title: Genetically distinct pathways guide effector export through the type VI secretion system.
abstract: 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 (T6SS), 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 T6S substrates that exploits this chaperone-like quality of Hcp. Application of this approach to the Hcp secretion island I-encoded T6SS (H1-T6SS) of Pseudomonas aeruginosa led to the identification of a novel effector protein, termed Tse4 (type VI secretion exported 4), subsequently shown to act as a potent intra-specific H1-T6SS-delivered antibacterial toxin. Interestingly, our screen failed to identify two predicted H1-T6SS effectors, Tse5 and Tse6, 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 H1-T6SS-exported VgrG proteins, whereas Tse5 and Tse6 delivery strictly required a cognate VgrG. Together, we propose that interaction with either VgrG or Hcp defines distinct pathways for T6S effector export.
authors.affiliation: Department of Microbiology, University of Washington, Seattle, WA, 98195, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Whitney
authors.forename: Christina M
authors.initials: CM
authors.lastname: Beck
authors.forename: Young Ah
authors.initials: YA
authors.lastname: Goo
authors.forename: Alistair B
authors.initials: AB
authors.lastname: Russell
authors.forename: Brittany N
authors.initials: BN
authors.lastname: Harding
authors.forename: Justin A
authors.initials: JA
authors.lastname: De Leon
authors.forename: David A
authors.initials: DA
authors.lastname: Cunningham
authors.forename: Bao Q
authors.initials: BQ
authors.lastname: Tran
authors.forename: David A
authors.initials: DA
authors.lastname: Low
authors.forename: David R
authors.initials: DR
authors.lastname: Goodlett
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayes
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Mougous
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D018832:Molecular Chaperones / Q000378:metabolism*; D021381:Protein Transport; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D018832:Molecular Chaperones