title: Hierarchical effector protein transport by the Salmonella Typhimurium SPI-1 type III secretion system.
abstract: BACKGROUND
  Type III secretion systems (TTSS) are employed by numerous pathogenic and symbiotic bacteria to inject a cocktail of different "effector proteins" into host cells. These effectors subvert host cell signaling to establish symbiosis or disease.
  
  
  RESULTS
  We have studied the injection of SipA and SptP, two effector proteins of the invasion-associated Salmonella type III secretion system (TTSS-1). SipA and SptP trigger different host cell responses. SipA contributes to triggering actin rearrangements and invasion while SptP reverses the actin rearrangements after the invasion has been completed. Nevertheless, SipA and SptP were both pre-formed and stored in the bacterial cytosol before host cell encounter. By time lapse microscopy, we observed that SipA was injected earlier than SptP. Computer modeling revealed that two assumptions were sufficient to explain this injection hierarchy: a large number of SipA and SptP molecules compete for transport via a limiting number of TTSS; and the TTSS recognize SipA more efficiently than SptP.
  
  
  CONCLUSIONS
  This novel mechanism of hierarchical effector protein injection may serve to avoid functional interference between SipA and SptP. An injection hierarchy of this type may be of general importance, allowing bacteria to precisely time the host cell manipulation by type III effectors.
authors.affiliation: Institute of Microbiology, ETH Zürich, Zürich, Switzerland.
authors.forename: Brit
authors.initials: B
authors.lastname: Winnen
authors.forename: Markus C
authors.initials: MC
authors.lastname: Schlumberger
authors.forename: Alexander
authors.initials: A
authors.lastname: Sturm
authors.forename: Kaspar
authors.initials: K
authors.lastname: Schüpbach
authors.forename: Stefan
authors.initials: S
authors.lastname: Siebenmann
authors.forename: Patrick
authors.initials: P
authors.lastname: Jenny
authors.forename: Wolf-Dietrich
authors.initials: WD
authors.lastname: Hardt
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003198:Computer Simulation; D008856:Microscopy, Fluorescence; D021381:Protein Transport; D012486:Salmonella typhimurium / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins