an indirect involvement of metal cations in the deprotonation process. Adding Eu(3+) to deionized bacteriorhodopsin increases the emission intensity of each Eu(3+) site linearly, but the extent of the deprotonation (and color) changes sigmoidally. This suggests that if only the emitting Eu(3+) ions cause the deprotonation and bacteriorhodopsin color change, ions in more than one site must be involved-e.g., by inducing protein conformation changes. The latter could allow deprotonation by the interaction between the protonated Schiff base and a positive field of cations either on the surface or within the protein.
Collapse
Affiliation(s)
- T C Corcoran
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90024
| | | | | |
Collapse
|
5
|
Wang J. Photocurrent from Oriented Membrane Films Containing Acid-blue and Acid-purple Bacteriorhodopsin and its Mutants. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2000)0710476pfomfc2.0.co2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
6
|
Wang J, El-Sayed MA. The Effect of Metal Cation Binding on the Protein, Lipid and Retinal Isomeric Ratio in Regenerated Bacteriorhodopsin of Purple Membrane¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2001)0730564teomcb2.0.co2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
7
|
Kietis BP, Saudargas P, Vàró G, Valkunas L. External electric control of the proton pumping in bacteriorhodopsin. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2006; 36:199-211. [PMID: 17186234 DOI: 10.1007/s00249-006-0120-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 10/18/2006] [Accepted: 11/28/2006] [Indexed: 10/23/2022]
Abstract
Comparative analysis of the photoelectric response of dried films of purple membranes (PM) depending on their degree of orientation is presented. Time dependence of the photo-induced protein electric response signal (PERS) of oriented and non-oriented films to a single laser pulse in the presence of the external electric field (EEF) was experimentally determined. The signal does not appear in the non-oriented films when the EEF is absent, whereas the PERS of the oriented PM films demonstrates the variable polarity on the microsecond time scale. In the presence of the EEF the PERS of the non-oriented film rises exponentially preserving the same polarization. The polarization of the PERS changes by changing the polarity of the EEF with no influence on the time constant of the PERS kinetics. The EEF effect on the PERS of the oriented films is more complicated. By subtracting the PERS when EEF not equal 0 from the PERS when EEF = 0 the resulting signal is comparable to that of the non-oriented films. Generalizing the experimental data we conclude that the EEF influence is of the same origin for the films of any orientation. To explain the experimental results the two-state model is suggested. It assumes that the EEF directionally changes the pK(a) values of the Schiff base (SB) and of the proton acceptor aspartic acid D85 in bacteriorhodopsin. Because of that the SB-->D85 proton transfer might be blocked and consequently the L-->M intermediate transition should vanish. Thus, on the characteristic time scale tau( L --> M ) approximately 30 micros; both intermediates, the M intermediate, appearing under normal conditions, and the L intermediate as persisting under the blocked conditions when D85 is protonated, should coexist in the film. The total PERS is a result of the potentials corresponding to the electrogenic products of intermediates L and M that are of the opposite polarity. It is concluded that the ratio of bacteriorhodopsin concentrations corresponding to the L and M intermediates is driven by the EEF and, consequently, it should define the PERS of the non-oriented films. According to this model the orientation degree of the film could be evaluated by describing the PERS.
Collapse
|
8
|
Sanii LS, Schill AW, Moran CE, El-Sayed MA. The protonation-deprotonation kinetics of the protonated Schiff base in bicelle bacteriorhodopsin crystals. Biophys J 2005; 89:444-51. [PMID: 15821169 PMCID: PMC1366545 DOI: 10.1529/biophysj.105.059675] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the recently published x-ray crystal structure of the "bicelle" bacteriorhodopsin (bbR) crystal, the protein has quite a different structure from the native and the in cubo bacteriorhodopsin (cbR) crystal. Instead of packing in parallel trimers as do the native membrane and the cbR crystals, in the bbR crystal the protein packs as antiparallel monomers. To date, no functional studies have been performed, to our knowledge, to investigate if the photocycle is observed in this novel protein packing structure. In this study, both Raman and time-resolved transient absorption spectroscopy are used to both confirm the presence of the photocycle and investigate the deprotonation-reprotonation kinetics of the Schiff base proton in the bbR crystal. The observed rates of deprotonation and reprotonation processes of its Schiff base have been compared to those observed for native bR under the same conditions. Unlike the previously observed similarity of the rates of these processes for cbR crystals and those for native bacteriorhodopsin (bR), in bbR crystals the rate of deprotonation has increased by 300%, and the rate of reprotonation has decreased by nearly 700%. These results are discussed in light of the changes observed when native bR is delipidated or monomerized by detergents. Both the change of the hydrophobicity of the environment around the protonated Schiff base and Asp85 and Asp96 (which could change the pKa values of proton donor-acceptor pairs) and the water structure in the bbR crystal are offered as possible explanations for the different observations.
