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Perálvarez-Marín A, Sepulcre F, Márquez M, Proietti MG, Padrós E. Combination of extended X-ray absorption fine structure spectroscopy with lipidic cubic phases for the study of cation binding in bacteriorhodopsin. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 40:1007-12. [PMID: 21667310 DOI: 10.1007/s00249-011-0714-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 05/10/2011] [Accepted: 05/18/2011] [Indexed: 10/18/2022]
Abstract
We have performed a quantitative X-ray absorption fine structure analysis of bacteriorhodopsin in purple membrane patches and in lipidic cubic phases regenerated with Mn(2+). Lipidic cubic phases and purple membrane results have been compared, demonstrating that the lipidic cubic phase process does not introduce relevant distortions in the local geometry of the cation binding sites. For both samples, we have observed similarities for Mn(2+) coordination in terms of type, number, and average distances of surrounding atoms, indicating a first coordination shell composed by 6 O atoms, and 3/4 C atoms located in the second coordination shell.
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Affiliation(s)
- Alex Perálvarez-Marín
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, Bellaterra, Spain.
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2
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Heyes CD, El-Sayed MA. Proton transfer reactions in native and deionized bacteriorhodopsin upon delipidation and monomerization. Biophys J 2003; 85:426-34. [PMID: 12829497 PMCID: PMC1303098 DOI: 10.1016/s0006-3495(03)74487-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
We have investigated the role of the native lipids on bacteriorhodopsin (bR) proton transfer and their connection with the cation-binding role. We observe that both the efficiency of M formation and the kinetics of M rise and decay depend on the lipids and lattice but, as the lipids are removed, the cation binding is a much less important factor for the proton pumping function. Upon 75% delipidation using 3-[(cholamidopropyl)dimethylammonio]-propanesulfonate (CHAPS), the M formation and decay kinetics are much slower than the native, and the efficiency of M formation is approximately 30%-40% that of the native. Upon monomerization of bR by Trition X-100, the efficiency of M recovers close to that of the native (depending on pH), M formation is approximately 10 times faster, and M decay kinetics are comparable to native at pH 7. The same results on the M intermediate are observed if deionized blue bR (deI bbR) is treated with these detergents (with or without pH buffers present), even though deionized blue bR containing all the lipids has no photocycle. This suggests that the cation(s) has a role in native bR that is different than in delipidated or monomerized bR, even so far as to suggest that the cation(s) becomes unimportant to the function as the lipids are removed.
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Affiliation(s)
- Colin D Heyes
- Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
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3
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Taneva SG, Goñi FM, Tuparev NP, Petkanchin I, Dér A, Muga A. Effect of Asp85 replacement by Thr on the conformation, surface electric properties and stability of bacteriorhodopsin. Colloids Surf A Physicochem Eng Asp 2002. [DOI: 10.1016/s0927-7757(02)00180-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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4
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Heyes CD, El-Sayed MA. The role of the native lipids and lattice structure in bacteriorhodopsin protein conformation and stability as studied by temperature-dependent Fourier transform-infrared spectroscopy. J Biol Chem 2002; 277:29437-43. [PMID: 12058039 DOI: 10.1074/jbc.m203435200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report the effect of partial delipidation and monomerization on the protein conformational changes of bacteriorhodopsin (bR) as a function of temperature. Removal of up to 75% of the lipids is known to have the lattice structure of the purple membrane, albeit as a smaller unit cell, whereas treatment by Triton monomerizes bR into micelles. The effects of these modifications on the protein secondary structure is analyzed by monitoring the protein amide I and amide II bands in the Fourier transform-infrared (FT-IR) spectra. It is found that removal of the first 75% of the lipids has only a slight effect on the secondary structure at physiological temperature, whereas monomerizing bR into micelles alters the secondary structure considerably. Upon heating, the bR monomer is found to have a very low thermal stability compared with the native bR with its melting point reduced from 97 to 65 degrees C, and the pre-melting transition in which the protein changes conformation in native bR at 80 degrees C could not be observed. Also, the N[bond]H to N[bond]D exchange of the amide II band is effectively complete at room temperature, suggesting that there are no hydrophobic regions that are protected from the aqueous medium, possibly explaining the low thermal stability of the monomer. On the other hand, 75% delipidated bR has its melting temperature close to that of the native bR and does have a pre-melting transition, although the pre-melting transition occurs at significantly higher temperature than that of the native bR (91 degrees C compared with 80 degrees C) and is still reversible. Furthermore, we have also observed that the reversibility of this pre-melting transition of both native and partially delipidated bR is time-dependent and becomes irreversible upon holding at 91 degrees C between 10 and 30 min. These results are discussed in terms of the lipid and lattice contribution to the protein thermal stability of native bR.
