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Genetically distinct pathways guide effector export through the type VI secretion system

2014; Wiley; Volume: 92; Issue: 3 Linguagem: Inglês

10.1111/mmi.12571

1365-2958

John C. Whitney, Christina M. Beck, Young Ah Goo, Alistair B. Russell, Brittany N. Harding, Justin A. De Leon, David A. Cunningham, Bao Tran, David A. Low, David R. Goodlett, Christopher S. Hayes, Joseph D. Mougous,

Escherichia coli research studies

Summary Bacterial secretion systems often employ molecular chaperones to recognize and facilitate export of their substrates. Recent work demonstrated that a secreted component of the type VI secretion system ( T 6 SS ), haemolysin co‐regulated protein ( Hcp ), binds directly to effectors, enhancing their stability in the bacterial cytoplasm. Herein, we describe a quantitative cellular proteomics screen for T 6 S substrates that exploits this chaperone‐like quality of Hcp . Application of this approach to the Hcp secretion island I ‐encoded T 6 SS ( H 1‐ T 6 SS ) of P seudomonas aeruginosa led to the identification of a novel effector protein, termed Tse 4 ( t ype VI s ecretion e xported 4), subsequently shown to act as a potent intra‐specific H 1‐ T 6 SS ‐delivered antibacterial toxin. Interestingly, our screen failed to identify two predicted H 1‐ T 6 SS effectors, Tse 5 and Tse 6, which differ from Hcp ‐stabilized substrates by the presence of toxin‐associated PAAR ‐repeat motifs and genetic linkage to members of the valine‐glycine repeat protein G ( vgrG ) genes. Genetic studies further distinguished these two groups of effectors: Hcp ‐stabilized effectors were found to display redundancy in interbacterial competition with respect to the requirement for the two H 1‐ T 6 SS ‐exported VgrG proteins, whereas Tse 5 and Tse 6 delivery strictly required a cognate VgrG . Together, we propose that interaction with either VgrG or Hcp defines distinct pathways for T 6 S effector export.