Direct Observation of the Femtosecond Excited-State cis-trans Isomerization in Bacteriorhodopsin

Mathies, R. A.; Pollard, W. Thomas; Cruz, C. H. Brito; Shank, C. V.

doi:10.1007/978-3-642-83644-2_163

Cited by 31 publications

(55 citation statements)

References 9 publications

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“…This signal is proportional to the population removed from the ground state and has a sublinear dependence on the excitation energy. Previous studies reported that the population is initially excited to the H conformation and a fluorescence Stokes shift is observed as the population moves to I 460 in Ϸ200 fs (16,23,43). This time-delay in the growth of the I 460 signal is also observed in the present experiments (see section 2.4 below).…”

Section: Resultssupporting

confidence: 88%

Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

Florean

Cardoza

White

et al. 2009

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

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A learning algorithm was used to manipulate optical pulse shapes and optimize retinal isomerization in bacteriorhodopsin, for excitation levels up to 1.8 ؋ 10 16 photons per square centimeter. Below 1/3 the maximum excitation level, the yield was not sensitive to pulse shape. Above this level the learning algorithm found that a Fourier-transform-limited (TL) pulse maximized the 13-cis population. For this optimal pulse the yield increases linearly with intensity well beyond the saturation of the first excited state. To understand these results we performed systematic searches varying the chirp and energy of the pump pulses while monitoring the isomerization yield. The results are interpreted including the influence of 1-photon and multiphoton transitions. The population dynamics in each intermediate conformation and the final branching ratio between the all-trans and 13-cis isomers are modified by changes in the pulse energy and duration.coherent control ͉ photoisomerization ͉ ultrafast science B acteriorhodopsin (bR) is a photosynthetic protein found in the purple membrane of Halobacterium salinarum and capable of conversion of solar energy into chemical energy. This energy conversion is efficient (1-3) and has several possible applications (4-12). A retinal chromophore is responsible for photon absorption. After photoexcitation retinal undergoes ultrafast isomerization from the all-trans to a 13-cis configuration, accompanied by additional changes in the conformation of bR (3,8). The initial steps of the bR photocycle (see Fig. 1) have been studied intensively (11, 13-33), but there are still unanswered questions regarding the electronic potential energy surfaces (PES) of retinal, the interaction with its surroundings in the protein, and related ultrafast vibrational coupling. A number of models have been proposed, each explaining parts of the large number of experiments (4,13,14,16,(34)(35)(36)(37)(38)(39)(40). Attempts have been made to reconcile the differences between these models (4).We aim to understand how the optical pulse shape and intensity affect the all-trans 3 13-cis yield and to explore potential pathways for producing high photoproduct yields on an ultrafast time scale. This is relevant for energy storage using bio-molecular machines (9, 32). Recently, Prokhorenko et al. showed that the isomerization yield of retinal in bR could be manipulated in a low intensity, biologically relevant regime through the use of phase and amplitude shaped optical fields (25). Modifications of as much as Ϯ20% were observed compared with unshaped pulses capable of exciting an equal number of molecules. Yet the ultimate yields remain small as photon flux was restricted to excite Ϸ0.3% of the chromophores in the excitation volume. In a different experiment, Vogt et al. used much higher intensity, shorter wavelength pump pulses to excite bR and a shaped 800-nm dump pulse to study the evolution of the molecule on the excited state PES (30). They found that the excited population is transferred most effectively back to t...

