Protons @ interfaces: Implications for biological energy conversion

Mulkidjanian, Armen Y.; Heberle, Joachim; Cherepanov, Dmitry A.

doi:10.1016/j.bbabio.2006.02.015

Cited by 183 publications

(209 citation statements)

References 197 publications

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“…Furthermore, the data indicate that the mode of protonation of a membrane-associated proton acceptor can switch from a membrane-promoted to a direct exchange with the bulk solution. This protonation mechanism is likely to be a general feature also for a wide range of membrane-associated proton transporters, such as cytochrome c oxidase, photosynthetic reaction centers, and bacteriorhodopsin (9,15,30) in living cells.…”

Section: Discussionmentioning

confidence: 92%

“…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)(2)(3)(4)(5)(6)(7)(8). 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).…”

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confidence: 99%

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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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Section: Discussionmentioning

confidence: 92%

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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“…Biological interfaces are however more complex, due to their strong and local dependence on the surrounding pH, and the conformational flexibility of the molecules. Correlated ionic networks are however likely to play key roles in charge transfer 12,38 and membrane shaping 58 , and both experiments and simulations are already underway to examine these possibilities.…”

Section: Discussionmentioning

confidence: 99%

“…The latter is chemically different than mica and, although only weakly charged, provides an appropriate hydration landscape that allows for the formation of ionic structures stable enough to be observed by AFM. The generality of the effect suggests that it could play an important role in wide range of systems, for example, in controlling and enhancing charge transport at interfaces 12,38 , in influencing crystal growth 17 or the stability of colloidal solutions and emulsions 18 . In addition, this effect could also be exploited in the design and self-assembly of nanomaterials 39 and used to template nanostructures 16 .…”

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confidence: 99%

Water-induced correlation between single ions imaged at the solid–liquid interface

2014

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When immersed into water, most solids develop a surface charge, which is neutralized by an accumulation of dissolved counterions at the interface. Although the density distribution of counterions perpendicular to the interface obeys well-established theories, little is known about counterions' lateral organization at the surface of the solid. Here we show, by using atomic force microscopy and computer simulations, that single hydrated metal ions can spontaneously form ordered structures at the surface of homogeneous solids in aqueous solutions. The structures are laterally stabilized only by water molecules with no need for specific interactions between the surface and the ions. The mechanism, studied here for several systems, is controlled by the hydration landscape of both the surface and the adsorbed ions. The existence of discrete ion domains could play an important role in interfacial phenomena such as charge transfer, crystal growth, nanoscale self-assembly and colloidal stability.

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“…More recent experimental and theoretical studies indicate that rapid proton diffusion along surfaces of biological membranes plays a functional role (for review, see refs. [4][5][6][7].…”

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confidence: 99%

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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Protons @ interfaces: Implications for biological energy conversion

Cited by 183 publications

References 197 publications

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

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

Water-induced correlation between single ions imaged at the solid–liquid interface

Functional interactions between membrane-bound transporters and membranes

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