Facilitated diffusion through the perforin pore

Cytotoxic lymphocytes eliminate virally infected or neoplastic cells through the action of cytotoxic proteases (granzymes). The poreforming 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 oligomerises 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 poreforming MACPF protein, pleurotolysin (from the oyster mushroom), also favours the delivery of cationic molecules, and efficiently delivers human granzyme B. We propose that this facilitated diffusion is due to conserved features of oligomerised MACPF proteins, which may include an anionic lumen. Cytotoxic lymphocytes (CLs) eliminate infected or compromised target cells as part of the immune response. This elimination is achieved through exocytosis of lytic granules containing a pore-forming protein, perforin and the granzyme family of serine proteases (1). Granzymes induce http://www.jbc.org/cgi/doi/10.1074/jbc.M113.544890 The latest version is at JBC Papers in Press. Published on February 20, 2014 as Manuscript M113.544890 Copyright 2014 by The American Society for Biochemistry and Molecular Biology, Inc. by gest on O cber 0, 2017 hp://w w w .jb.org/ D ow nladed from Facilitated diffusion through the perforin pore