Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin

Chang, Chung‐Ho; Govindjee, Rajni; Ebrey, Thomas G.; Bagley, Kimberly A.; Dollinger, Gavin; Eisenstein, L.; Marque, Jeffrey; Röder, Heinrich; Vittitow, J.; Fang, Jim‐Min

doi:10.1016/s0006-3495(85)83944-8

Cited by 49 publications

(33 citation statements)

References 9 publications

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“…I-V characteristics similar to those obtained with apo-membranes with retinal oxime are found for those artificial pigments. The lack of photoeffect in junctions made with apo-membranes is in keeping with the absence of a photocycle in these samples (24,26), supporting the hypothesis that occurrence of retinal isomerization is a prerequisite for the light effect. We assume that no pronounced, electric-field-induced, bR conformational change occurs (i.e., bR will remain native-like) in the Յ10 6 V͞cm fields across the protein that are reached in our experiments.…”

Section: Resultssupporting

confidence: 76%

“…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.

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: Resultssupporting

confidence: 76%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

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.

157

View full text Add to dashboard Cite

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“…It is not a visual pigment but a light-driven proton pump [2]. The function is initiated by the all-trans--* 13-cis photoisomerization of retinal [3]. The primary step is an efficient, selective, and ultrafast isomerization.…”

Section: Introductionmentioning

confidence: 99%

Fluorescence spectra of bacteriorhodopsin and the intermediates O and Q at room temperature

et al. 1995

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“…There are, however, some basic structural differences between the systems. For the visual process the chromophore is the 11-cis retinal, whereas in bacteriorhodopsin, the chromophore is the all-trans retinal (10). For bacteriorhodopsin, the primary event is believed to be an all-trans to 13-cis isomerization and like invertebrates, the chromophore does not detach from the opsin during the photocycle.…”

Section: Introductionmentioning

confidence: 99%

Effect of protonation on the ground state properties of retinal analogs: an ab-initio study

Poirier¹,

Yadav²,

Śurján³

1987

Can. J. Chem.

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. Can. J. Chem. 65, 892 (1987). The ground state properties (bond lengths, bond orders, net atomic charge distribution) of various cis and trans isomers of retinal analogs have been studied at ab initio SCF and correlated levels. The effect of protonation on the properties of the retinal Schiff base analogs has also been studied. Convergence in various properties has been observed with increasing chain length justifying the use of smaller analogs mimicking retinal. Convergence is, however, slower for the protonated retinal Schiff base analogs. The protonated retinal Schiff base analogs show an increased conjugation reflected in the bond orders, bond lengths, and in the decrease in the HOMO-LUMO gap. The nodal characteristics of the HOMO of the protonated retinal Schiff base analog also indicate a strong conjugation in the vicinity of the protonated nitrogen. Based on the results of calculations at the correlated level, the sudden polarization charge transfer mechanism is shown to be an artifact of HF-based methods used in the calculations. Utilisant des mCthodes ab initio en champ auto-cohhent et a des niveaux permettant d'Ctablir une corrtlation, on a CtudiC les propriCtCs a 1'Ctat fondamental (longueurs des liaisons, ordres des liaisons, distributions des charges atomiques nettes) des divers isomkres cis et trans d'analogues du retinal. On a aussi CtudiC l'effet de la protonation sur les propriCtts d'analogues des bases de Schiff du rCtinal. On a observk une convergence des diverses proprittts avec une augmentation de la longueur de la chaine et cette observation justifie l'utilisation d'analogues plus petits qui reproduisent les proprittCs du rCtinal; toutefois, la convergence est plus lente pour les analogues protonCs des bases de Schiff du retinal. Les analogues protones des bases de Schiff du rCtinal prksentent une plus grande conjugaison qui se rkflkte dans les ordres et les longueurs des liaisons et par une diminution de la diffkrence entre la haute occupCe et la basse vacante. Les caracttristiques nodales de la haute occupte de I'analogue proton6 de la base de Schiff du rttinal suggkrent qu'il existe une forte conjugaison au voisinage de I'azote protont. En se basant sur les rCsultats de ces calculs aux niveaux oh l'on peut ttablir une corrklation, on dCmontre que la polarisation soudaine dans le mkcanisme de transfert de charge n'a pas de signification physique et qu'elle est inhCrente aux mkthodes basCes sur HF qui sont utilistes dans les calculs.[Traduit par la revue]

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Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin

Cited by 49 publications

References 9 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

Fluorescence spectra of bacteriorhodopsin and the intermediates O and Q at room temperature

Effect of protonation on the ground state properties of retinal analogs: an ab-initio study

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