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Affiliation(s)
- Colin D Heyes
- Laser Dynamics Laboratory, School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
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5
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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.
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Affiliation(s)
- Colin D Heyes
- Laser Dynamics Lab, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
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6
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Sanz C, Márquez M, Perálvarez A, Elouatik S, Sepulcre F, Querol E, Lazarova T, Padrós E. Contribution of extracellular Glu residues to the structure and function of bacteriorhodopsin. Presence of specific cation-binding sites. J Biol Chem 2001; 276:40788-94. [PMID: 11524418 DOI: 10.1074/jbc.m104836200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Single and multiple mutants of extracellular Glu side chains of bacteriorhodopsin were analyzed by acid and calcium titration, differential scanning calorimetry, and thermal difference spectrophotometry. Acid titration spectra show that the second group protonating with Asp(85) is revealed in E204Q in the absence of Cl(-) but is not observed in the triple mutant E9Q/E194Q/E204Q or in the quadruple mutant E9Q/E74Q/E194Q/E204Q. The results point to Glu(9) as the second group protonating cooperatively with Asp(85). Comparison of the apparent pK(a) of Asp(85) protonation in water and in the deionized forms and results of calcium titration suggest that cation-binding sites are of low affinity in the multiple Glu mutants. Like for deionized wild type bacteriorhodopsin, differential scanning calorimetry reveals a lack of the pretransition in the multiple mutants, whereas in E9Q it appears at lower temperature and with lower cooperativity. Additionally, at neutral pH the band at 630 nm arising from cation release upon temperature increase is absent for the multiple mutants. Based on these results, we propose the presence of two cation-binding sites in the extracellular region of bacteriorhodopsin having as ligands Glu(9), Glu(194), Glu(204), and water molecules.
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Affiliation(s)
- C Sanz
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Barcelona 08193, Spain
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7
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Wang G, Hu KS. Effects of pH and acetylation on Hg(2+)-induced purple to blue transition in bacteriorhodopsin. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2001; 60:97-101. [PMID: 11470564 DOI: 10.1016/s1011-1344(01)00126-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Effects of Hg(2+) ions on the absorption spectrum of bacteriorhodopsin have been measured at different pH values and after acetylation. UV-difference spectroscopy and CD spectra show that Hg(2+)-induced color change is essentially similar to that caused by removal of cations or acidification. The ability of Hg(2+)-induced purple-to-blue transition is pH-dependent and exhibits a maximum at pH 5.5. Acetylation influences the absorption in the same way as Hg(2+) ions and accelerates Hg(2+)-induced purple to blue transition. All these results strongly suggest that the Hg(2+) effect is not a specific binding but just a replacement of intrinsic cations on the membrane surface, where they form a double layer. The composition of the double layer determines the surface pH on the membrane, which affects the color of the bacteriorhodopsin.
