Dimeric-like kinetic cooperativity of the bacteriorhodopsin molecules in purple membranes

Tokaji, Zsolt

doi:10.1016/s0006-3495(93)81165-2

Cited by 30 publications

(31 citation statements)

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“…We concluded that this altered decay kinetics is caused by the interaction between bR molecules that are excited together not within a trimer but within a 'trefoil'. Earlier works have also reported that the spectroscopically measured kinetics of the bR photocycle is altered depending on light intensity, and attributed the observed cooperative effects to neighboring effects within trimers (Rehorek et al, 1979;Tokaji, 1993) or general crowding effects in the lattice (e.g., Varo et al, 1996). However, the cooperative effects observed in these ensemble-averaged spectroscopic measurements are not as distinct as those observed by HS-AFM, which is due likely to the bipolar nature of the cooperativity.…”

Section: Analysis Of Reaction Kinetics and Its Comparison Between D96mentioning

confidence: 95%

Role of trimer–trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy

Yamashita

Inoue

Shibata

et al. 2013

Journal of Structural Biology

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Bacteriorhodopsin (bR) trimers form a two-dimensional hexagonal lattice in the purple membrane of Halobacterium salinarum. However, the physiological significance of forming the lattice has long been elusive. Here, we study this issue by comparing properties of assembled and non-assembled bR trimers using directed mutagenesis, high-speed atomic force microscopy (HS-AFM), optical spectroscopy, and a proton pumping assay. First, we show that the bonds formed between W12 and F135 amino acid residues are responsible for trimer-trimer association that leads to lattice assembly; the lattice is completely disrupted in both W12I and F135I mutants. HS-AFM imaging reveals that both crystallized D96N and non-crystallized D96N/W12I mutants undergo a large conformational change (i.e., outward E-F loop displacement) upon light-activation. However, lattice disruption significantly reduces the rate of conformational change under continuous light illumination. Nevertheless, the quantum yield of M-state formation, measured by low-temperature UV-visible spectroscopy, and proton pumping efficiency are unaffected by lattice disruption. From these results, we conclude that trimer-trimer association plays essential roles in providing bound retinal with an appropriate environment to maintain its full photo-reactivity and in maintaining the natural photo-reaction pathway.

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Section: Analysis Of Reaction Kinetics and Its Comparison Between D96mentioning

confidence: 95%

Role of trimer–trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy

Yamashita

Inoue

Shibata

et al. 2013

Journal of Structural Biology

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“…The effect of actinic light has either been ignored (e.g. Lanyi et al, 1992), explained by invocation of photocooperativity (Ohno et al, 1981;Dancshazy et al, 1988;Tokaji, 1993), or by heterogeneity of BR populations (e.g. Hendler et al, 1994).…”

Section: Discussionmentioning

confidence: 99%

“…This shows that it is possible to explain the data purely on cooperativity, but does not establish that this is the case. We also examined direct evidence which was interpreted as a strong experimental case for cooperativity (Tokaji andDancshazy, 1991, 1992).…”

Section: Discussionmentioning

confidence: 99%

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The Ability of Actinic Light to Modify the Bacteriorhodopsin Photocycle

Shrager

Hendler

Bose

1995

European Journal of Biochemistry

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The focus of this paper is on the established observation that the bacteriorhodopsin (BR) photocycle responds to the level of actinic light by altering the proportions of two forms of the M intermediate. The first form of M, called M-fast or M, decays to the 0 intermediate. In contrast, the second form of M, called M-slow or M,, decays directly to the ground state, and its decay rate is slower than that of MF Any proposed scheme for the BR photocycle must account for this light-dependent phenomenon. Several papers have attempted to explain the observation on the basis of photocooperativity, or on the basis of heterogeneous populations. In this paper, we test previously proposed cooperative models with experimental data, and find those models to be inadequate. We show that two new models, one purely cooperative, the other purely heterogeneous, can both fit the data, hence such modelling will not resolve the mechanism. Taking into account the demonstration of heterogeneity, the trimer structure of BR, and certain experimental evidence in favor of cooperativity, it appears likely that both heterogeneity and cooperativity are involved in the adaptation of the BR photocycle to different levels of actinic light.Keywords. Bacteriorhodopsin ; light intensity ; photocycle regulation ; mathematical models ; kinetics ; M-intermediates.Bacteriorhodopsin (BR) is a transmembrane protein that acts as a light-driven pump in the purple membrane of halobacteria Stoeckenius, 1971, 1973). Upon exposure to light, BR cycles through several intermediates which are currently labeled K, L, M, N and 0, with possible subspecies and branchings. Slifkin and Caplan (1975) demonstrated that (at least) two species of M intermediate were present with different lifetimes. Since then, the presence of two distinct species of M has been repeatedly confirmed (see Hendler et al., 1994, for references). A very important finding was made by Ohno et al. (1981), namely that the ratio of fast and slow forms of M (i.e. M, and Ms), was modulated by the intensity of the actinic flash used to initiate the photocycle, producing changes in the shapes of the kinetic curves. At low flash intensities, the MF species was predominant, but with increasing light intensities, the fraction of MR i.e. Mp/(MF + Ms), decreased to <0.5. This finding has also been repeatedly confirmed (see Hendler et al., 1994, for references). More recently, it has been shown that M, decays directly to the 0 intermediate, whereas M, decays directly to BR (Eisfeld et al., 1993;Hendler et al., 1994). At present, there are many different views on the nature of the photocycle, and a general consensus is lacking. An important criterion for narrowing the field of possibly correct photocycle models is the ability of those models to explain (i.e. fit) experimental kinetic data taken over a considerable range of actinic light intensities. It is also important for these models to account for the various decay pathways for the M, and M, intermediates. In this context, we will examine a variety of c...

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“…A recently rediscovered effect, the actinic light density dependence of the photocycle kinetics [2] and the origin of it, a photocooperativity among the neighboring BR molecules in the purple membrane [3], will probably affect the solution of this latter problem: in the case of a sample containing the mixture of the photocycling molecules with and without photocycling neighbors, the appearance of at least two parallel pathways seems to be natural. One pathway corresponds to the unaltered photocycle and the other to the altered one.…”

Section: Introductionmentioning

confidence: 99%

Cooperativity‐regulated parallel pathways of the bacteriorhodopsin photocycle

Tokaji

1995

FEBS Letters

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Dimeric-like kinetic cooperativity of the bacteriorhodopsin molecules in purple membranes

Cited by 30 publications

References 13 publications

Role of trimer–trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy

Role of trimer–trimer interaction of bacteriorhodopsin studied by optical spectroscopy and high-speed atomic force microscopy

The Ability of Actinic Light to Modify the Bacteriorhodopsin Photocycle

Cooperativity‐regulated parallel pathways of the bacteriorhodopsin photocycle

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