Collapse
Affiliation(s)
- Laurie S Sanii
- Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia
| | | | | | | |
Collapse
|
9
|
Heyes CD, Wang J, Sanii LS, El-Sayed MA. Fourier transform infrared study of the effect of different cations on bacteriorhodopsin protein thermal stability. Biophys J 2002; 82:1598-606. [PMID: 11867472 PMCID: PMC1301958 DOI: 10.1016/s0006-3495(02)75511-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The effect of divalent ion binding to deionized bacteriorhodopsin (dI-bR) on the thermal transitions of the protein secondary structure have been studied by using temperature-dependent Fourier transform infrared (FT-IR) spectroscopy. The native metal ions in bR, Ca(2+), and Mg(2+), which we studied previously, are compared with Mn(2+), Hg(2+), and a large, synthesized divalent organic cation, ((Et)(3)N)(2)Bu(2+). It was found that in all cases of ion regeneration, there is a pre-melting, reversible conformational transition in which the amide frequency shifts from 1665 to 1652 cm(-1). This always occurs at approximately 80 degrees C, independent of which cation is used for the regeneration. The irreversible thermal transition (melting), monitored by the appearance of the band at 1623 cm(-1), is found to occur at a lower temperature than that for the native bR but higher than that for acid blue bR in all cases. However, the temperature for this transition is dependent on the identity of the cation. Furthermore, it is shown that the mechanism of melting of the organic cation regenerated bR is different than for the metal cations, suggesting a difference in the type of binding to the protein (either to different sites or different binding to the same site). These results are used to propose specific direct binding mechanisms of the ions to the protein of deionized bR.
Collapse
Affiliation(s)
- Colin D Heyes
- Laser Dynamics Lab, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | | | | | | |
Collapse
|
10
|
Jang DJ, van den Berg R, El-Sayed M. Absence of tryptophan fluorescence quenching by metal cations in delipidated bacteriorhodopsin. FEBS Lett 2001. [DOI: 10.1016/0014-5793(90)80571-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
11
|
Wang J, El-Sayed MA. Time-resolved Fourier transform infrared spectroscopy of the polarizable proton continua and the proton pump mechanism of bacteriorhodopsin. Biophys J 2001; 80:961-71. [PMID: 11159463 PMCID: PMC1301294 DOI: 10.1016/s0006-3495(01)76075-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Nanosecond-to-microsecond time-resolved Fourier transform infrared (FTIR) spectroscopy in the 3000-1000-cm(-1) region has been used to examine the polarizable proton continua observed in bacteriorhodopsin (bR) during its photocycle. The difference in the transient FTIR spectra in the time domain between 20 ns and 1 ms shows a broad absorption continuum band in the 2100-1800-cm(-1) region, a bleach continuum band in the 2500-2150-cm(-1) region, and a bleach continuum band above 2700 cm(-1). According to Zundel (G., J. Mol. Struct. 322:33-42), these continua appear in systems capable of forming polarizable hydrogen bonds. The formation of a bleach continuum suggests the presence of a polarizable proton in the ground state that changes during the photocycle. The appearance of a transient absorption continuum suggests a change in the polarizable proton or the appearance of new ones. It is found that each continuum has a rise time of less than 80 ns and a decay time component of approximately 300 micros. In addition, it is found that the absorption continuum in the 2100-1800-cm(-1) region has a slow rise component of 190 ns and a fast decay component of approximately 60 micros. Using these results and those of the recent x-ray structural studies of bR(570) and M(412) (H. Luecke, B. Schobert, H.T. Richter, J.-P. Cartailler, and J. K., Science 286:255-260), together with the already known spectroscopic properties of the different intermediates in the photocycle, the possible origins of the polarizable protons giving rise to these continua during the bR photocycle are proposed. Models of the proton pump are discussed in terms of the changes in these polarizable protons and the hydrogen-bonded chains and in terms of previously known results such as the simultaneous deprotonation of the protonated Schiff base (PSB) and Tyr185 and the disappearance of water molecules in the proton release channel during the proton pump process.