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Section: Resultssupporting

confidence: 88%

Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

Florean

Cardoza

White

et al. 2009

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

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“…First, the absorption maximum (568 nm) is red-shifted with respect to the one observed in solution (440 nm in methanol). Second, timeresolved spectroscopy reveals a dominant excited state lifetime component of 450 fs (5, 6) almost matching the 500-fs time scale for formation of the vibrationally hot primary photoproduct J (7,8). In contrast, PSBT in solution features a biexponential decay dynamics with a dominant (ca.…”

mentioning

confidence: 89%

Aborted double bicycle-pedal isomerization with hydrogen bond breaking is the primary event of bacteriorhodopsin proton pumping

Altoè

Cembran

Olivucci

et al. 2010

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

111

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Quantum mechanics/molecular mechanics calculations based on ab initio multiconfigurational second order perturbation theory are employed to construct a computer model of Bacteriorhodopsin that reproduces the observed static and transient electronic spectra, the dipole moment changes, and the energy stored in the photocycle intermediate K. The computed reaction coordinate indicates that the isomerization of the retinal chromophore occurs via a complex motion accounting for three distinct regimes: (i) production of the excited state intermediate I, (ii) evolution of I toward a conical intersection between the excited state and the ground state, and (iii) formation of K. We show that, during stage ii, a space-saving mechanism dominated by an asynchronous double bicycle-pedal deformation of the C10 ═ C11 ─ C12 ═ C13 ─ C14 ═ N moiety of the chromophore dominates the isomerization. On this same stage a N ─ H∕water hydrogen bond is weakened and initiates a breaking process that is completed during stage iii.photoisomerization | quantum mechanics/molecular mechanics (QM/MM) | retinal proteins T he light-activated proton pump bacteriorhodopsin (bR) is an Archaea receptor contained in the purple membrane of Halobacterium salinarium. As shown in Scheme 1, upon photoexcitation, the all-trans retinal chromophore (PSBT) bounded to Lys216 via a protonated Schiff base linkage is converted to the 13-cis isomer (PSB13). This event triggers a series of conformational changes that ultimately result in a proton translocation from the cytoplasmic to the extracellular domain (1).The bR protein environment affects both the spectroscopic and photochemical properties of PSBT (2-4). First, the absorption maximum (568 nm) is red-shifted with respect to the one observed in solution (440 nm in methanol). Second, timeresolved spectroscopy reveals a dominant excited state lifetime component of 450 fs (5, 6) almost matching the 500-fs time scale for formation of the vibrationally hot primary photoproduct J (7,8). In contrast, PSBT in solution features a biexponential decay dynamics with a dominant (ca. 10-fold longer) 2-ps component (9-11). Finally, although bR photoisomerizes stereoselectively (leading exclusively to PSB13) with high (ca. 67%) quantum yield (9, 12), irradiation of PSBT in solution leads to a mixture of different stereoisomers with a smaller (ca. 25%) total quantum yield (9, 13).Low-temperature spectroscopic studies provided evidence for the existence of a tiny (≤1 kcal mol −1 ) energy barrier on the excited state (S 1 ) potential energy surface of bR (14,15). Such a barrier would explain the 450-fs short-lived quasistationary state observed by Ruhman et al. (5) that is assigned to the fluorescent state I (16-18) and precedes decay to the ground state (S 0 ). Recent experiments by Léonard et al. (19) have also revealed that the photoinduced changes in the permanent dipole moment of PSBT are mirrored by the absorption of Trp86 up to the first stable (i.e., cryogenically trapped) photoproduct K (7). Relative to bR, K bears 11.7-...

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“…lt is thought that the bR photocycle consists of five (perhaps six) intermediates (Xie et al, 1987;Ames & Mathies, 1990;Varo & Lanyi, 1990 (Sharkov et al, 1985;Mathies et al, 1988;Pollard et al, 1990). Femtosecond resonance Raman spectroscopy was usgd to identify J .…”

Section: IIImentioning

confidence: 99%

Trapping the M sub 1 and M sub 2 substrates of bacteriorhodopsin for electron diffraction studies

Perkins¹

1992

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Direct Observation of the Femtosecond Excited-State cis-trans Isomerization in Bacteriorhodopsin

Cited by 31 publications

References 9 publications

Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

Aborted double bicycle-pedal isomerization with hydrogen bond breaking is the primary event of bacteriorhodopsin proton pumping

Trapping the M sub 1 and M sub 2 substrates of bacteriorhodopsin for electron diffraction studies

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