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Affiliation(s)
- G Wang
- Institute of Biophysics, Academia Sinica, 15 Datun Road, 100101, Beijing, China
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8
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Kimura S, Naito A, Tuzi S, Saitô H. A (13)C NMR study on [3-(13)C]-, [1-(13)C]Ala-, or [1-(13)C]Val-labeled transmembrane peptides of bacteriorhodopsin in lipid bilayers: insertion, rigid-body motions, and local conformational fluctuations at ambient temperature. Biopolymers 2001; 58:78-88. [PMID: 11072231 DOI: 10.1002/1097-0282(200101)58:1<78::aid-bip80>3.0.co;2-c] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
We have recorded (13)C NMR spectra of selectively [3-(13)C]Ala-, [1-(13)C]Ala-, or [1-(13)C]Val-labeled synthetic transmembrane peptides of bacteriorhodopsin (bR) and enzymatically cleaved C-2 fragment in the solid and dimyristoylphosphatidylcholine bilayer. It turned out that these transmembrane peptides either in hexafluoroisopropanol or cast from it take an ordinary alpha-helix (alpha(I)-helix) irrespective of their amino acid sequences with reference to the conformation-dependent (13)C chemical shifts of (Ala)(n) taking the alpha-helix form. These transmembrane peptides are not always static in the lipid bilayer as in the solid state but undergo rigid-body motions with various frequencies as estimated from suppressed peaks either by fast isotropic or large-amplitude motions (>10(8) Hz) or intermediate frequencies (10(5) or 10(3) Hz). Further, (13)C chemical shifts of the [3-(13)C]Ala-labeled peptides in the bilayer were displaced downfield by 0.3-1.1 ppm depending upon amino acid sequence with respect to those in the solid state, which were explained in terms of local conformational fluctuation (10(2) Hz) deviated from the torsion angles (alpha(II)-helix) from those of standard alpha-helix, under anisotropic environment in lipid bilayer, in addition to the above-mentioned rigid-body motions. The carbonyl (13)C peaks, on the other hand, are not sensitively displaced by such local anisotropic fluctuations, because they are more sensitive to the manner of hydrogen-bond interactions. The amino acid sequences of these peptides inserted within the bilayer were not always the same as those of intact bR, causing disposition of the transmembrane alpha-helical segment from that of intact bR. Finally, we confirmed that the (13)C NMR peak positions of the random coil form are located at the boundary between the alpha-helix and a turned structure in loop regions.
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Affiliation(s)
- S Kimura
- Department of Life Science, Faculty of Science, Harima Science Garden City, Kouto 3-chome, Kamigori, Hyogo 678-1297, Japan
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9
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Lewis RN, McElhaney RN. Calorimetric and spectroscopic studies of the thermotropic phase behavior of lipid bilayer model membranes composed of a homologous series of linear saturated phosphatidylserines. Biophys J 2000; 79:2043-55. [PMID: 11023908 PMCID: PMC1301094 DOI: 10.1016/s0006-3495(00)76452-6] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The thermotropic phase behavior of lipid bilayer model membranes composed of the even-numbered, N-saturated 1,2-diacyl phosphatidylserines was studied by differential scanning calorimetry and by Fourier-transform infrared and (31)P-nuclear magnetic resonance spectroscopy. At pH 7.0, 0.1 M NaCl and in the absence of divalent cations, aqueous dispersions of these lipids, which have not been incubated at low temperature, exhibit a single calorimetrically detectable phase transition that is fully reversible, highly cooperative, and relatively energetic, and the transition temperatures and enthalpies increase progressively with increases in hydrocarbon chain length. Our spectroscopic observations confirm that this thermal event is a lamellar gel (L(beta))-to-lamellar liquid crystalline (L(alpha)) phase transition. However, after low temperature incubation, the L(beta)/L(alpha) phase transition of dilauroyl phosphatidylserine is replaced by a higher temperature, more enthalpic, and less cooperative phase transition, and an additional lower temperature, less enthalpic, and less cooperative phase transition appears in the longer chain phosphatidylserines. Our spectroscopic results indicate that this change in thermotropic phase behavior when incubated at low temperatures results from the conversion of the L(beta) phase to a highly ordered lamellar crystalline (L(c)) phase. Upon heating, the L(c) phase of dilauroyl phosphatidylserine converts directly to the L(alpha) phase at a temperature slightly higher than that of its original L(beta)/L(alpha) phase transition. Calorimetrically, this process is manifested by a less cooperative but considerably more energetic, higher-temperature phase transition, which replaces the weaker L(beta)/L(alpha) phase transition alluded to above. However, with the longer chain compounds, the L(c) phase first converts to the L(beta) phase at temperatures some 10-25 degrees C below that at which the L(beta) phase converts to the L(alpha) phase. Our results also suggest that shorter chain homologues form L(c) phases that are structurally related to, but more ordered than, those formed by the longer chain homologues, but that these L(c) phases are less ordered than those formed by other phospholipids. These studies also suggest that polar/apolar interfaces of the phosphatidylserine bilayers are more hydrated than those of other glycerolipid bilayers, possibly because of interactions between the polar headgroup and carbonyl groups of the fatty acyl chains.
