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Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers

Lipid membrane surfaces can act as proton-collecting antennae, accelerating proton uptake by membrane-bound proton transporters. We investigated this phenomenon in lipid nanodiscs (NDs) at equilibrium on a local scale, analyzing fluorescence fluctuations of individual pH-sensitive fluorophores at th...

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Autores principales: Xu, Lei, Öjemyr, Linda Näsvik, Bergstrand, Jan, Brzezinski, Peter, Widengren, Jerker
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Biophysical Society 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4939474/
https://www.ncbi.nlm.nih.gov/pubmed/27166807
http://dx.doi.org/10.1016/j.bpj.2016.03.035
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author Xu, Lei
Öjemyr, Linda Näsvik
Bergstrand, Jan
Brzezinski, Peter
Widengren, Jerker
author_facet Xu, Lei
Öjemyr, Linda Näsvik
Bergstrand, Jan
Brzezinski, Peter
Widengren, Jerker
author_sort Xu, Lei
collection PubMed
description Lipid membrane surfaces can act as proton-collecting antennae, accelerating proton uptake by membrane-bound proton transporters. We investigated this phenomenon in lipid nanodiscs (NDs) at equilibrium on a local scale, analyzing fluorescence fluctuations of individual pH-sensitive fluorophores at the membrane surface by fluorescence correlation spectroscopy (FCS). The protonation rate of the fluorophores was ∼100-fold higher when located at 9- and 12-nm diameter NDs, compared to when in solution, indicating that the proton-collecting antenna effect is maximal already for a membrane area of ∼60 nm(2). Fluorophore-labeled cytochrome c oxidase displayed a similar increase when reconstituted in 12 nm NDs, but not in 9 nm NDs, i.e., an acceleration of the protonation rate at the surface of cytochrome c oxidase is found when the lipid area surrounding the protein is larger than 80 nm(2), but not when below 30 nm(2). We also investigated the effect of external buffers on the fluorophore proton exchange rates at the ND membrane-water interfaces. With increasing buffer concentrations, the proton exchange rates were found to first decrease and then, at millimolar buffer concentrations, to increase. Monte Carlo simulations, based on a simple kinetic model of the proton exchange at the membrane-water interface, and using rate parameter values determined in our FCS experiments, could reconstruct both the observed membrane-size and the external buffer dependence. The FCS data in combination with the simulations indicate that the local proton diffusion coefficient along a membrane is ∼100 times slower than that observed over submillimeter distances by proton-pulse experiments (D(s) ∼ 10(−5)cm(2)/s), and support recent theoretical studies showing that proton diffusion along membrane surfaces is time- and length-scale dependent.
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spelling pubmed-49394742017-05-10 Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers Xu, Lei Öjemyr, Linda Näsvik Bergstrand, Jan Brzezinski, Peter Widengren, Jerker Biophys J Membranes Lipid membrane surfaces can act as proton-collecting antennae, accelerating proton uptake by membrane-bound proton transporters. We investigated this phenomenon in lipid nanodiscs (NDs) at equilibrium on a local scale, analyzing fluorescence fluctuations of individual pH-sensitive fluorophores at the membrane surface by fluorescence correlation spectroscopy (FCS). The protonation rate of the fluorophores was ∼100-fold higher when located at 9- and 12-nm diameter NDs, compared to when in solution, indicating that the proton-collecting antenna effect is maximal already for a membrane area of ∼60 nm(2). Fluorophore-labeled cytochrome c oxidase displayed a similar increase when reconstituted in 12 nm NDs, but not in 9 nm NDs, i.e., an acceleration of the protonation rate at the surface of cytochrome c oxidase is found when the lipid area surrounding the protein is larger than 80 nm(2), but not when below 30 nm(2). We also investigated the effect of external buffers on the fluorophore proton exchange rates at the ND membrane-water interfaces. With increasing buffer concentrations, the proton exchange rates were found to first decrease and then, at millimolar buffer concentrations, to increase. Monte Carlo simulations, based on a simple kinetic model of the proton exchange at the membrane-water interface, and using rate parameter values determined in our FCS experiments, could reconstruct both the observed membrane-size and the external buffer dependence. The FCS data in combination with the simulations indicate that the local proton diffusion coefficient along a membrane is ∼100 times slower than that observed over submillimeter distances by proton-pulse experiments (D(s) ∼ 10(−5)cm(2)/s), and support recent theoretical studies showing that proton diffusion along membrane surfaces is time- and length-scale dependent. The Biophysical Society 2016-05-10 2016-05-10 /pmc/articles/PMC4939474/ /pubmed/27166807 http://dx.doi.org/10.1016/j.bpj.2016.03.035 Text en © 2016 Biophysical Society. http://creativecommons.org/licenses/by/4.0/ This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Membranes
Xu, Lei
Öjemyr, Linda Näsvik
Bergstrand, Jan
Brzezinski, Peter
Widengren, Jerker
Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title_full Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title_fullStr Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title_full_unstemmed Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title_short Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers
title_sort protonation dynamics on lipid nanodiscs: influence of the membrane surface area and external buffers
topic Membranes
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4939474/
https://www.ncbi.nlm.nih.gov/pubmed/27166807
http://dx.doi.org/10.1016/j.bpj.2016.03.035
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