Collapse
Affiliation(s)
- J Wang
- Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | | |
Collapse
|
12
|
Wang J, el-Sayed MA. The Effect of Metal Cation Binding on the Protein, Lipid and Retinal Isomeric Ratio in Regenerated Bacteriorhodopsin of Purple Membrane¶. Photochem Photobiol 2001; 73:564-71. [PMID: 11367581 DOI: 10.1562/0031-8655(2001)073<0564:teomcb>2.0.co;2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effect of metal cation binding on bacteriorhodopsin (bR) in purple membrane has been examined using in situ attenuated total reflection-Fourier transform infrared difference spectroscopy in aqueous media. It is known that adding metal cations to deionized bR regenerates the purple state from its blue state and recovers the proton pump function. During this process, infrared spectral changes in the frequency region of 1800-1000 cm-1 are monitored. The results reveal that metal cation binding affects the protein conformation, the retinal isomeric composition as well as lipid head groups. It is also observed that metal cation binding induces conformational changes in the alpha 1-helix region of bR, converting the portion of its alpha 1-helical domain into beta-turn or disordered coil. In addition, the influence of Ho3+ binding on the protein and lipid is observed to be larger than that of Ca2+. These results suggest that some of the metal cation binding sites are on the membrane lipid domain, while others could be on the intrahelical domain or interhelical loops where the Asp and Glu are located (binding with their COO- groups). Our results also suggest that the removal of the C-terminal of bR increase the accessibility of the binding site of metal cations, which affects protein conformational structure. All these observations are discussed in terms of the two proposals given in the literature regarding the metal cation binding sites.
Collapse
Affiliation(s)
- J Wang
- Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | | |
Collapse
|
13
|
Wang J. Photocurrent from oriented membrane films containing acid-blue and acid-purple bacteriorhodopsin and its mutants. Photochem Photobiol 2000; 71:476-80. [PMID: 10824601 DOI: 10.1562/0031-8655(2000)071<0476:pfomfc>2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
This paper investigates the fast photocurrent components, B1 and B2, from oriented bacteriorhodopsin (BR) membrane films at low pH, under pulsed laser excitation. Adding chloride ion changes the acid-blue BR to its acid-purple form. In the presence of chloride, the acid-purple BR shows a positive B2 component in the same direction as that of BR at neutral pH, indicating a rapid intramolecular charge transfer. In the absence of chloride, the acid-blue BR shows only a negative B1 with multi-components, indicating a rapid charge separation process associated with retinal photoisomerization. The multi-components in B1 are possibly formed due to the heterogeneity of the acid-blue BR. In addition, BR mutants, D85N and D115N, at low pH and in the presence of chloride, generate the B2 component as well. The observation of chloride-dependent B2 component in various cases at low pH, is in favor of a possible transient chloride ion transfer, although the nature of the charge being transferred cannot be identified so far.
Collapse
Affiliation(s)
- J Wang
- Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta 30332-0400, USA.
| |
Collapse
|
14
|
Abstract
Adding Ca2+ or other cations to deionized bacteriorhodopsin causes a blue to purple color shift, a result of deprotonation of Asp85. It has been proposed by different groups that the protonation state of Asp85 responds to the binding of Ca2+ either 1) directly at a specific site in the protein or 2) indirectly through the rise of the surface pH. We tested the idea of specific binding of Ca2+ and found that the surface pH, as determined from the ionization state of eosin covalently linked to engineered cysteine residues, rises about equally at both extracellular and cytoplasmic surfaces when only one Ca2+ is added. This precludes binding to a specific site and suggests that rather than decreasing the pKa of Asp85 by direct interaction, Ca2+ increases the surface pH by binding to anionic lipid groups. As Ca2+ is added the surface pH rises, but deprotonation of Asp85 occurs only when the surface pH approaches its pKa. The nonlinear relationship between Ca2+ binding and deprotonation of Asp85 from this effect is different in the wild-type protein and in various mutants and explains the observed complex and varied spectral titration curves.
