D38 Is an Essential Part of the Proton Translocation Pathway in Bacteriorhodopsin

Riesle, Jens; Oesterhelt, Dieter; Dencher, Norbert A.; Heberle, Joachim

doi:10.1021/bi9600456

Cited by 113 publications

(107 citation statements)

References 51 publications

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“…Furthermore, we showed recently that incorporation of CytcO into a membrane results in acceleration of the protonation rate of a surface-exposed pH-sensitive fluorescent dye at the n side of the membrane (49). Also data from earlier studies show that proton migration along proteinmembrane surfaces may be faster than proton exchange between surface residues and the bulk solution (50), which involves specific surface residues (51,52).…”

Section: Discussionmentioning

confidence: 94%

Functional interactions between membrane-bound transporters and membranes

Öjemyr

Lee

Gennis

et al. 2010

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

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One key role of many cellular membranes is to hold a transmembrane electrochemical ion gradient that stores free energy, which is used, for example, to generate ATP or to drive transmembrane transport processes. In mitochondria and many bacteria, the gradient is maintained by proton-transport proteins that are part of the respiratory (electron-transport) chain. Even though our understanding of the structure and function of these proteins has increased significantly, very little is known about the specific role of functional protein-membrane and membrane-mediated proteinprotein interactions. Here, we have investigated the effect of membrane incorporation on proton-transfer reactions within the membrane-bound proton pump cytochrome c oxidase. The results show that the membrane acts to accelerate proton transfer into the enzyme's catalytic site and indicate that the intramolecular proton pathway is wired via specific amino acid residues to the twodimensional space defined by the membrane surface. We conclude that the membrane not only acts as a passive barrier insulating the interior of the cell from the exterior solution, but also as a component of the energy-conversion machinery.cytochrome aa3 | electron transfer | energy transduction | membrane protein | respiration

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Section: Discussionmentioning

confidence: 94%

Functional interactions between membrane-bound transporters and membranes

Öjemyr

Lee

Gennis

et al. 2010

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

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“…On the "macroscopic" level, the ability of surface buffers to retard the propagation of a proton pulse was addressed both experimentally [32,33] and theoretically [30,31,34,35]. On the "microscopic" level, it has been shown that the replacement of particu lar amino acid residues at the n surface of BR membranes affected the enzyme kinetics [36]. These data indicated the contribution of the surface exposed amino acids in the efficient collection/trapping of protons (further evidence of such involvement can be found in review [37]).…”

Section: Interfacial Potential Barrier: Propertiesmentioning

confidence: 99%

Proton transfer dynamics at membrane/water interface and mechanism of biological energy conversion

Mulkidjanian

Cherepanov

Heberle³

et al. 2005

Biochemistry (Moscow)

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A retrospective account of studies on proton transfer dynamics at the membrane surface might be an appropri ate contribution to this special issue in honor of Vladimir Skulachev, who has published seminal works in this field. Below we focus on the mechanisms of proton transfer both across and along the membrane/water interface as inferred from pulse experiments with light triggered enzymes ejecting or capturing protons at the membrane surface. We consider these data in their relation to the mechanism of energy conversion in the living cell.It is widely accepted that the transmembrane differ ence in the electrochemical potential of hydrogen ions (∆μ Н +) is a major intermediate in the cellular energy transduction [1 3]. ∆μ Н + is generated by redox or light driven proton pumps. It is utilized by the energy consum ing enzymes, the ATP synthase in the first line and by secondary transporters in the second. In some bacteria, ∆μ Н + is functionally replaced/complemented by the sodi um potential (∆μ Na +) (see [4] for a review). Still the majority of bacteria, and, importantly, the plant chloro plasts and the animal mitochondria use only ∆μ Н +. Mitchell coined the term protonmotive force (pmf) [2]:where ∆ψ is the transmembrane electrical potential dif ference, and ∆pH is the pH difference between the two sides of the membrane, namely the positively charged side p and the negatively charged side n. ∆pH was initially conceived by Mitchell as the difference existing between the two bulk phases separated by the membrane [2]. Williams, however, challenged this notion by arguing that in bacteria the p phase corresponds to the infinitely extended external space. If protons are extruded into this "Pacific Ocean", they would be diluted and the entropic component of the pmf would be lost [5]. This argument is Biochemistry (Moscow), Vol. 70, No. 2, 2005, pp. 251 256. Translated from Biokhimiya, Vol. 70, No. 2, 2005, pp. 308 314. Original Russian Text Copyright © 2005 Abstract-Proton transfer between water and the interior of membrane proteins plays a key role in bioenergetics. Here we sur vey the mechanism of this transfer as inferred from experiments with flash triggered enzymes capturing or ejecting protons at the membrane surface. These experiments have revealed that proton exchange between the membrane surface and the bulk water phase proceeds at ≥1 msec because of a kinetic barrier for electrically charged species. From the data analysis, the bar rier height for protons could be estimated as about 0.12 eV, i.e., high enough to account for the observed retardation in pro ton exchange. Due to this retardation, the proton activity at the membrane surface might deviate, under steady turnover of proton pumps, from that measured in the adjoining water phase, so that the driving force for ATP synthesis might be higher than inferred from the bulk to bulk measurements. This is particularly relevant for alkaliphilic bacteria. The proton diffusion along the membrane surface, on the other hand, is unconstrained and fast, occurring b...

