Primary picosecond molecular events in the photoreaction of the BR5.12 artificial bacteriorhodopsin pigment.

Delaney, John K.; Brack, T. L.; Atkinson, Gordon; Ottolenghi, Michael; Steinberg, G.; Sheves, Mordechai

doi:10.1073/pnas.92.6.2101

Cited by 47 publications

(74 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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: 58%

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

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...

show abstract

Section: Resultssupporting

confidence: 58%

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

show abstract

“…The specific choices were artificial pigments (I, II, and III) formed from three locked retinal analogs 1,2 (30) and 3 (31,32), in which the critical C 13 AC 14 isomerization is blocked by a 5-membered ring structure. Although pigment I shows transient absorbance and fluorescence changes on a picosecond time scale (4), all three pigments do not exhibit any of the microsecondmillisecond changes in the chromophore absorption spectrum, which characterize the photocycle of native bR (4,28,32,33). However, surprisingly, each of the three pigments was found to exhibit light-induced AFS patterns.…”

Section: Resultsmentioning

confidence: 99%

“…It is widely accepted that all light-induced protein conformational alterations in retinylidene proteins are initiated by isomerization of the retinal chromophore: 11-cis 3 trans (in visual pigments) or trans 3 13-cis (in bR). Nonetheless, alternative mechanisms have been suggested in which isomerization is not the primary trigger of the protein structural alterations (2)(3)(4)(5). One approach is based on the suggestion that a large light-induced redistribution of electronic charge in the vertically excited state causes alterations in the surrounding protein matrix and leads to the subsequent protein structural transformations (3).…”

mentioning

confidence: 99%

Microsecond atomic force sensing of protein conformational dynamics: Implications for the primary light-induced events in bacteriorhodopsin

Rousso

Khachatryan²,

Gat³

et al. 1997

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

View full text Add to dashboard Cite

In this paper a new atomic force sensing technique is presented for dynamically probing conformational changes in proteins. The method is applied to the light-induced changes in the membrane-bound proton pump bacteriorhodopsin (bR). The microsecond time-resolution of the method, as presently implemented, covers many of the intermediates of the bR photocycle which is well characterized by spectroscopical methods. In addition to the native pigment, we have studied bR proteins substituted with chemically modified retinal chromophores. These synthetic chromophores were designed to restrict their ability to isomerize, while maintaining the basic characteristic of a large lightinduced charge redistribution in the vertically excited Franck--Condon state. An analysis of the atomic force sensing signals lead us to conclude that protein conformational changes in bR can be initiated as a result of a light-triggered redistribution of electronic charge in the retinal chromophore, even when isomerization cannot take place. Although the coupling mechanism of such changes to the light-induced proton pump is still not established, our data question the current working hypothesis which attributes all primary events in retinal proteins to an initial transNcis isomerization.

show abstract

“…Some examples are as follows: (i) replacement of the vinyl bond by either a single or a triple bond, (ii) isotopically labeled derivatives, and (iii) chromophore analogues in which the vinyl bond is locked through a covalent bridge (compare Ref. 28).…”

Section: Resultsmentioning

confidence: 99%

Spectral Tuning, Fluorescence, and Photoactivity in Hybrids of Photoactive Yellow Protein, Reconstituted with Native or Modified Chromophores

Kroon¹,

Hoff²,

Fennema

et al. 1996

Journal of Biological Chemistry

100

133

View full text Add to dashboard Cite

Photoactive yellow proteins (PYPs) constitute a new class of eubacterial photoreceptors, containing a deprotonated thiol ester-linked 4-hydroxycinnamic acid chromophore. Interactions with the protein dramatically change the (photo)chemical properties of this cofactor. Here we describe the reconstitution of apoPYP with anhydrides of various chromophore analogues. The resulting hybrid PYPs, their acid-denatured states, and corresponding model compounds were characterized with respect to their absorption spectrum, pK for chromophore deprotonation, fluorescence quantum yield, and Stokes shift. Three factors contributing to the tuning of the absorption of the hybrid PYPs were quantified: (i) thiol ester bond formation, (ii) chromophore deprotonation, and (iii) specific chromophore-protein interactions. Analogues lacking the 4-hydroxy substituent lack both contributions (chromophore deprotonation and specific chromophore-protein interactions), confirming the importance of this substituent in optical tuning of PYP. Hydroxy and methoxy substituents in the 3-and/or 5-position do not disrupt strong interactions with the protein but increase their pK for protonation and the fluorescence quantum yield. Both deprotonation and binding to apoPYP strongly decrease the Stokes shift of chromophore fluorescence. Therefore, coupling of the chromophore to the apoprotein not only reduces the energy gap between its ground and excited state but also the extent of reorganization between these two states. Two of the PYP hybrids show photoactivity comparable with native PYP, although with retarded recovery of the initial state.

show abstract

Primary picosecond molecular events in the photoreaction of the BR5.12 artificial bacteriorhodopsin pigment.

Cited by 47 publications

References 29 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

Microsecond atomic force sensing of protein conformational dynamics: Implications for the primary light-induced events in bacteriorhodopsin

Spectral Tuning, Fluorescence, and Photoactivity in Hybrids of Photoactive Yellow Protein, Reconstituted with Native or Modified Chromophores

Contact Info

Product

Resources

About