Salmonella type III effectors PipB and PipB2 are targeted to detergent-resistant microdomains on internal host cell membranes

Speaker: 張 力 云

Commentator: 吳 俊 忠 老師

Time: PM 3:00-4:00; 12/17/2003

Place: 601

Abstract

      The Salmonella enterica type III secretion system (TTSS) encoded in Salmonella pathogenicity island 2 (SPI-2) translocates effectors across the membrane of the Salmonella-containing vacuole (SCV) (1). The authors discovered a new effector PipB2, that shows high similarity to PipB which has been identified as an effector secreted by TTSS (2). By using a specific epitope-tagging approach they found that PipB2 is translocated to the Salmonella-containing vacuole and Salmonella-induced filaments (Sifs), a tubular structure formed by the aggregation of host cell membrane, in both the macrophages and epithelial cells. The N-terminal 225-amino-acid of PipB2 is important for promoting the translocation of this protein to SCVs and Sifs. Through microtubules formation, PipB2 also can be translocated to the peripheral vesicles in epithelial cell. Both PipB and PipB2 can resist high salt, high pH and non-ionic detergent TX-100, and both of them are concentrated in the intracellular detergen-resistant microdomains (DRMs), know as lipid rafts, on the membrane of SCVs and Sifs. The location of PipB and PipB2 in the lipid rafts suggests that these two proteins may play a role in the activation or suppression of host cell signaling. The authors also found that both PipB and PipB2, unlike other effector proteins, can not be secreted into the culture supernatant. By isolation and characterization of a PipB2-deficient mutant, they demonstrated that although this protein plays no role in the intracellular proliferation of bacteria, it is involved in the pathogenicity of Salmonella (3).

References:

1.     Hansen-Wester, I., and Hensel, M. (2001) Salmonella pathogenicity islands encoding type III secretion systems. Microbes Infect 3: 549–559.

2.     Knodler, L.A., Celli, J., Hardt, W.D., Vallance, B.A., Yip, C., and Finlay, B.B. (2002) Salmonella effectors within a single pathogenicity island are differentially expressed and translocated by separate type III secretion systems. Mol Microbiol 43: 1089–1103.

3.     Knodler, L.A., Vallance, B.A., Hensel, M., Jäckel, D., Finlay, B.B., and Mortimer, O.S. (2003) Salmonella type III effectors PipB and PipB2 are targeted to detergent-resistant microdomains on internal host cell membranes. Mol Microbiol 49: 685-704.