1. Rab1 guanine nucleotide exchange factor SidM is a major phosphatidylinositol 4-phosphate-binding effector protein of Legionella pneumophila.
- Author
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Brombacher E, Urwyler S, Ragaz C, Weber SS, Kami K, Overduin M, and Hilbi H
- Subjects
- Animals, Bacterial Proteins genetics, Bacterial Proteins metabolism, Carrier Proteins genetics, Carrier Proteins metabolism, Cell Line, Drosophila, Guanine Nucleotide Exchange Factors genetics, Guanine Nucleotide Exchange Factors metabolism, Humans, Legionella pneumophila genetics, Legionella pneumophila metabolism, Legionella pneumophila pathogenicity, Legionnaires' Disease genetics, Legionnaires' Disease metabolism, Mutation, Peptide Mapping, Phagocytes metabolism, Phagocytes microbiology, Phosphatidylinositol Phosphates genetics, Phosphatidylinositol Phosphates metabolism, Protein Binding physiology, Protein Structure, Tertiary physiology, Vacuoles genetics, Vacuoles metabolism, Vacuoles microbiology, rab1 GTP-Binding Proteins genetics, rab1 GTP-Binding Proteins metabolism, Bacterial Proteins chemistry, Carrier Proteins chemistry, Guanine Nucleotide Exchange Factors chemistry, Legionella pneumophila chemistry, Phosphatidylinositol Phosphates chemistry, rab1 GTP-Binding Proteins chemistry
- Abstract
The causative agent of Legionnaires disease, Legionella pneumophila, forms a replicative vacuole in phagocytes by means of the intracellular multiplication/defective organelle trafficking (Icm/Dot) type IV secretion system and translocated effector proteins, some of which subvert host GTP and phosphoinositide (PI) metabolism. The Icm/Dot substrate SidC anchors to the membrane of Legionella-containing vacuoles (LCVs) by specifically binding to phosphatidylinositol 4-phosphate (PtdIns(4)P). Using a nonbiased screen for novel L. pneumophila PI-binding proteins, we identified the Rab1 guanine nucleotide exchange factor (GEF) SidM/DrrA as the predominant PtdIns(4)P-binding protein. Purified SidM specifically and directly bound to PtdIns(4)P, whereas the SidM-interacting Icm/Dot substrate LidA preferentially bound PtdIns(3)P but also PtdIns(4)P, and the L. pneumophila Arf1 GEF RalF did not bind to any PIs. The PtdIns(4)P-binding domain of SidM was mapped to the 12-kDa C-terminal sequence, termed "P4M" (PtdIns4P binding of SidM/DrrA). The isolated P4M domain is largely helical and displayed higher PtdIns(4)P binding activity in the context of the alpha-helical, monomeric full-length protein. SidM constructs containing P4M were translocated by Icm/Dot-proficient L. pneumophila and localized to the LCV membrane, indicating that SidM anchors to PtdIns(4)P on LCVs via its P4M domain. An L. pneumophila DeltasidM mutant strain displayed significantly higher amounts of SidC on LCVs, suggesting that SidM and SidC compete for limiting amounts of PtdIns(4)P on the vacuole. Finally, RNA interference revealed that PtdIns(4)P on LCVs is specifically formed by host PtdIns 4-kinase IIIbeta. Thus, L. pneumophila exploits PtdIns(4)P produced by PtdIns 4-kinase IIIbeta to anchor the effectors SidC and SidM to LCVs.
- Published
- 2009
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