(757g) Correlated Membrane Bound Protein Conformational Transitions and Lipid Dynamics Provides New Insights into Leakage Kinetics By Pore Forming Proteins

Pore forming toxins are a class of cytotoxic proteins implicated in a wide range of virulent bacterial infections and diseases. These toxins bind to target membranes, undergo oligomerization to form transmembrane pores that eventually lead to cell lysis. While the protein is believed to undergo large conformational changes during assembly and pore formation, the connection between these membrane bound states and lipid reorganization during pore formation is largely unexplored. In this study, we provide a microscopic connection between pore formation, lipid dynamics and leakage kinetics by using a combination of FRET and FCS measurements and all atom molecular dynamics simulations of listeriolysin O (LLO) on single giant unilamellar vesicles. Upon exposure to LLO, two distinct populations of vesicles with widely different leakage kinetics emerge. We attribute these differences to the existence of an ensemble of oligomeric intermediates, sampling various membrane bound conformational states of the protein, and relate these to concomitant changes in lipid dynamics and leakage. Molecular dynamics simulations capture the influence of membrane bound states of a single monomer on the underlying lipid dynamics and provide molecular insights into various membrane bound states observed in the FRET experiments. Our study provides a microscopic connection between membrane binding, conformational changes and their influence on lipid reorganization which enhances our understanding protein-membrane mediated cell lysis.