Collapse
Affiliation(s)
- G Váró
- Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA
| | | | | | | |
Collapse
|
15
|
Zhang K, Song L, Dong J, El-Sayed MA. Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- ions. Biophys J 1997; 73:2097-105. [PMID: 9336205 PMCID: PMC1181110 DOI: 10.1016/s0006-3495(97)78240-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The binding of Zn2+ in Zn2+-regenerated bacteriorhodopsin (bR) was studied under various conditions by x-ray absorption fine structures (XAFS). The 0.9:1 and 2:1 Zn2+:bR samples gave similar XAFS spectra, suggesting that Zn2+ might have only one strong binding site in bR. It was found that in aqueous bR solution, Zn2+ has an average of six oxygen or nitrogen ligands. Upon drying, two ligands are lost, suggesting the existence of two weakly bound water ligands near the cation-binding site in bacteriorhodopsin. When excess Cl- ions were present before drying in the Zn2+-regenerated bR samples, it was found that two of the ligands were replaced by Cl- ions in the dried film, whereas two remain unchanged. The above observations suggest that Zn2+ has three types of ligands in regenerated bR (referred to as types I, II, and III). Type I ligands are strongly bound. These ligands cannot be removed by drying or by exchanging with Cl- ions. Type II ligands cannot be removed by drying, but can be replaced by Cl- ligands. Type III ligands are weakly bound to the metal cation and are most likely water molecules that can be removed by evaporation under vacuum or by drying with anhydrous CaSO4. The results are discussed in terms of the possible structure of the strongly binding site of Zn2+ in bR.
Collapse
Affiliation(s)
- K Zhang
- Biostructures Institute, Philadelphia, Pennsylvania 19104-3358, USA
| | | | | | | |
Collapse
|
16
|
Cao Y, Brown LS, Sasaki J, Maeda A, Needleman R, Lanyi JK. Relationship of proton release at the extracellular surface to deprotonation of the schiff base in the bacteriorhodopsin photocycle. Biophys J 1995; 68:1518-30. [PMID: 7787037 PMCID: PMC1282046 DOI: 10.1016/s0006-3495(95)80324-3] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The surface potential of purple membranes and the release of protons during the bacteriorhodopsin photocycle have been studied with the covalently linked pH indicator dye, fluorescein. The titration of acidic lipids appears to cause the surface potential to be pH-dependent and causes other deviations from ideal behavior. If these anomalies are neglected, the appearance of protons can be followed by measuring the absorption change of fluorescein bound to various residues at the extracellular surface. Contrary to widely held assumption, the activation enthalpies of kinetic components, deuterium isotope effects in the time constants, and the consequences of the D85E, F208R, and D212N mutations demonstrate a lack of direct correlation between proton transfer from the buried retinal Schiff base to D85 and proton release at the surface. Depending on conditions and residue replacements, the proton release can occur at any time between the protonation of D85 and the recovery of the initial state. We conclude that once D85 is protonated the proton release at the extracellular protein surface is essentially independent of the chromophore reactions that follow. This finding is consistent with the recently suggested version of the alternating access mechanism of bacteriorhodopsin, in which the change of the accessibility of the Schiff base is to and away from D85 rather than to and away from the extracellular membrane surface.
Collapse
Affiliation(s)
- Y Cao
- Department of Physiology and Biophysics, University of California, Irvine 92717, USA
| | | | | | | | | | | |
Collapse
|
17
|
Taneva SG, Koynova R, Tenchov B. Thermal stability of lipid-depleted purple membranes at neutral and low pH values. FEBS Lett 1994; 345:154-8. [PMID: 8200449 DOI: 10.1016/0014-5793(94)00426-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Differential scanning calorimetry was used to compare the thermal behavior of native and delipidated purple membrane fragments at pH values corresponding to purple, blue and acid-purple forms. At neutral pH, delipidation results in a 2.5- to 3-times increase in the cooperativity of the denaturational transition, accompanied by a minor increase in its temperature. At pH values below 5 the delipidated membranes exhibit considerably higher thermal stability than the native membranes. The reversible predenaturational transition observed in the native state is not detectable upon delipidation. There is no strict correlation between color changes upon acidification and deionization of either native or delipidated purple membranes and their thermal stability.
Collapse
Affiliation(s)
- S G Taneva
- Central Laboratory of Biophysics, Bulgarian Academy of Sciences, Sofia
| | | | | |
Collapse
|
18
|
Taneva S, Jordanova N, Petkanchin I. Electro-optical investigation of lipid-depleted purple membranes. Biophys Chem 1992. [DOI: 10.1016/0301-4622(92)85041-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
19
|
Taneva SG, Petkanchin IB, Todorov G, Stoylov SP. Influence of cation binding on the electro-optically determined electric moments of purple membranes. Adv Colloid Interface Sci 1992; 38:299-317. [PMID: 1575932 DOI: 10.1016/0001-8686(92)80048-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Analysis of the electro-optically determined permanent dipole moment and electric polarizability of purple membrane fragments reveals the complex nature of the membrane electric moments. The problem to distinguish between the contribution of the membrane structural charges (charged groups of the polypeptide chain and polar lipid headgroups), bound cations and the electric double layer structure deserves particular attention not only because of its importance for electro-optics but also in respect to the relation of the membrane surface electric properties to the membrane transport function. The removal of divalent cations (Ca2+ and Mg2+) bound to purple membrane in the native state induces a cation-free species of purple membrane (deionized--blue membrane) with drastically changed spectroscopic properties and function. The present paper summarizes our study on the electric moments of blue membrane and their changes during the blue to purple transition. We intended to provide an insight into the possible regulation of this reversible transition (purple-to-blue and blue-to-purple) through changes of the asymmetric charge distribution and the importance of the asymmetric interfacial charge distribution for the proton transfer in purple membranes. The changes in the electric moments (permanent and induced dipole moments) of purple membrane fragments upon di- and trivalent cations binding to cation-depleted purple membranes were studied by electric light scattering (rotational electrokinetics) in d.c. and a.c. electric fields, and by electric pulses with reversing polarity. The results show a recovery of the membrane charge asymmetry (permanent dipole moment) though not of the induced dipole moment.
Collapse
Affiliation(s)
- S G Taneva
- Central Laboratory of Biophysics, Bulgarian Academy of Sciences, Sofia
| | | | | | | |
Collapse
|
20
|
Maeda A, Sasaki J, Pfefferlé JM, Shichida Y, Yoshizawa T. FOURIER TRANSFORM INFRARED SPECTRAL STUDIES ON THE SCHIFF BASE MODE OF ALL-trans BACTERIORHODOPSIN and ITS PHOTOINTERMEDIATES, K and L. Photochem Photobiol 1991. [DOI: 10.1111/j.1751-1097.1991.tb02111.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
21
|
Sweetman LL, el-Sayed MA. The binding site of the strongly bound Eu3+ in Eu(3+)-regenerated bacteriorhodopsin. FEBS Lett 1991; 282:436-40. [PMID: 2037059 DOI: 10.1016/0014-5793(91)80531-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A Scatchard plot for the strongly bound Eu3+ to deionized bacteriorhodopsin (bR) was made using a method based on measuring the concentration of unbound Eu3+ from its fluorescence intensity. The results suggest that the first mole of Eu3+ added to a mole of bR is strongly bound by displacing 2-3 protons. In order to reconcile this result with the previous time-resolved fluorescence studies on Eu(3+)-regenerated bR, which showed the presence of 3 sites of comparable binding constants, one is forced to conclude that the emission from the strongly bound Eu3+ is completely quenched, e.g. by energy transfer to the retinal. For this to take place, the Eu3+ must be within a few A from the retinal, i.e. within the retinal pocket (the active site). The possible importance of this conclusion to the deprotonation mechanism of the protonated Schiff base, the switch of the proton pump in bR, is discussed.
Collapse
Affiliation(s)
- L L Sweetman
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024
| | | |
Collapse
|
22
|
The thermal stability of native, delipidated, deionized and regenerated bacteriorhodopsin. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1990. [DOI: 10.1016/1011-1344(90)85163-q] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
23
|
Nasuda-Kouyama A, Fukuda K, Iio T, Kouyama T. Effect of a light-induced pH gradient on purple-to-blue and purple-to-red transitions of bacteriorhodopsin. Biochemistry 1990; 29:6778-88. [PMID: 2168741 DOI: 10.1021/bi00481a005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Bacteriorhodopsin-containing vesicles that were able to alkalize the extravesicular medium by greater than 1.5 pH units under illumination, i.e., inside-out vesicles, were reconstituted by reverse-phase evaporation with Halobacterium halobium polar lipids or exogenous phospholipids. Acid titration of a dark-adapted sample was accompanied by a color change from purple to blue (pKa = 2.5-4.5 in 0.15 M K2SO4), and alkali titration resulted in the formation of a red species absorbing maximally at 480 nm (pKa = 7 to greater than 9), the pKa values and the extents of these color changes being dependent on the nature of lipid. When a vesicle suspension at neutral or weakly acidic pH was irradiated by continuous light so that a large pH gradient was generated across the membrane, either a purple-to-blue or a purple-to-red transition took place. The light-induced purple-to-red transition was significant in an unbuffered vesicle suspension and correlated with the pH change in the extravesicular medium. The result suggests that the purple-to-red transition is driven from the extravesicular side, i.e., from the C-terminal membrane surface. In the presence of buffer molecules outside, the dominant color change induced in the light was the purple-to-blue transition, which seemed to be due to a large decrease in the intravesicular pH. But an apparently inconsistent result was obtained when the extravesicular medium was acidified by a HCl pulse, which was accompanied by a rapid color change to blue. We arrived at the following explanation: The two bR isomers, one containing all-trans-retinal and the other 13-cis-retinal, respond differently to pH changes in the extravesicular and the intravesicular medium. In this relation, full light adaptation was not achieved when the light-induced purple-to-blue transition was significant; i.e., only the 13-cis isomer is likely to respond to a pH change at the N-terminal membrane surface.
Collapse
|
24
|
de Groot HJ, Smith SO, Courtin J, van den Berg E, Winkel C, Lugtenburg J, Griffin RG, Herzfeld J. Solid-state 13C and 15N NMR study of the low pH forms of bacteriorhodopsin. Biochemistry 1990; 29:6873-83. [PMID: 2168744 DOI: 10.1021/bi00481a017] [Citation(s) in RCA: 109] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting from 568 nm (pH 7) to approximately 600 nm (pH 2) and back to 565 nm (pH 0) as the pH is decreased further with HCl. Blue membrane (lambda max greater than 600 nm) is also formed by deionization of neutral purple membrane suspensions. Low-temperature, magic angle spinning 13C and 15N NMR was used to investigate the transitions to the blue and acid purple states. The 15N NMR studies involved [epsilon-15N]lysine bR, allowing a detailed investigation of effects at the Schiff base nitrogen. The 15N resonance shifts approximately 16 ppm upfield in the neutral purple to blue transition and returns to its original value in the blue to acid purple transition. Thus, the 15N shift correlates directly with the color changes, suggesting an important contribution of the Schiff base counterion to the "opsin shift". The results indicate weaker hydrogen bonding in the blue form than in the two purple forms and permit a determination of the contribution of the weak hydrogen bonding to the opsin shift at a neutral pH of approximately 2000 cm-1. An explanation of the mechanism of the purple to blue to purple transition is given in terms of the complex counterion model. The 13C NMR experiments were performed on samples specifically 13C labeled at the C-5, C-12, C-13, C-14, or C-15 positions in the retinylidene chromophore. The effects of the purple to blue to purple transitions on the isotropic chemical shifts for the various 13C resonances are relatively small. It appears that bR600 consists of at least four different species. The data confirm the presence of 13-cis- and all-trans-retinal in the blue form, as in neutral purple dark-adapted bR. All spectra of the blue and acid purple bR show substantial inhomogeneous broadening which indicates additional irregular distortions of the protein lattice. The amount of distortion correlates with the variation of the pH, and not with the color change.
Collapse
Affiliation(s)
- H J de Groot
- Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139
| | | | | | | | | | | | | | | |
Collapse
|
25
|
Jang DJ, el-Sayed MA, Stern LJ, Mogi T, Khorana HG. Effect of genetic modification of tyrosine-185 on the proton pump and the blue-to-purple transition in bacteriorhodopsin. Proc Natl Acad Sci U S A 1990; 87:4103-7. [PMID: 2349220 PMCID: PMC54055 DOI: 10.1073/pnas.87.11.4103] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The retinylidene chromophore mutant (Y185F) of bacteriorhodopsin, in which Tyr-185 is substituted by phenylalanine, is examined and compared with wild-type bacteriorhodopsin expressed in Escherichia coli; both were reinstituted similarly in vesicles. The Y185F mutant shows (at least) two distinct spectra at neutral pH. Upon light absorption, the blue species (which absorbs in the red) behaves as if "dead"--i.e., neither its tyrosine nor its protonated Schiff base undergoes deprotonation nor does its tryptophan fluorescence undergo quenching. This result is unlike either the purple species (which absorbs in the blue) or wild-type bacteriorhodopsin expressed in E. coli. As the pH increases, both the color changes and the protonated Schiff base deprotonation efficiency suggest a blue-to-purple transition of the Y185F mutant near pH 9. If this blue-to-purple transition of Y185F corresponds to the blue-to-purple transition of purple-membrane (native) bacteriorhodopsin (occurring at pH 2.6) and of wild-type bacteriorhodopsin expressed in E. coli (occurring at pH 5), the protein-conformation changes of this transition as well as the protonated Schiff base deprotonation may be controlled not by surface pH alone, but rather by the coupling between surface potential and the general protein internal structure around the active site. The results also suggest that Tyr-185 does not deprotonate during the photocycle in purple-membrane bacteriorhodopsin.
