Electric field induced conformational changes of bacteriorhodopsin in purple membrane films

Tsuji, Kinko; Hess, Benno

doi:10.1007/bf00254209

Cited by 21 publications

(10 citation statements)

References 29 publications

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“…The voltage dependence of the amplitude of the electroabsorption spectrum in oriented D85N films is quadratic, with a threshold (Fig. 3), as seen in previous measurements on oriented and unoriented wild-type films (7,8). At the highest applied voltages, the fractional absorption change at 600 nm is -25% and can be seen by eye.…”

supporting

confidence: 80%

“…This produced films of moderate optical quality. High-opticalquality, oriented samples, in which a majority of the patches were aligned with their cytoplasmic side facing the substrate, were deposited on the same type of slide by using the technique of electrophoretic sedimentation (4,7,8). Optically thick wild-type BR films made in this manner exhibited photovoltages of typically 11.5 V upon illumination by yellow light of intensity 0.15 W/cm2, indicating a high degree of orientation of the constituent membrane patches.…”

Section: Introductionmentioning

confidence: 99%

“…Application of an external field to films ofwild-type BR induces spectroscopic changes that are unrelated to the protonation state of the Schiff base (7,8). However, there are several mutants and retinal-analogsubstituted variants of BR in which the Schiff-base proton is much more weakly bound, as indicated by pK values in the range 7 to 9 (9)(10)(11)(12).…”

mentioning

confidence: 99%

“…This produced films of moderate optical quality. High-opticalquality, oriented samples, in which a majority of the patches were aligned with their cytoplasmic side facing the substrate, were deposited on the same type of slide by using the technique of electrophoretic sedimentation (4,7,8 The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.…”

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Electric-field-induced Schiff-base deprotonation in D85N mutant bacteriorhodopsin.

Kolodner¹,

Лукашев²,

Ching³

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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The application of an external electric field to dry films of Asp-85 --Asn mutant bacteriorhodopsin causes deprotonation of the Schiff base, resulting in a shift of the optical absorption maximum from 600 nm to 400 nm. This is in marked contrast to the case of wild-type bacteriorhodopsin films, in which electric fields produce a red-shifted product whose optical properties are similar to those of the acid-blue form of the protein. This difference is due to the much weaker binding of the Schiff-base proton in the mutant protein, as indicated by its low pK of -9, as compared with the value pK 13 in the wild type. Other bacteriorhodopsins with lowered Schiff-base pK values should also exhibit a fieldinduced shift in the protonation equilibrium ofthe Schiffbase. We propose mechanisms to account for these observations. mutant bacteria with the Asp-85 --Asn (D85N) mutation (10),we have discovered that external electric fields cause reversible spectroscopic changes which unambiguously represent Schiffbase deprotonation. Explaining the mechanism of this deprotonation will require the application of recently developed numerical techniques of minimization of the electrostatic energy of the protein and may impose new constraints on its structure (13). In addition, this observation may have great technological significance: it may be possible to exploit the effect, using genetic and/or chemical modification of BR, to produce unique electrochromic materials-"electronic ink"-with important applications in the technology of reflective displays.Bacteriorhodopsin (BR) is a protein found in the cell membrane of the bacterium Halobacterium salinarium. BR consists of seven a-helices which span the membrane, forming a channel through which protons can be transported. Upon absorption of a photon, BR undergoes a photocycle which results in the translocation of a proton across the membrane, converting the free energy of the photon into chemical energy for metabolism (1, 2). BR can be isolated from the bacterium in the form of purple membranes (3)-so called because of a strong absorption band centered at 570 nm-in which trimers of BR molecules are incorporated in patches of lipid bilayer. These patches can be assembled into dry films for experimentation (4). The deep purple color of BR comes from the chromophore retinal, which is bound to a lysine residue inside the membrane channel via a protonated Schiff-base linkage. Unbound retinal in solution is faintly yellow, exhibiting a strong absorption centered at 360 nm. However, upon incorporation into BR, the retinal absorption band center shifts to 570 nm. This opsin shift is caused in large part by charge redistribution in the retinal due to the positive charge of the proton at the Schiff base. Deprotonation of the Schiff base during the M intermediate state of the BR photocycle leads to a transient partial abolition of the opsin shift, switching the absorption maximum from 570 nm to 410 nm (1, 2). BR variants in which the lifetime of the deprotonated state is prolonged by chemic...

