Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Poster Abstracts

3-POS Board 3 Fluctuation Analysis of Nonequilibrium Membranes Reveals Lipid-Protein Interactions Tripta Bhatia 1 , Allan Hansen 1 , Michael Lomholt 1 , Flemming Cornelius 2 , Ole Mouritsen 1 .John Ipsen 1 . 1 MEMPHYS, University of Southern Denmark, Odense, Denmark, 2 Aarhus University, Aarhus, Denmark. The flicker data is analyzed on the basis of a phenomenological model of membrane fluctuations with Na/K pump activity. The description allows us to determine the coupling mechanism between protein activity and membrane fluctuations. Board 6 Local pH Differences at Respiratory Active Mitochondrial Membrane Proteins in Cellula Bettina Rieger 1 , Iven Winkelmann 2,1 , Daria Shalaeva 1,3 , Armen Mulkidjanian 1,3 , Wolfgang Junge 1 . Karin Busch 4,1 , 4 University of Münster, Münster, Germany. 1 University of Osnabrück, Osnabrück, Germany, 3 Lomonosov University, Moscow, Russian Federation, 2 University of Stockholm, Stockholm, Sweden, On central task of bioenergetics is the production of ATP by use of ion gradients across membranes. In mitochondria, oxidative phosphorylation (OXPHOS) is such a coupled process. Complex IV, cytochrome c oxidase, pumps protons from the N- to the positively charged P-side of the inner membrane. Complex V, the FOF1 ATP synthase, generates ATP by allowing protons to flow back across two half channels in its FO subunit. We show by use of site-directed fusion of the sensor pHLuorin, a pH-sensitive GFP derivative, that a lateral proton gradient exists between the proton source CIV, and the proton sink CV in the steady state. Furthermore, we characterize the nano-environment of active cytochrome c oxidase, CIV, in living cells, in more detail. By use of subunit-attached pH probes we report a lower pH value at a subunit of CIV next to the membrane than at a subunit oriented towards the bulk phase. In addition, the fluorescent lifetime of pHLuorin near the membrane was reduced indicating a different nano-environment. Together our data obtained from in situ measurements under physiological conditions suggest that a diffusion-controlled lateral proton gradient exists between two integrated membrane proteins, one operational as proton source and the other as proton consumer. Furthermore, for the first time, we experimentally demonstrate a second pH gradient between membrane and bulk phase. The Mitchell concept of a constant proton motive force in a single microcompartment is challenged by these results. 6-POS

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