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Affiliation(s)
- R N Lewis
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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10
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Tuzi S, Yamaguchi S, Tanio M, Konishi H, Inoue S, Naito A, Needleman R, Lanyi JK, Saitô H. Location of a cation-binding site in the loop between helices F and G of bacteriorhodopsin as studied by 13C NMR. Biophys J 1999; 76:1523-31. [PMID: 10049332 PMCID: PMC1300128 DOI: 10.1016/s0006-3495(99)77311-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The high-affinity cation-binding sites of bacteriorhodopsin (bR) were examined by solid-state 13C NMR of samples labeled with [3-13C]Ala and [1-13C]Val. We found that the 13C NMR spectra of two kinds of blue membranes, deionized (pH 4) and acid blue at pH 1.2, were very similar and different from that of the native purple membrane. This suggested that when the surface pH is lowered, either by removal of cations or by lowering the bulk pH, substantial change is induced in the secondary structure of the protein. Partial replacement of the bound cations with Na+, Ca2+, or Mn2+ produced additional spectral changes in the 13C NMR spectra. The following conclusions were made. First, there are high-affinity cation-binding sites in both the extracellular and the cytoplasmic regions, presumably near the surface, and one of the preferred cation-binding sites is located at the loop between the helix F and G (F-G loop) near Ala196, consistent with the 3D structure of bR from x-ray diffraction and cryoelectron microscopy. Second, the bound cations undergo rather rapid exchange (with a lifetime shorter than 3 ms) among various types of cation-binding sites. As expected from the location of one of the binding sites, cation binding induced conformational alteration of the F-G interhelical loop.
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Affiliation(s)
- S Tuzi
- Department of Life Science, Himeji Institute of Technology, Harima Science Garden City, Kamigori, Hyogo, Japan 678-1297, USA
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11
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Tanio M, Tuzi S, Yamaguchi S, Konishi H, Naito A, Needleman R, Lanyi JK, Saitô H. Evidence of local conformational fluctuations and changes in bacteriorhodopsin, dependent on lipids, detergents and trimeric structure, as studied by 13C NMR. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1375:84-92. [PMID: 9767127 DOI: 10.1016/s0005-2736(98)00151-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We examined how the local conformation and dynamics of [3-13C]Ala-labeled bacteriorhodopsin (bR) are altered as viewed from 13C NMR spectra when the natural membrane lipids are partly or completely replaced with detergents. It turned out that the major conformational features of bR, the alphaII-helices, are generally unchanged in the delipidated or solubilized preparations. Upon partial delipidation or detergent solubilization, however, a significant conformational change occurs, ascribed to local conversion of alphaII-->alphaI-helix (one Ala residue involved), evident from the upfield displacement of the transmembrane helical peak from 16.4 ppm to 14.5 ppm, conformational change (one or two Ala residues) within alphaII-helices from 16.4 to 16.0 ppm, and acquired flexibility in the loop region (especially at the F-G loop) as manifested from suppressed peak-intensities in cross-polarization magic angle spinning (CP-MAS) NMR spectra. On the other hand, formation of monomers as solubilized by Triton X-100, Triton N-101 and n-dodecylmaltoside is characterized by the presence of a peak at 15.5 ppm and a shifted absorption maximum (550 nm). The size of micelles under the first two conditions was small enough to yield 13C NMR signals observable by a solution NMR spectrometer, although 13C CP-MAS NMR signals were also visible from a fraction of large-sized micelles. We found that the 16.9 ppm peak (three Ala residues involved), visible by CP-MAS NMR, was displaced upfield when Schiff base was removed by solubilization with sodium dodecyl sulfate, consistent with our previous finding of bleaching to yield bacterioopsin.
