Biophysical Society Conference | Tahoe 2022

Molecular Biophysics of Membranes

Poster Abstracts

1-POS Board 1 AN EFFECTIVE ELECTRIC DIPOLE MODEL FOR VOLTAGE-INDUCED GATING OF LYSENIN Radwan Al Faouri 1,2 ; Daniel Fologea 5 ; Ralph L Henry 3 ; David Straub 6 ; Mahmoud Moradi 4 ; Qusay Alfaori 7 ; Hanan Alismail 8 ; Gregory J Salamo 2 ; 1 University of the Ozarks, Physics, Clarksville, AR, USA 2 University of Arkansas, Physics, Fayetteville, AR, USA 3 University of Arkansas, Biological Sciences, Fayetteville, AR, USA 4 University of Arkansas, Biochemistry, Fayetteville, AR, USA 5 Boise State University, Physics, Boise, ID, USA 6 University of Arkansas for Medical Sciences, Department of Biochemistry and Molecular Biology, Little Rock, AR, USA 7 Texas Tech University/Health Science Center/El Paso, Medical School/Education, El Paso, TX, USA 8 King Saud bin Abdulaziz University for Health Sciences, Health Sciences, Al Riyadh, Saudi Arabia Lysenin is a pore-forming toxin, which self-inserts open channels into Sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. The study’s objective is to understand the mechanism of lysenin voltage-gating. Here, we have employed a novel experimental technique to examine a model for voltage gating, that is based on the existence of an “effective electric dipole” inspired by recent reported structures of lysenin. We support this mechanism by the observations that (i) the charge-reversal and neutralization substitutions in lysenin result in changing its electrical gating properties by modifying the strength of the dipole, and (ii) an increase in the viscosity of the solvent increases the drag force and slows down the gating. Experiments were conducted by using bilayer lipid membrane (BLM) to host lysenin channels. Lipid was made of Asolectin from soybean, Sphingomyelin, and Cholesterol all were dissolved in n-Decane. The BLM was built across a small hole that is made in a Teflon partition and bathed in NaCl electrolyte solution. A protein named lysenin was used to make channels in the BLM structure, and by electrophysiology, we were able to measure the electrical activities across the BLM. An electrostatic surface representation of the lysenin monomer showed a distribution of a fixed charges revealing additional physical features of the channel structure. Our results support a model in which an internal effective electric dipole within lysenin pore forming module interacts with an applied electric field across the pore. This interaction induces a torque on the dipole that aligns it the direction of the applied field, causing motion that closes the pore. The lysenin voltage-gating mechanism depends on the negatively charged glutamates at positions Glu84 and Glu85 which create an effective electric diploe.

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