Light-Induced Hydrolysis and Rebinding of Nonisomerizable Bacteriorhodopsin Pigment

Aharoni, Amir; Ottolenghi, Michael; Sheves, Mordechai

doi:10.1016/s0006-3495(02)75603-8

Cited by 10 publications

(15 citation statements)

References 31 publications

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“…To shed further light on the effect of retinal isomerization and the photocycle on the light effect, we studied artificial pigments derived from 13-cis (3)-locked [or all-trans (2)-locked] retinals (Scheme 1), where the critical C 13 AC 14 isomerization is blocked by a 5-membered ring structure (24,25). I-V characteristics similar to those obtained with apo-membranes with retinal oxime are found for those artificial pigments.…”

Section: Resultsmentioning

confidence: 99%

“…Artificial pigments were prepared by reconstituting the apomembrane (suspension in water) with trans-locked and 13-cislocked retinal analogs (24,25), respectively. Briefly, reconstitution was performed by the addition of 25-28 nmol of the retinal analogs and dissolved in 5-10 l of 2-propanol, to yield a 1-ml aqueous suspension of 32 nmol of apo-membrane.…”

Section: Methodsmentioning

confidence: 99%

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Bacteriorhodopsin (bR) as an electronic conduction medium: Current transport through bR-containing monolayers

Jin

Friedman²,

Sheves³

et al. 2006

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

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157

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Studying electron transport (ET) through proteins is hampered by achieving reproducible experimental configurations, particularly electronic contacts to the proteins. The transmembrane protein bacteriorhodopsin (bR), a natural light-activated proton pump in purple membranes of Halobacterium salinarum, is well studied for biomolecular electronics because of its sturdiness over a wide range of conditions. To date, related studies of dry bR systems focused on photovoltage generation and photoconduction with multilayers, rather than on the ET ability of bR, which is understandable because ET across 5-nm-thick, apparently insulating membranes is not obvious. Here we show that electronic current passes through bR-containing artificial lipid bilayers in solid ''electrode-bilayer-electrode'' structures and that the current through the protein is more than four orders of magnitude higher than would be estimated for direct tunneling through 5-nm, water-free peptides. We find that ET occurs only if retinal or a close analogue is present in the protein. As long as the retinal can isomerize after light absorption, there is a photo-ET effect. The contribution of light-driven proton pumping to the steady-state photocurrents is negligible. Possible implications in view of the suggested early evolutionary origin of halobacteria are noted. molecular electronics ͉ vesicles ͉ bioelectronics B acteriorhodopsin (bR) is a protein-chromophore complex that serves as a light-driven proton pump in the purple membrane (PM) of Halobacterium salinarum (1). It has been shown that the protein is composed of seven transmembrane helices with a retinal chromophore covalently bound in the central region via a protonated Schiff base to a lysine residue (Fig. 1A). The PM is organized in a 2D hexagonal crystal lattice with a unit cell dimension of Ϸ6.2 nm. Electron crystallography has indicated that bR is organized into trimers in which lipids mediate intertrimer contact (2). Light absorption by bR initiates a multistep reaction cycle with several distinct spectroscopic intermediates: J 625 , K 590 , L 550 , M 412 , N 560 , and O 640 . More details on the molecular alterations that occur during the photocycle were recently obtained from x-ray diffraction studies (see ref. 3 for a recent review). The light-adapted form of bR contains only all-trans retinal, whereas the dark-adapted form contains a 1:1 mixture of 13-cis and all-trans (4). Because of its long-term stability against thermal, chemical, and photochemical degradation and its desirable photoelectric and photochromic properties, bR has attracted much interest as a material for biooptics and bioelectronics (5). Most of these efforts focused on multilayers and their photovoltage͞photocurrent generation (6-8) and photoconduction (9).In principle, PM patches (Ϸ5 nm thick, a few m in size; see Fig. 1B) can serve as a model protein material that is important for both planar junction fabrication and current transport measurements, because the 5-nm membrane is well beyond the thickness over which tu...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Bacteriorhodopsin (bR) as an electronic conduction medium: Current transport through bR-containing monolayers

Jin

Friedman²,

Sheves³

et al. 2006

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

Self Cite

157

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“…To shed further light on the effect of retinal isomerization and the photocycle on the light effect, we studied artificial pigments derived from 13-cis-(or all-trans)-"locked" retinal, [44] in which the critical C 13 C 14 isomerization is blocked by a fivemember ring structure. [44] Structures of native all-trans retinal and the "locked" analogues used in this study are shown in Scheme 1.…”

