Biophysical Society Thematic Meeting | Stockholm 2022

Physical and Quantitative Approaches to Overcome Antibiotic Resistance

Monday Speaker Abstracts

TEASING HALF-BILAYERS: PHYSICOCHEMICAL PROPERTIES OF LPS MONOLAYERS, ELECTROSTATIC ASYMMETRY OF LPS-PHOSPHOLIPID BILAYERS AND IMPLICATIONS FOR DRUG/PEPTIDE PERMEABILITY Sergei Sukharev 1 ; Hannah Cetuk 1 ; Jake Rosetto 1 ; Joseph Najem 4 ; Alison J Scott 2 ; Myriam L Cotten 3 ; Robert K Ernst 2 ; 1 University of Maryland, Biology, College Park, MD, USA 4 The Pennsylvania State University, Mechanical Engineering, University Park, PA, USA The outer bacterial membrane and its leaflet asymmetry were critical evolutionary inventions that allowed Gram-negative bacteria to occupy multiple ecological niches. The stratified and cross-linked structure of the outer lipopolysaccharide (LPS) leaflet functions as the major impediment for penetration of foreign substances. Yet, many drugs are characterized by a direct permeation mechanism through the LPS layer, for which partitioning/intercalation between LPS molecules is the obligatory first step. In this presentation, we focus on two major parameters of LPS layers that may affect drug intercalation: (1) the lateral compressibility and its determinants, and (2) the electrostatic potential of the LPS layer including its dominant dipole component. We analyze monolayer compression isotherms and report the molecular areas and compressibility moduli for Lipid A, Re-, Rd- and Rc-LPS isolated from E. coli, which indicate a strong influence of the carbohydrate chain length on monolayer mechanics. We report differential effects of Ca2+ and Mg2+ on the character of monolayer compression. Under high ionic strength, the surface potential of Rc-LPS was ~100 mV lower than that of E. coli phospholipids, indicating the difference in the interfacial dipole. We developed a technique allowing to reliably form completely asymmetric LPS/phospholipid droplet interface bilayers (DIBs). Consistently, the electrostatic potential difference between the LPS and phospholipid sides of asymmetric DIB was ~-110 mV, suggesting a constant electrostatic bias inside the outer bacterial membrane. Finally, we report a survey of affinities for LPS and molecular intercalation areas for seven classes of antibiotics and one class of antimicrobial peptides (Piscidins). The data reveal the stronger preference of Piscidins toward LPS as opposed to mammalian/vertebrate cell surfaces as the reason for their specificity against gram-negative microorganisms. 2 University of Maryland, School of Dentistry, Baltimore, MD, USA 3 William and Mary, Applied Science, Williamsburg, VA, USA

11