Rapid Membrane Disruption by a Perforin-Like Protein Facilitates Parasite Exit from Host Cells

Björn F. C. Kafsack, Janethe D. O. Pena, Isabelle Coppens, Sandeep Ravindran, John C. Boothroyd, Vern B. Carruthers, Science 2009, 323(5913):530-3.

Student: Yun-Ju Song (宋昀儒)                                     Time: 15:10~16:00 Oct. 23, 2009

Commentator: Chih-Li Lilian Hsu (胥直利 老師)      Place: Room 601

Abstract:

Egress is a pivotal step in the life cycle of intracellular pathogens initiating the transition from an expiring host cell to a fresh target cell. Previous studies reveal intracellular pathogens have evolved to produce pore-forming proteins (PFPs) that are play an important role in host cell entry, nutrient acquisition, escape from the phagolysosomal system and final egress from the host cell by a variety of prokaryotic and eukaryotic pathogens¹. However, recent study show perforin-like proteins (PLPs) are found in the genomes of intracellular parasite Toxoplasma gondii, and the mode of action or pore-forming activity has demonstrated in this study. Toxoplasma perforin-like protein 1 (TgPLP1) localized to micronemes and secreted in a calcium-dependent manner similar to other microneme proteins, which are protein important for parasites invasion. However, initial observations of TgPLP1-deficient parasite revealed the presence of parasites trapped within large spherical structures that were not seen in cultures of wild-type (WT) parasites or mutant parasites with restored expression of TgPLP1. Upon induced egress with a calcium ionophore, TgPLP1-deficient parasites activated motility and secreted microneme proteins but were significantly delayed in their time to host cell exit. Eventual escape appears to be principally due to motility-based mechanical rupture of the PVM. In addition, TgPLP1 expression was shown to be necessary for PVM permeabilization because a fluorescent protein expressed in the parasite PV failed to escape the PV upon induction of egress in the knockout. Moreover, video microscopy and immunofluorescence experiments revealed WT parasites can donate TgPLP1 to aid in escape of knockout parasites from the same cell. In vivo, TgPLP1-deficient parasites are highly attenuated (~5-log decrease in LD100) in the mouse model of toxoplasmosis. Above results are highlighting that TgPLP1 is important to rapid egress in the normal course of infection and disease and therapeutic potential of microbial egress.

References:

1.          Almeida-Campos FR, Noronha FS, Horta MF. The multitalented pore-forming proteins of intracellular pathogens. Microbes Infect 2002;4:741–50.