The Solvent-Exposed C-Terminus of the Cytolysin A Pore-Forming Toxin Directs Pore Formation and Channel Function in Membranes.

Pore-forming toxins (PFTs) bind to cell membranes and form nanoscale pores that allow leakage of cellular components, resulting in cell death. The water-soluble, monomeric form of these toxins shows a dramatic conformational change during pore formation, as exemplified by crystal structures of the monomer and functional pore of cytolysin A (ClyA). The solvent-exposed, C-terminal residues of the protein are essential for activity, but the mechanism by which this region regulates pore formation remains unknown. We show here that deletion of the C-terminus of ClyA did not alter its ability to bind to the membrane or oligomerize in detergent. However, the truncated toxin lysed erythrocytes poorly, was more susceptible to proteolysis and thermal unfolding, and showed low calcein leakage from small unilamellar vesicles. Using fully atomistic molecular dynamics (MD) simulations, we find that deletion of C-terminal residues from the ClyA monomer significantly altered stability and unfolding trajectories in the tr...