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Affiliation(s)
- M Tanio
- Department of Life Science, Himeji Institute of Technology, Hyogo 678-1297, Japan
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12
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Pardo L, Sepulcre F, Cladera J, Duñach M, Labarta A, Tejada J, Padrós E. Experimental and theoretical characterization of the high-affinity cation-binding site of the purple membrane. Biophys J 1998; 75:777-84. [PMID: 9675179 PMCID: PMC1299752 DOI: 10.1016/s0006-3495(98)77567-8] [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: 11/17/2022] Open
Abstract
Binding of Mn2+ or Mg2+ to the high-affinity site of the purple membrane from Halobacterium salinarium has been studied by superconducting quantum interference device magnetometry or by ab initio quantum mechanical calculations, respectively. The binding of Mn2+ cation, in a low-spin state, to the high-affinity site occurs through a major octahedral local symmetry character with a minor rhombic distortion and a coordination number of six. A molecular model of this binding site in the Schiff base vicinity is proposed. In this model, a Mg2+ cation interacts with one oxygen atom of the side chain of Asp85, with both oxygen atoms of Asp212 and with three water molecules. One of these water molecules is hydrogen bonded to both the nitrogen of the protonated Schiff base and the Asp85 oxygen. It could serve as a shuttle for the Schiff base proton to move to Asp85 in the L-M transition.
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Affiliation(s)
- L Pardo
- Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
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13
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Cladera J, Torres J, Padrós E. Analysis of conformational changes in bacteriorhodopsin upon retinal removal. Biophys J 1996; 70:2882-7. [PMID: 8744326 PMCID: PMC1225268 DOI: 10.1016/s0006-3495(96)79858-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The conformation of bacterioopsin in the apomembrane has been studied by Fourier transform infrared spectroscopy. Resolution enhancement techniques and curve-fitting procedures have been used to determine the secondary structural components from the amide I region. Bacterioopsin contains about 54% helicoidal structure (alpha I and alpha II helices + 3(10) turns), 21% sheets, 16% reverse turns, and 9% unordered structure. Thus, after retinal removal, all of the secondary structural types of bacteriorhodopsin remain present, and only slight quantitative differences appear. On the other hand, H/D exchange studies show that there is a higher degree of exchange for reverse turns and protonated carboxylic lateral chains in bacterioopsin as compared to bacteriorhodopsin. This gives further support to the idea of a more open tertiary structure of bacterioopsin, and to the consideration of the retinal molecule as an important element in complementing the interhelical interactions in bacteriorhodopsin folding.
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Affiliation(s)
- J Cladera
- Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Spain
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14
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Stuart JA, Vought BW, Zhang CF, Birge RR. The active site of bacteriorhodopsin. Two-photon spectroscopic evidence for a positively charged chromophore binding site mediated by calcium. ACTA ACUST UNITED AC 1995. [DOI: 10.1002/bspy.350010104] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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15
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Tuzi S, Naito A, Saitô H. 13C NMR study on conformation and dynamics of the transmembrane alpha-helices, loops, and C-terminus of [3-13C]Ala-labeled bacteriorhodopsin. Biochemistry 1994; 33:15046-52. [PMID: 7999762 DOI: 10.1021/bi00254a013] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have recorded 13C CP-MAS and DD-MAS NMR spectra of untreated and deionized [3-13C]-Ala-labeled bacteriorhodopsin (bR) and those cleaved with carboxypeptidase A and papain to gain insight into the conformation and dynamics of the transmembrane alpha-helices, loops, and C-terminus. It turned out that the C-terminus does not contribute to the 13C CP-MAS NMR spectra of [3-13C]Ala-bR recorded at ambient temperature owing to its rapid reorientational motions, since the relative peak intensities were unchanged in spite of the enzymatic cleavages. Therefore, the 13C CP-MAS NMR peaks of bR should be ascribed both to the transmembrane alpha-helices and loops. We further distinguished the peaks of the alpha II-helix form at 16.3 ppm (60%) from those of the alpha I-helix form at 14.9 ppm (20%) by deconvolution of the respective peaks of the hydrated [3-13C]Ala-bR, as referred to the 13C chemical shift of polyalanine in hexafluoroisopropyl alcohol. The remaining CP-MAS NMR peak of [3-13C]Ala-bR at 17.2 ppm was ascribed to the loops (20%) taking a variety of turn structures. In contrast, the 13C NMR signals from the C-terminal residues were significantly enhanced by recording the dipolar-decoupled (DD)-MAS NMR spectra. Conformational features of the two different portions of the C-terminus, residues 245-248 and 231-244, were revealed by the conformation-dependent 13C signals of bR successively cleaved by carboxypeptidase A and papain, respectively. The terminal end, residues 245-248, containing two Ala residues is virtually disordered and undergoing rapid motions.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S Tuzi