Section: Characteristics Of Optoelectronic Responses and Transmembranmentioning

confidence: 99%

“…[44] Structures of native all-trans retinal and the "locked" analogues used in this study are shown in Scheme 1. As shown in Figure 10 (A and B), no photoeffect is seen within experimental error (typically around ± 0.1 nA for a stable junction).…”

Section: Characteristics Of Optoelectronic Responses and Transmembranmentioning

confidence: 99%

Bacteriorhodopsin‐Monolayer‐Based Planar Metal–Insulator–Metal Junctions via Biomimetic Vesicle Fusion: Preparation, Characterization, and Bio‐optoelectronic Characteristics

Jin

Friedman

Sheves

et al. 2007

Adv Funct Materials

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A reliable and reproducible method for preparing bacteriorhodopsin (bR)‐containing metal–biomolecule–monolayer‐metal planar junctions via vesicle fusion tactics and soft deposition of Au top electrodes is reported. Optimum monolayer and junction preparations, including contact effects, are discussed. The electron‐transport characteristics of bR‐containing membranes are studied systematically by incorporating native bR or artificial bR pigments derived from synthetic retinal analogues, into single solid‐supported lipid bilayers. Current–voltage (I–V) measurements at ambient conditions show that a single layer of such bR‐containing artificial lipid bilayers pass current in solid electrode/bilayer/solid electrode structures. The current is passed only if retinal or its analogue is present in the protein. Furthermore, the preparations show photoconductivity as long as the retinal can isomerize following light absorption. Optical characterization suggests that the junction photocurrents might be associated with a photochemically induced M‐like intermediate of bR. I–V measurements along with theoretical estimates reveal that electron transfer through the protein is over four orders of magnitude more efficient than what would be estimated for direct tunneling through 5 nm of water‐free peptides. Our results furthermore suggest that the light‐driven proton‐pumping activity of the sandwiched solid‐state bR monolayer contributes negligibly to the steady‐state light currents that are observed, and that the orientation of bR does not significantly affect the observed I–V characteristics.

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“…11 The effects of the osmotically active solutes on the PM structure have been previously studied by applying an osmotic pressure that can withdraw the aforementioned water molecules from the protein interior, distort the protein landscape, and therefore, alter the local environment and the chromophoreprotein interactions. 66,67 As shown in Figure 4a, a solution of 33% regenerated pigment (A 33% , AOO) in phosphate buffer, l max 557 nm, exhibits a monophasic positive CD at 547 nm; however, upon centrifugation and resuspension of the precipitated pellet in 50% sucrose, the CD undergoes a sign inversion exhibiting a single negative CE at 592 nm (under both conditions, the UV -vis is maintained at 561 nm; data not shown). The CD curves in buffer and sucrose can be reversibly interchanged upon repetition of the centrifugation/resuspension sequence, confirming reversible conformational changes upon solute-induced distortion.…”

mentioning

confidence: 90%

Circular dichroism of heterochromophoric and partially regenerated purple membrane: Search for exciton coupling

et al. 2005

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In order to determine the origin of the bisignate CD spectra of native purple membrane, heterochromophoric analogues containing bacteriorhodopsin regenerated with native all-trans-retinal and retinal analogues were investigated. The data collected for the purple membrane samples containing two different chromophores suggest the additive character of the CD spectra. This conclusion was supported by a series of spectra using 5,6-dihydroretinal and 3-dehydroretinal and by using 33% regenerated PM in buffer and in presence of osmolytes. Our results support the idea of conformational heterogeneity of the chromophores in the bR in the trimer, suggesting that the three bR subunits in the trimer are not conformationally equal, and therefore, the bisignate CD spectrum of bR in the purple membrane occurs rather due to a superposition of the CD spectra from variously distorted bR subunits in the trimer than interchromophoric exciton-coupling interactions.

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Light-Induced Hydrolysis and Rebinding of Nonisomerizable Bacteriorhodopsin Pigment

Cited by 10 publications

References 31 publications

Bacteriorhodopsin (bR) as an electronic conduction medium: Current transport through bR-containing monolayers

Bacteriorhodopsin (bR) as an electronic conduction medium: Current transport through bR-containing monolayers

Bacteriorhodopsin‐Monolayer‐Based Planar Metal–Insulator–Metal Junctions via Biomimetic Vesicle Fusion: Preparation, Characterization, and Bio‐optoelectronic Characteristics

Circular dichroism of heterochromophoric and partially regenerated purple membrane: Search for exciton coupling

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