Findings from S. Urwyler et al in legionnaire disease reported
March 2nd, 2009
2009 MAR 2 -- According to recent research published in the journal Traffic, "Legionella pneumophila, the causative agent of Legionnaires' disease, replicates in macrophages and amoebae within 'Legionella-containing vacuoles' (LCVs), which communicate with the early secretory pathway and the endoplasmic reticulum. Formation of LCVs requires the bacterial Icm/Dot type IV secretion system."
"The Icm/Dot-translocated effector protein SidC selectively anchors to LCVs by binding the host lipid phosphatidylinositol-4-phosphate (PtdIns(4) P). Here, we describe a novel and simple approach to purify intact vacuoles formed by L. pneumophila within Dictyostelium discoideum by using magnetic immunoseparation with an antibody against SidC, followed by density gradient centrifugation. To monitor LCV purification by fluorescence microscopy, we used Dictyostelium producing the LCV marker calnexin-GFP and L. pneumophila labeled with the red fluorescent protein DsRed. A proteome analysis of purified LCVs by liquid chromatography coupled to tandem mass spectrometry revealed 566 host proteins, including known LCV components, such as the small GTPases Arf1, Rab1 and Rab7. Rab8, an endosomal regulator of the late secretory pathway originating from the trans Golgi network, and the endosomal GTPase Rab14 were identified as novel LCV components, which were found to be present on vacuoles harboring wild-type but not Icm/Dot-deficient L. pneumophila. Thus, LCVs also communicate with the late secretory and endosomal pathways," wrote S. Urwyler and colleagues.
The researchers concluded: "Depletion of Rab8 or Arf1 by RNA interference reduced the amount of SidC on LCVs, indicating that the GTPases promote the recruitment of Legionella effectors by regulating the level of PtdIns(4) P."
Urwyler and colleagues published their study in Traffic (Proteome Analysis of Legionella Vacuoles Purified by Magnetic Immunoseparation Reveals Secretory and Endosomal GTPases. Traffic, 2009;10(1):76-87).
For additional information, contact H. Hilbi, ETH, Institute Microbiology, Dept. of Biology, CH-8093 Zurich, Switzerland.
The publisher's contact information for the journal Traffic is: Blackwell Publishing, 9600 Garsington Rd., Oxford OX4 2DQ, Oxon, England.
