Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Poster Abstracts

58-POS Board 58 DRUNKEN LIPOSOMES: MECHANISMS OF ALCOHOL-ALTERED MEMBRANE FUSION Dixon J Woodbury 1,2 ; Robert E Coffman 2 ; 1 Brigham Young University, Physiology and Develop. Biol., Provo, Utah, USA 2 Brigham Young University, Neuroscience Center, Provo, Utah, USA Ethanol intoxication in humans is thought to act primarily through interactions with membrane protein receptors, however we recently showed that short-chain alcohols dramatically alter liposome fusion rates to a planar membrane (Paxman et al. 2017. Biophys J. 112:121-132) reopening a previously long-studied possible target for ethanol. Objective: To determine the mechanisms whereby alcohols alter the fusion of liposomes to a planar membrane. Methods: We used the nystatin/ergosterol fusion assay, differential scanning calorimetry (DSC), and molecular dynamics (MD) to measure membrane-membrane and alcohol-membrane interactions. Results: Previously we showed that ethanol excites fusion when applied on the cis (liposome) side, and inhibits on the trans (extracellular) side. Presumably, excitation is due to lowering the activation energy of fusion by alcohol acting on the vesicular membrane and inhibition is due to a slight rise in activation energy due to alcohol in the planar membrane. We expected symmetric addition to excite fusion similar to cis addition, since in both cases alcohol has access to both membranes. However, symmetric addition generally decreases fusion rates, more similar to trans addition. Since fusion in our protein-free model system is driven by an osmotic gradient (high cis ), we now hypothesize that alcohol’s action in planar membranes is modified by water movement through the membrane. When alcohol is added trans , water movement aids its entry into the planar membrane where it strongly inhibits fusion. But with cis addition, water movement tends to flush alcohol out of the membrane decreasing the inhibition and allowing excitation, due to action on the vesicle membrane, to dominate. Measurements of fusion rates with decreased osmotic gradients are consistent with this hypothesis. Conclusions : Alcohols, and especially ethanol, alter membrane-membrane interactions in a way that significantly changes fusion rates at physiologically relevant doses.

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