Evidence for parallel photocycles and implications for the proton pump in bacteriorhodopsin

Eisfeld, W.; Althaus, T.; Stockburger, Manfred

doi:10.1016/0301-4622(95)00021-o

Cited by 12 publications

(6 citation statements)

References 8 publications

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“…Two primary models have been put forward to explain the M kinetics. The first is one of parallel photocycles, starting with two ground state bR species, which go through their own photocycle kinetics but have the same spectral intermediates (Balashov et al, 1991;Eisfeld et al, 1995;Hendler et al, 2001). The second model assumes that there is a transition between two M states that is spectrally silent in the visible region Lanyi, 1990, 1991b;Perkins et al, 1992;Oka et al, 2002).…”

Section: Resultsmentioning

confidence: 99%

Proton Transfer Reactions in Native and Deionized Bacteriorhodopsin upon Delipidation and Monomerization

Heyes

El‐Sayed

2003

Biophysical Journal

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We have investigated the role of the native lipids on bacteriorhodopsin (bR) proton transfer and their connection with the cation-binding role. We observe that both the efficiency of M formation and the kinetics of M rise and decay depend on the lipids and lattice but, as the lipids are removed, the cation binding is a much less important factor for the proton pumping function. Upon 75% delipidation using 3-[(cholamidopropyl)dimethylammonio]-propanesulfonate (CHAPS), the M formation and decay kinetics are much slower than the native, and the efficiency of M formation is approximately 30%-40% that of the native. Upon monomerization of bR by Trition X-100, the efficiency of M recovers close to that of the native (depending on pH), M formation is approximately 10 times faster, and M decay kinetics are comparable to native at pH 7. The same results on the M intermediate are observed if deionized blue bR (deI bbR) is treated with these detergents (with or without pH buffers present), even though deionized blue bR containing all the lipids has no photocycle. This suggests that the cation(s) has a role in native bR that is different than in delipidated or monomerized bR, even so far as to suggest that the cation(s) becomes unimportant to the function as the lipids are removed.

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Section: Resultsmentioning

confidence: 99%

Proton Transfer Reactions in Native and Deionized Bacteriorhodopsin upon Delipidation and Monomerization

Heyes

El‐Sayed

2003

Biophysical Journal

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“…This assumption has also been shown to be invalid. 2,14 Nevertheless, Morgan et al concluded that there is a pH dependence of a very small component, centered near 1885 cm À1 , that is part of a larger pH-invariant negative continuum absorbance band extending over most of the spectral region above 1600 cm À1 . They attributed the small component centered near 1885 cm À1 to a protonated water cation serving as the PRG.…”

Section: Discussionmentioning

confidence: 99%

“…2, 3, 9–16 Hendler and coworkers have pointed out many experimental observations that can not be explained by a homogeneous sequential linear cycle. 2, 10, 13, 14 Most important, when using short (~10 ns) laser pulses for actinic excitation of bR, the yield of any particular photointermediate produced from a homogeneous ground state is expected to rise linearly at low intensities, and then to exhibit a saturation curve with an exponential behavior. That is, the photoproduct yield as a function of incident pulse energy E (in photons per cm 2 ) should be in proportion to [1- exp(- kE )], where k is a constant dependent on the bR extinction coefficient and quantum yield.…”

Section: Methodsmentioning

confidence: 99%

Infrared and Visible Absolute and Difference Spectra of Bacteriorhodopsin Photocycle Intermediates

Hendler

Meuse

Braiman³

et al. 2011

Appl Spectrosc

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We have used new kinetic fitting procedures to obtain IR absolute spectra for intermediates of the main bacteriorhodopsin (bR) photocycle(s). The linear algebra-based procedures of Hendler et al. (2001) J. Phys. Chem. B, 105, 3319–3228, for obtaining clean absolute visible spectra of bR photocycle intermediates, were adapted for use with IR data. This led to isolation, for the first time, of corresponding clean absolute IR spectra, including the separation of the M intermediate into its MF and MS components from parallel photocycles. This in turn permitted the computation of clean IR difference spectra between pairs of successive intermediates, allowing for the most rigorous analysis to date of changes occurring at each step of the photocycle. The statistical accuracy of the spectral calculation methods allows us to identify, with great confidence, new spectral features. One of these is a very strong differential IR band at 1650 cm−1 for the L intermediate at room temperature that is not present in analogous L spectra measured at cryogenic temperatures. This band, in one of the noisiest spectral regions, has not been identified in any previous time-resolved IR papers, although retrospectively it is apparent as one of the strongest L absorbance changes in their raw data, considered collectively. Additionally, our results are most consistent with Arg82 as the primary proton-release group (PRG), rather than a protonated water cluster or H-bonded grouping of carboxylic residues. Notably, the Arg82 deprotonation occurs exclusively in the MF pathway of the parallel cycles model of the photocycle.

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“…In native bR, two primary models have been presented to account for the biexponential rise. The first model is of that of parallel photocycles: that there are two different ground state bR species, each going through their own photocycle with the same spectral intermediates (39)(40)(41). The other model assumes that there is only one photocycle but that there is a transition between two M states, M 1 and M 2 , that is spectrally silent in the visible region (35,(42)(43)(44).…”

Section: Resultsmentioning

confidence: 99%

The Protonation-Deprotonation Kinetics of the Protonated Schiff Base in Bicelle Bacteriorhodopsin Crystals

Sanii

Schill

Moran

et al. 2005

Biophysical Journal

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In the recently published x-ray crystal structure of the "bicelle" bacteriorhodopsin (bbR) crystal, the protein has quite a different structure from the native and the in cubo bacteriorhodopsin (cbR) crystal. Instead of packing in parallel trimers as do the native membrane and the cbR crystals, in the bbR crystal the protein packs as antiparallel monomers. To date, no functional studies have been performed, to our knowledge, to investigate if the photocycle is observed in this novel protein packing structure. In this study, both Raman and time-resolved transient absorption spectroscopy are used to both confirm the presence of the photocycle and investigate the deprotonation-reprotonation kinetics of the Schiff base proton in the bbR crystal. The observed rates of deprotonation and reprotonation processes of its Schiff base have been compared to those observed for native bR under the same conditions. Unlike the previously observed similarity of the rates of these processes for cbR crystals and those for native bacteriorhodopsin (bR), in bbR crystals the rate of deprotonation has increased by 300%, and the rate of reprotonation has decreased by nearly 700%. These results are discussed in light of the changes observed when native bR is delipidated or monomerized by detergents. Both the change of the hydrophobicity of the environment around the protonated Schiff base and Asp85 and Asp96 (which could change the pKa values of proton donor-acceptor pairs) and the water structure in the bbR crystal are offered as possible explanations for the different observations.

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Evidence for parallel photocycles and implications for the proton pump in bacteriorhodopsin

Cited by 12 publications

References 8 publications

Proton Transfer Reactions in Native and Deionized Bacteriorhodopsin upon Delipidation and Monomerization

Proton Transfer Reactions in Native and Deionized Bacteriorhodopsin upon Delipidation and Monomerization

Infrared and Visible Absolute and Difference Spectra of Bacteriorhodopsin Photocycle Intermediates

The Protonation-Deprotonation Kinetics of the Protonated Schiff Base in Bicelle Bacteriorhodopsin Crystals

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