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“…Studies on some specific membrane-bound proton pumps, for example cytochrome c oxidase or bacteriorhodopsin (9)(10)(11)(12), have revealed higher than diffusion-limited rates of proton uptake (9,(13)(14)(15). It has been hypothesized that these proteins have a surface proton-collecting antenna, consisting of negative and buffering groups, aiding the proton uptake (12,16,17). Theoretical studies also indicate that the membrane itself can contribute to this proton uptake (18)(19)(20).…”

mentioning

confidence: 99%

Surface-coupled proton exchange of a membrane-bound proton acceptor

Sandén

Salomonsson

Brzezinski

et al. 2010

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

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Proton-transfer reactions across and at the surface of biological membranes are central for maintaining the transmembrane proton electrochemical gradients involved in cellular energy conversion. In this study, fluorescence correlation spectroscopy was used to measure the local protonation and deprotonation rates of single pHsensitive fluorophores conjugated to liposome membranes, and the dependence of these rates on lipid composition and ion concentration. Measurements of proton exchange rates over a wide proton concentration range, using two different pH-sensitive fluorophores with different pK a s, revealed two distinct proton exchange regimes. At high pH (>8), proton association increases rapidly with increasing proton concentrations, presumably because the whole membrane acts as a proton-collecting antenna for the fluorophore. In contrast, at low pH (<7), the increase in the proton association rate is slower and comparable to that of direct protonation of the fluorophore from the bulk solution. In the latter case, the proton exchange rates of the two fluorophores are indistinguishable, indicating that their protonation rates are determined by the local membrane environment. Measurements on membranes of different surface charge and at different ion concentrations made it possible to determine surface potentials, as well as the distance between the surface and the fluorophore. The results from this study define the conditions under which biological membranes can act as proton-collecting antennae and provide fundamental information on the relation between the membrane surface charge density and the local proton exchange kinetics.biomembrane | diffusion | electrostatic potential | fluorescence correlation spectroscopy (FCS) | proton transfer E nergy conversion in living cells typically involves proton translocation across a membrane, via proton transporters. These transporters maintain a proton electrochemical gradient utilizing free energy provided, for example by electron transfer or light. The free energy stored in this gradient is used, e.g., for transmembrane transport, motility, or synthesis of ATP by the ATP synthase. Results from a range of studies indicate that the membrane plays an important role in these processes, in addition to serving as a barrier. The membrane surface may also provide a proton link between the various membrane-embedded proteins, where the mere two-dimensional confinement of the reactants can also play a role. Enhancement of reaction rates between solute molecules and their target molecules on the surface and in the vicinity of biological membrane interfaces (e.g. ligand binding to membrane proteins) has been demonstrated in several studies and explained in terms of initial nonspecific binding of the solute molecules to the membrane followed by diffusion along the surface to their target molecules (1-8). Studies on some specific membrane-bound proton pumps, for example cytochrome c oxidase or bacteriorhodopsin (9-12), have revealed higher than diffusion-limited rates of proton upta...

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D38 Is an Essential Part of the Proton Translocation Pathway in Bacteriorhodopsin

Cited by 113 publications

References 51 publications

Functional interactions between membrane-bound transporters and membranes

Functional interactions between membrane-bound transporters and membranes

Proton transfer dynamics at membrane/water interface and mechanism of biological energy conversion

Surface-coupled proton exchange of a membrane-bound proton acceptor

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