Collapse
Affiliation(s)
- D J Jang
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024
| | | | | | | | | |
Collapse
|
26
|
Fahmy K, Siebert F. THE PHOTOREACTION OF THE DEIONIZED FORM OF THE PURPLE MEMBRANE INVESTIGATED BY FTIR DIFFERENCE SPECTROSCOPY. Photochem Photobiol 1990. [DOI: 10.1111/j.1751-1097.1990.tb01737.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
27
|
Abstract
It has been known that bacteriorhodopsin, the retinal protein in purple membrane which functions as a light-driven proton pump, undergoes reversible spectroscopic changes at acid pH. The absorption spectra of various bacteriorhodopsin species were estimated from measured spectra of the mixtures that form at low pH, in the presence of sulfate and chloride. The dependency of these on pH and the concentration of Cl- fit a model in which progressive protonation of purple membrane produces "blue membrane", which will bind, with increasing affinity as the pH is lowered, chloride ions to produce "acid purple membrane." Transient spectroscopy with a multichannel analyzer identified the intermediates of the photocycles of these altered pigments, and described their kinetics. Blue membrane produced red-shifted KL-like and L-like products, but no other photointermediates, consistent with earlier suggestions. Unlike others, however, we found that acid purple membrane exhibited a very different photocycle: its first detected intermediate was not like KL in that it was much more red-shifted, and the only other intermediate detectable resembled the O species of the bacteriorhodopsin photocycle. An M-like intermediate, with a deprotonated Schiff base, was not found in either of these photocycles. There are remarkable similarities between the photoreactions of the acid forms of bacteriorhodopsin and the chloride transport system halorhodopsin, where the Schiff base deprotonation seems to be prevented by lack of suitable aspartate residues, rather than by low pH.
Collapse
Affiliation(s)
- G Váró
- Department of Physiology and Biophysics, University of California, Irvine 92717
| | | |
Collapse
|
28
|
Jang DJ, el-Sayed MA. Tryptophan fluorescence quenching as a monitor for the protein conformation changes occurring during the photocycle of bacteriorhodopsin under different perturbations. Proc Natl Acad Sci U S A 1989; 86:5815-9. [PMID: 2762298 PMCID: PMC297721 DOI: 10.1073/pnas.86.15.5815] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The rates of the quenching and recovery of tryptophan fluorescence are determined in the microsecond-millisecond time scale during the photocycle of bacteriorhodopsin under different perturbations. The kinetics suggest the presence of two quenching processes, a rapid one (on the time scale of photocycle intermediate L550 formation or faster) and a slow one (slightly slower than the slow component of intermediate M412 formation). The slow quenching process is found to respond to different perturbations in the same manner as the slow component of M412 formation. It has the same activation energy, it is inhibited if metal cations are removed, it is negligible at pH values greater than the pKa of tyrosine, and its rate is slowed down when 75% of the lipids are removed. These results, together with the observed value of the quenching activation energy, suggest that the rates of the tryptophan fluorescence quenching, like those of tyrosinate and M412 formations during the cycle, are all determined by the rates of the protein conformation changes. The pH studies of the slow quenching process show that the maximum quenching probability occurs at neutral pH. A rapid decrease in quenching occurs at lower pH (approximately 3 and approximately 5.5) and higher pH (approximately 9). Two quenching mechanisms involving energy transfer to either retinal or to tyrosinate are considered. Protein conformation changes resulting from a change in the ionization state of amino acids of different pKa values could change the tryptophan-retinal (or tryptophan-tyrosinate) coupling and thus the quenching efficiency.
