Oligomerization of type III secretion proteins PopB and PopD precedes pore formation in Pseudomonas

Speaker：鄒志成

Commentator：何漣漪  老師

Time：15:00-16:00  11/05/2003

Pseudomoas aeruginosa is a Gram-negative, opportunistic pathogen, and is the causative agent of a large of number of nosocomial infections as well as acute illness in immunocompromised individuals, such AIDS, cancer and severe burn patients. P. aeruginosa employs a type III secretion system, which is common among Gram-negative bacteria, for the injection of effector molecules into the cytoplasmic compartments through a channel on the target membrane ( the “translocon” ). In this paper, the authors functionally and structurally characterize the P. aeruginosa PopB/PopD translocation channel by expressing the Pop membrane proteins complexed to their common chaperon (PcrH). PopB/PcrH and PopD/PcrH can form either as stable heterodimers or as metastable heterooligomers. Only oligomeric forms are able to bind to and disrupt cholesterol-rich membranes. This occurs within a pH range of 5-7 in the case of PopB/PcrH, and only at acidic pH for PcrH-free PopD. Electron microscopy reveals that upon membrane association PopB and PopD form 80 A wide rings which encircle 40 A wide cavities. The extensive biochemical characterization of the components of a type III secretion translocaton pore, as well as structure insight provided by electron microscopy data for the Pop system, allows us understand a model for translocon pore formation and insertion.

References：

1.      Dacheux,D., Goure,J. and Atree,I. (2001) Pore forming activity of type III system –secreted proteins leads to oncosis of Pseudomonas aeruginosa-infected macrophages. Mol. Microbiol.,40, 76-85

2.      Schoehn,G., Guilmi,AMD., and Deassen,A.. (2003) Oligomerization of type III secretion proteins PopB and PopD precedes pore formation in Pseudomonas. EMBO J., 22, 4957-4967