Single-molecule tracking of perfringolysin O assembly and membrane insertion uncoupling

We exploit single-molecule tracking and optical single channel recording in droplet interface bilayers to resolve the assembly pathway and pore formation of the archetypical cholesterol-dependent cytolysin nanopore, Perfringolysin O. We follow the stoichiometry and diffusion of Perfringolysin O complexes during assembly with 60 ms temporal resolution and 20 nm spatial precision. Our results suggest individual nascent complexes can insert into the lipid membrane where they continue active assembly. Overall, these data support a model of stepwise irreversible assembly dominated by monomer addition, but with infrequent assembly from larger partial complexes.