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supporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

“…This produced films of moderate optical quality. High-opticalquality, oriented samples, in which a majority of the patches were aligned with their cytoplasmic side facing the substrate, were deposited on the same type of slide by using the technique of electrophoretic sedimentation (4,7,8 The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.…”

mentioning

confidence: 99%

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Electric-field-induced Schiff-base deprotonation in D85N mutant bacteriorhodopsin.

Kolodner¹,

Лукашев²,

Ching³

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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“…The fields perpendicular to the membrane plane, which are related to the membrane potentials, influence directly the biological activity of the membrane proteins including ion channel gating (I, 2) proton translocation (3), and enzymatic activity (4-6). The effect of membrane potential on the biological activity is assumed to be through its effect on the conformation of the membrane proteins.…”

Section: Membranementioning

confidence: 99%

Conformation and Mobility of Membrane Proteins in Electric Fields

Miller

Brumfeld

Korenstein

1994

Advances in Chemistry

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Electric fields affect the movement and the conformation of membrane proteins and channel forming polypeptides in the membrane. Diffu sion potentials, created by a potassium concentration gradient across the membrane in the presence of valinomycin, affect the circular dichroism (CD) of bacteriorhodopsin reconstituted in lipid vesicles. The changes in CD indicate that the applied electric field, irrespective of its direction, decreases the helical fraction and increases the frac tions of the random and β structures. Donnan potentials, created across the vesicular bilayer membrane by polyelectrolytes, are used to induce the conformational changes in alamethicin. The induced change of CD by the electric field across the membrane was not symmetrical with respect to the field direction. Tangential electric fields induce lateral movements of membrane components. The eletrophoretic move ment of photosystem I (PSI) along the membrane of hypotonically swollen thylakoid vesicles induced by low electric fields (40-80 V/cm) is studied by analyzing its electrophotoluminescence (EPL) from the different poles of the vesicle. The average apparent electric mobility, determined from the time course of the increase of EPL on the enriched hemisphere and of the decrease of EPL on the depleted hemisphere, was of the order of 3.10-5 cm 2 /(V s). The distribution of PSI reaches a steady state when the diffusional, electrostatic, and other counteracting forces balance the electrophoretic driving force. The electrophoretic mobility obtained from the steady state conditions 0065-2393/94/0235-0107$08.54/0

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Electric Field Induced Structure Changes in Nonionic Water‐in‐Oil Microemulsions: Field Dependence of the Electric Conductivity

Runge

Röhl

Ilgenfritz

1991

Ber Bunsenges Phys Chem

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Colloides / Electric Field / Electrical Properties / Microemulsions / Percolation Water-in-oil microcmulsions, stabilized by the nonionic surfactant Igepal CO-520, show a temperature dependent structure change which can be monitored by electric conductivity. We show that the transition which involves the percolation of the aqueous phase can also be induced by high electric fields. A system is investigated which contains only a few volume percent of the aqueous phase (0.1 M KCI) in a mixture of n-and c-hexanc but still exhibits a highly cooperative transition from the conducting state at lower temperature to the almost nonconducting state at highcr temperature. Electric fields, applied up to ca. 10 k V cm-', shift the transition curves to the high temperature side, i.e. restore a structure with continuous water channels. The percolation point exhibits a quadratic field strength dependence. The dynamics of the transition in the micro-to millisecond range shows characteristic differences below and above the percolation point. The transient behavior and the electric field strength dependence of the conductivity change are discussed with respect to a theory [9] developed for ionic microemulsions. -A special field pulse method is described which allows measurement of current relaxation and electric birefringence.

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Electric field induced conformational changes of bacteriorhodopsin in purple membrane films

Cited by 21 publications

References 29 publications

Electric-field-induced Schiff-base deprotonation in D85N mutant bacteriorhodopsin.

Electric-field-induced Schiff-base deprotonation in D85N mutant bacteriorhodopsin.

Conformation and Mobility of Membrane Proteins in Electric Fields

Electric Field Induced Structure Changes in Nonionic Water‐in‐Oil Microemulsions: Field Dependence of the Electric Conductivity

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