Electrophysiological interrogation of asymmetric droplet interface bilayers reveals surface-bound alamethicin induces lipid flip-flop |
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Authors: | Graham Taylor Mary-Anne Nguyen Subhadeep Koner Eric Freeman C. Patrick Collier Stephen A. Sarles |
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Affiliation: | 1. Department of Mechanical, Aerospace, and Biomedical Engineering, The University of Tennessee, Knoxville, TN 37996, United States;2. The Bredesen Center for Interdisciplinary Research, The University of Tennessee, Knoxville, TN 37996, United States;3. Department of Mechanical Engineering, The University of Georgia, Athens, GA, United States;4. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, United States |
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Abstract: | The droplet interface bilayer (DIB) method offers simple control over initial leaflet compositions in model membranes, enabling an experimental path to filling gaps in our knowledge about the interplay between compositional lipid asymmetry, membrane properties, and the behaviors of membrane-active species. Yet, the stability of lipid leaflet asymmetry in DIBs has received very little attention, particularly in the presence of peptides and ion channels that are often studied in DIBs. Herein, we demonstrate for the first time parallel, capacitance-based measurements of intramembrane potential with arrays of asymmetric DIBs assembled in a microfluidic device to characterize the stability of leaflet asymmetry over many hours in the presence and absence of membrane-active peptides. DIBs assembled from opposing monolayers of the ester (DPhPC) and ether (DOPhPC) forms of diphytanoyl-phosphatidylcholine yielded asymmetric bilayers with leaflet compositions that were stable for at least 18?h as indicated by a stable |137?mV| intramembrane potential. In contrast, the addition of surface-bound alamethicin peptides caused a gradual, concentration-dependent decrease in the magnitude of the dipole potential difference. Intermittent current-voltage measurements revealed that alamethicin in asymmetric DIBs also shifts the threshold voltage required to drive peptide insertion and ion channel formation. These outcomes take place over the course of 1 to 5?h after membrane formation, and suggest that alamethicin peptides promote lipid flip-flop, even in the un-inserted, surface-bound state, by disordering lipids in the monolayer to which they bind. Moreover, this methodology establishes the use of parallel electrophysiology for efficiently studying membrane asymmetry in arrays of DIBs. |
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Keywords: | Corresponding author at: Bioinspired Materials and Transduction Laboratory Department of Mechanical Aerospace and Biomedical Engineering University of Tennessee Knoxville Knoxville TN 37996 United States. |
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