The Perforin Pore Facilitates the Delivery of Cationic Cargos

Background: Perforin is a pore-forming protein that delivers granzymes to eliminate compromised cells. Results: The perforin pore preferentially delivers cationic molecules in comparison to anionic or neutrally charged cargo, which are inefficiently delivered. Conclusion: Perforin delivers cationic cargos more efficiently than anionic or neutral cargos. Significance: This is the first report of charge-based discrimination by the perforin pore.Cytotoxic lymphocytes eliminate virally infected or neoplastic cells through the action of cytotoxic proteases (granzymes). The pore-forming protein perforin is essential for delivery of granzymes into the cytoplasm of target cells; however the mechanism of this delivery is incompletely understood. Perforin contains a membrane attack complex/perforin (MACPF) domain and oligomerizes to form an aqueous pore in the plasma membrane; therefore the simplest (and best supported) model suggests that granzymes passively diffuse through the perforin pore into the cytoplasm of the target cell. Here we demonstrate that perforin preferentially delivers cationic molecules while anionic and neutral cargoes are delivered inefficiently. Furthermore, another distantly related pore-forming MACPF protein, pleurotolysin (from the oyster mushroom), also favors the delivery of cationic molecules, and efficiently delivers human granzyme B. We propose that this facilitated diffusion is due to conserved features of oligomerized MACPF proteins, which may include an anionic lumen.