A unifying concept for ion translocation by retinal proteins

Oesterhelt, Dieter; Tittor, Jörg; Bamberg, Ernst

doi:10.1007/bf00762676

Cited by 236 publications

(209 citation statements)

References 79 publications

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“…BR and HR function as light-driven proton and chloride pumps (6,7), respectively, whereas SRI and SRII form complexes with their transducers HtrI and HtrII, respectively, and mediate phototaxis responses (8,9). SRI absorbs orange-red light and, in complex with HtrI, mediates attractant responses to orangered light as well as repellent responses to near-UV light, which is absorbed by the photoproduct produced by the first orangered photon.…”

mentioning

confidence: 99%

Opposite Displacement of Helix F in Attractant and Repellent Signaling by Sensory Rhodopsin-Htr Complexes

Sasaki¹,

Tsai

Spudich³

2011

Journal of Biological Chemistry

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Two forms of the phototaxis receptor sensory rhodopsin I distinguished by differences in its photoactive site have been shown to be directly correlated with attractant and repellent signaling by the dual-signaling protein. In prior studies, differences in the photoactive site defined the two forms, namely the direction of light-induced proton transfer from the chromophore and the pK a of an Asp counterion to the protonated chromophore. Here, we show by both in vivo and in vitro measurements that the two forms are distinct protein conformers with structural similarities to two conformers seen in the light-driven proton transport cycle of the related protein bacteriorhodopsin. Measurements of spontaneous cell motility reversal frequencies, an in vivo measure of histidine kinase activity in the phototaxis system, indicate that the two forms are a photointerconvertible pair, with one conformer activating and the other inhibiting the kinase. Protein conformational changes in these photoconversions monitored by site-directed spin labeling show that opposite structural changes in helix F, distant from the photoactive site, correspond to the opposite phototaxis signals. The results provide the first direct evidence that displacements of helix F are directly correlated with signaling and impact our understanding of the sensory rhodopsin I signaling mechanism and the evolution of diverse functionality in this protein family.

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mentioning

confidence: 99%

Opposite Displacement of Helix F in Attractant and Repellent Signaling by Sensory Rhodopsin-Htr Complexes

Sasaki¹,

Tsai

Spudich³

2011

Journal of Biological Chemistry

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“…[1][2][3][4]. These internal proton transfers are accompanied by proton release and uptake at the respective surfaces, completing the net transfer of a proton from one membrane side to the other.…”

mentioning

confidence: 99%

Determination of the transiently lowered pKa of the retinal Schiff base during the photocycle of bacteriorhodopsin.

Brown

Lanyi

1996

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

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Reprotonation of the transiently deproto- 10-fold as the pH was lowered 1 unit, consistent with HN3 being the active species (9). This was in accord with the suggestion that the very slow rate of Schiff base protonation in D96N was not caused by a defect in proton conduction between the cytoplasmic surface and the protein interior, because the pH dependence of the rate implicated the capture of the proton at the surface as the rate-limiting step. Presumably, the hydrophobic HN3 is taken up more effectively than H+. Since in the high pH range the accelerated reprotonation occurred at a much lower molar concentration of HN3 than bacteriorhodopsin (9), such a mechanism would be accomplished only if azide shuttled rapidly, and many times in a single photocycle, between the interior of the protein and the bulk solution, much like an uncoupler of oxidative phosphorylation shuttles between the two sides of the membrane and carries protons. This is an intriguing possibility because HN3 and N3 would both have to traverse part or all of the pathway of the proton through the 10-A-long channel that leads from the cytoplasmic surface to the Schiff base (17). If correct, the details of this mechanism would affect current ideas on how protons can be transferred over long distances inside proteins.Recently, a different mechanism was suggested for the effect of azide on Schiff base protonation (18). Infrared difference spectra detected azide binding to bacteriorhodopsin through the fact that the vibrational band of N3 was depleted and the band of protonated azide appeared. Thus, azide became transiently protonated rather than deprotonated during the photocycle. The details of the formation of HN3 are not entirely clear; it seems to take place well before the reprotonation of the Schiff base, occurs also in the photocycle of the D85N mutant where little of the M state is formed and in the wild type where azide is very ineffective, and could be observed only at pH below 7.5 even though the effect of azide on M decay persists up to much higher pH. Nevertheless, the finding of protonation is contrary to what is expected if azide is the proton donor. Furthermore, single amino acid replacements in the extracellular region of the protein shifted the frequency of the band of the bound N3, suggesting that azide binds not in the cytoplasmic but in the extracellular domain. It was proposed, therefore, that azide does not act as a proton carrier. Instead, N3 binds near Asp-85 and affects the movement of protons by reorganizing a long-range hydrogenbonded chain that extends across the protein from this region to the cytoplasmic surface, disrupted in the D96N mutant by the replacement of Asp-96. Although the binding of the azide was detected through its protonation, it was suggested that the protonation of N3 is not necessarily part of this mechanism.We recognized that independent of these alternative mechanisms, the D96N mutant offers the possibility to determine the elusive pKa of the retinal Schiff base during the photocycle.The Sc...

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“…As also reported in the [13], the transmembrane protein BR is one of the simplest known active membrane transport system [20][21][22][23][24] with a well-established structure. Trimers of BR proteins are placed in a hexagonal two-dimension lattice within the purple membrane, thereby forming a real crystalline structure similar to a photonic crystal or to a "natural optical chiral metamaterial," belonging to the point group symmetry P3.…”

Section: Bacteriorhodopsin Filmmentioning

confidence: 62%

Detection of second-order nonlinear optical magnetization by mapping normalized Stokes parameters

et al. 2013

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A measurable magnetic (nonlocal) contribution to the second harmonic generation (SHG) of nonmagnetic materials is an intriguing issue related to chiral materials, such as biomolecules. Here we report the detection of an intensity-dependent optically induced magnetization of a chiral bacteriorhodopsin film under femtosecond pulse excitation (830 nm) and far from the material's resonance. The analysis of the pump intensity-dependent noncollinear SHG signal, by means of the polarization map of normalized Stokes parameters, allows one to improve the detection of the nonlinear optical magnetization M2ω contribution to the SHG signal.

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A unifying concept for ion translocation by retinal proteins

Cited by 236 publications

References 79 publications

Opposite Displacement of Helix F in Attractant and Repellent Signaling by Sensory Rhodopsin-Htr Complexes

Opposite Displacement of Helix F in Attractant and Repellent Signaling by Sensory Rhodopsin-Htr Complexes

Determination of the transiently lowered pKa of the retinal Schiff base during the photocycle of bacteriorhodopsin.

Detection of second-order nonlinear optical magnetization by mapping normalized Stokes parameters

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