Salmonella virulence protein SifA is a G protein antagonist

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 37; pp. 14141 - 14146
• Main Authors: Jackson, Laurie K, Nawabi, Parwez, Hentea, Cristiana, Roark, Everett A, Haldar, Kasturi
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 16.09.2008; National Acad Sciences
• Subjects: adsorption; air-water interface; Antagonist drugs; Antibodies; Bacteria; Bacterial proteins; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding sites; Biological Sciences; Cell Membrane - metabolism; Cells; chemical concentration; diffusion; dispersions; emulsifiers; enzymatic hydrolysis; Epithelial cells; foaming properties; food processing; functional properties; globulins; glycinin; Glycoproteins - genetics; Glycoproteins - metabolism; Guanosine Triphosphate - metabolism; HeLa cells; Hydrogen-Ion Concentration; Infections; interface phenomena; Lysosomal-Associated Membrane Protein 1 - metabolism; Membranes; physical stability; Protein Binding; protein content; protein hydrolysates; Proteins; rab GTP-Binding Proteins - antagonists & inhibitors; rab GTP-Binding Proteins - metabolism; Resins; rheological properties; Salmonella; Salmonella typhimurium - genetics; Salmonella typhimurium - metabolism; Salmonella typhimurium - pathogenicity; soy protein; surface dilatational properties; surface tension; Vacuoles; Virulence; Virulence Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0801872105

Salmonella's success at proliferating intracellularly and causing disease depends on the translocation of a major virulence protein, SifA, into the host cell. SifA recruits membranes enriched in lysosome associated membrane protein 1 (LAMP1) and is needed for growth of Salmonella induced filaments (Sifs) and the Salmonella containing vacuole (SCV). It directly binds a host protein called SKIP (SifA and kinesin interacting protein) which is critical for membrane stability and motor dynamics at the SCV. SifA also contains a WxxxE motif, predictive of G protein mimicry in bacterial effectors, but whether and how it mimics the action of a host G protein is not known. We show that SKIP's pleckstrin homology domain, which directly binds SifA, also binds to the late endosomal GTPase Rab9. Knockdown studies suggest that both SKIP and Rab9 function to maintain peripheral LAMP1 distribution in cells. The Rab9:SKIP interaction is GTP-dependent and is inhibited by SifA binding to the SKIP pleckstrin homology domain, suggesting that SifA may be a Rab9 antagonist. SifA:SKIP binding is significantly tighter than Rab9:SKIP binding and may thus allow SifA to bring SKIP to the SCV via SKIP's Rab9-binding site. Rab9 can measurably reverse SifA-dependent LAMP1 recruitment and the perinuclear location of the SCV in cells. Importantly, binding to SKIP requires SifA residues W197 and E201 of the conserved WxxxE signature sequence, leading to the speculation that bacterial G protein mimicry may result in G protein antagonism.