Pore-forming toxins (PFTs) are a class of proteins implicated in a wide range of virulent bacterial infections and diseases. These toxins bind to target membranes and subsequently oligomerize to form functional pores that eventually lead to cell lysis. While the protein undergoes large conformational changes on the bilayer, the connection between intermediate oligomeric states and lipid reorganization during pore formation is largely unexplored. Cholesterol-dependent cytolysins (CDCs) are a subclass of PFTs widely implicated in food poisoning and other related infections. Using a prototypical CDC, listeriolysin O (LLO), we provide a microscopic connection between pore formation, lipid dynamics, and leakage kinetics by using a combination of Förster resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) measurements on single giant unilamellar vesicles (GUVs). Upon exposure to LLO, two distinct populations of GUVs with widely different leakage kinetics emerge. We attribute these differences to the existence of oligomeric intermediates, sampling various membrane-bound conformational states of the protein, and their intimate coupling to lipid rearrangement and dynamics. Molecular dynamics simulations capture the influence of various membrane-bound conformational states on the lipid and cholesterol dynamics, providing molecular interpretations to the FRET and FCS experiments. Our study establishes a microscopic connection between membrane binding and conformational changes and their influence on lipid reorganization during PFT-mediated cell lysis. Additionally, our study provides insights into membrane-mediated protein interactions widely implicated in cell signaling, fusion, folding, and other biomolecular processes.

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Direct observation of migration pathways of ions and a quantitative dissection of their energetics in solid polymer electrolytes (SPEs) are essential to understand the molecular origins of barriers limiting the conductivity of these novel materials. Depending upon the interplay between molecular packing and dynamics, SPEs exhibit a wide range of conductivity (10 −9 −10 −4 S/cm) at room temperature despite their common polymer matrix. Detailed molecular studies are needed to establish a precise correlation between the nature of polymer packing, dynamics, energetics, and ion conduction for rational design of SPE-based fast ion conductors. In the present article, a novel method is developed to observe directly the polymer-coupled transport pathways and associated energetics of ions in a crystalline SPE (PEO 3 :NaI). The anions follow a distinct helical path intertwined with the polymer helix to form a double-helix-like tunnel that facilitates the migration of the cations within it. The tight molecular packing and the presence of long-range correlations in the crystal facilitate collective hopping of ions with a strong coordination between the cation and anion transport. The abrupt changes in the conformation, helical pitch, and radius of gyration of the polymer accompanying ion hopping indicate a strong coupling between polymer dynamics and ion transport and reveal important clues about transport-promoting dynamical modes of polymers and associated structural changes in the crystalline SPE. The calculated free energy profiles provide accurate estimates of the activation barriers for the cation and anion transport in crystalline PEO 3 :NaI.

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