- Department of Life Science, Himeji Institute of Technology, Hyogo, Japan
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16
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Cladera J, Galisteo ML, Sabés M, Mateo PL, Padrós E. The role of retinal in the thermal stability of the purple membrane. EUROPEAN JOURNAL OF BIOCHEMISTRY 1992; 207:581-5. [PMID: 1633811 DOI: 10.1111/j.1432-1033.1992.tb17084.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Differential scanning calorimetry demonstrates that the bleached form of the purple membrane does not possess any measurable thermal transition in water, up to 105 degrees C, whereas in 0.1 M phosphate pH 7.5 it shows a transition at about 82 degrees C, with an enthalpy of 110 kJ/mol. In the latter medium, the native membrane shows the main transition at 97 degrees C, with an enthalpy of 390 kJ/mol. The reduced form of the purple membrane shows two small transitions in water, as well as in 0.1 M phosphate, which do not seem to be related to the main thermal transition of the native membrane. Fourier-transform infrared spectra in D2O show that the two modified samples, as well as the native one, undergo similar secondary structural changes upon thermal denaturation. These changes appear to extend through a wide temperature range for both modified forms, particularly for the bleached one. The results suggest that the main thermal transition in the purple membrane is due to a cooperative conformational change involving the disruption of the network of electrostatic and hydrogen-bonding interactions which originate from the protonated Schiff base. In the two modified membranes, these conformational changes appear to proceed smoothly through a rather low or non-cooperative process. The thermal behaviour of the bleached membrane in water resembles that of the molten globule state described for several globular proteins.
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Affiliation(s)
- J Cladera
- Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Spain
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17
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Draheim JE, Gibson NJ, Cassim JY. Dramatic in situ conformational dynamics of the transmembrane protein bacteriorhodopsin. Biophys J 1991; 60:89-100. [PMID: 1883946 PMCID: PMC1260041 DOI: 10.1016/s0006-3495(91)82033-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The conformational dynamic capabilities of the in situ bacteriorhodopsin (bR) can be studied by determination of the changes of the bR net helical segmental tilt angle (the angle between the polypeptide segments and the membrane normal) induced by various perturbations of the purple membrane (PM). The analysis of the far-UV oriented circular dichroism (CD) of the PM provides one means of achieving this. Previous CD studies have indicated that the tilt angle can change from approximately 10 degrees to 39 degrees depending on the perturbants used with no changes in the secondary structure of the bR. A recent study has indicated that the bleaching-induced tilt angle can be enhanced from approximately 24 degrees to 39 degrees by cross-linkage and papain-digestion perturbations which by themselves do not alter the tilt angle. To add further credence, this study has been repeated using midinfrared (IR) linear dichroic spectral analysis. In contrast to the CD method, analysis by the IR method depends on the orientation of the amide plane of the helix assumed. Excellent consistency is achieved between the two methods only when it is assumed that the structural characteristics of the alpha-helices of the bR are equally alpha I and alpha II in nature. Furthermore, the analysis of the IR data becomes essentially independent of the three amide transitions utilized. The net tilt angle of segments completely randomized relative to the incident light must be 54.736 in view of helix symmetry. A value of 54.735 degrees +/- 0.001 degree was achieved by the IR method for the ethanol-treated PM film, establishing this kind of film as an ideal random state standard and demonstrating the accuracy potential of the IR method.
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Affiliation(s)
- J E Draheim
- Department of Chemistry, Adrian College, Michigan 49221
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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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