Collapse
Affiliation(s)
- D J Jang
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024
| | | |
Collapse
|
29
|
Szundi I, Stoeckenius W. Surface pH controls purple-to-blue transition of bacteriorhodopsin. A theoretical model of purple membrane surface. Biophys J 1989; 56:369-83. [PMID: 2775832 PMCID: PMC1280486 DOI: 10.1016/s0006-3495(89)82683-9] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
We have developed a surface model of purple membrane and applied it in an analysis of the purple-to-blue color change of bacteriorhodopsin which is induced by acidification or deionization. The model is based on dissociation and double layer theory and the known membrane structure. We calculated surface pH, ion concentrations, charge density, and potential as a function of bulk pH and concentration of mono- and divalent cations. At low salt concentrations, the surface pH is significantly lower than the bulk pH and it becomes independent of bulk pH in the deionized membrane suspension. Using an experimental acid titration curve for neutral, lipid-depleted membrane, we converted surface pH into absorption values. The calculated bacteriohodopsin color changes for acidification of purple, and titrations of deionized blue membrane with cations or base agree well with experimental results. No chemical binding is required to reproduce the experimental curves. Surface charge and potential changes in acid, base and cation titrations are calculated and their relation to the color change is discussed. Consistent with structural data, 10 primary phosphate and two basic surface groups per bacteriorhodopsin are sufficient to obtain good agreement between all calculated and experimental curves. The results provide a theoretical basis for our earlier conclusion that the purple-to-blue transition must be attributed to surface phenomena and not to cation binding at specific sites in the protein.
Collapse
Affiliation(s)
- I Szundi
- Cardiovascular Research Institute, University of California, San Francisco 94143
| | | |
Collapse
|
30
|
Lin CT, Chyan YG, Kresheck GC, Bitting HC, el-Sayed MA. Interaction of dibucaine.HCl local anesthetics with bacteriorhodopsin in purple membrane: a spectroscopic study. Photochem Photobiol 1989; 49:641-8. [PMID: 2756000 DOI: 10.1111/j.1751-1097.1989.tb08436.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism.
Collapse
|
31
|
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]
|
32
|
Jang DJ, Corcoran T, El-Sayed MA. EFFECTS OF METAL CATIONS, RETINAL, AND THE PHOTOCYCLE ON THE TRYPTOPHAN EMISSION IN BACTERIORHODOPSIN. Photochem Photobiol 1988. [DOI: 10.1111/j.1751-1097.1988.tb02809.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
33
|
Abstract
The removal of 75% of the lipid from bacteriorhodopsin caused the following: (i) decreased efficiency and rate of deprotonation of the protonated Schiff base (as monitored by absorption of the M412 intermediate); (ii) increased efficiency of deprotonation of deionized samples; (iii) a decrease by 1 unit in the pH at which deprotonation ceases; (iv) increased intensity of Eu3+ emission in Eu3+-regenerated deionized delipidated samples; (v) increased exposure of the Eu3+ sites to water; and (vi) elimination of the dependence of the deprotonation efficiency on the metal cation concentration. These results are discussed in terms of changes in the protein conformation upon delipidation, which in turn control the deprotonation mechanism.
Collapse
Affiliation(s)
- D J Jang
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024
| | | |
Collapse
|
34
|
Relationship between the angular characteristics of a hydrogen bond and the energetics of proton transfer occurring within. J Mol Struct 1988. [DOI: 10.1016/0022-2860(88)80080-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
35
|
|
36
|
Liu SY, Ebrey TG. THE QUANTUM EFFICIENCY FOR THE INTERPHOTOCONVERSION OF THE BLUE and PINK FORMS OF PURPLE MEMBRANE. Photochem Photobiol 1987. [DOI: 10.1111/j.1751-1097.1987.tb04765.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
37
|
Szundi I, Stoeckenius W. Effect of lipid surface charges on the purple-to-blue transition of bacteriorhodopsin. Proc Natl Acad Sci U S A 1987; 84:3681-4. [PMID: 3473476 PMCID: PMC304939 DOI: 10.1073/pnas.84.11.3681] [Citation(s) in RCA: 101] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Purple membrane (lambda max = 568 nm) can be converted to blue membrane (lambda max = 605 nm) by either acid titration or deionization. Partially delipidated purple membrane, containing only 25% of the initial lipid phosphorus, could be converted to a blue form by acid titration but not by deionization. This reversible transition of delipidated membrane did not require the presence of other cations, and the pK of the color change that in native membrane under similar conditions is between 3.0 and 4.0 was shifted to 1.4. We conclude that the purple-to-blue transition is controlled by proton concentration only and that, in native membranes, the cations act only by raising the low surface pH generated by the acidic groups of the lipids. The observation that extraction of lipids from deionized native membrane converts its color from blue to purple further confirms this conclusion. The two states of the membrane probably reflect two preferred conformations of bacteriorhodopsin, which are controlled by protonation changes at the surface of the membrane and differ slightly in the spatial distribution of charges around the chromophore.
Collapse
|