In vivo TssA proximity labelling during type VI secretion biogenesis reveals TagA as a protein that stops and holds the sheath

Nat Microbiol. 2018 Nov;3(11):1304-1313. doi: 10.1038/s41564-018-0234-3. Epub 2018 Oct 1.


The type VI secretion system (T6SS) is a multiprotein weapon used by bacteria to destroy competitor cells. The T6SS contractile sheath wraps an effector-loaded syringe that is injected into the target cell. This tail structure assembles onto the baseplate that is docked to the membrane complex. In enteroaggregative Escherichia coli, TssA plays a central role at each stage of the T6SS assembly pathway by stabilizing the baseplate and coordinating the polymerization of the tail. Here we adapted an assay based on APEX2-dependent biotinylation to identify the proximity partners of TssA in vivo. By using stage-blocking mutations, we define the temporal contacts of TssA during T6SS biogenesis. This proteomic mapping approach also revealed an additional partner of TssA, TagA. We show that TagA is a cytosolic protein tightly associated with the membrane. Analyses of sheath dynamics further demonstrate that TagA captures the distal end of the sheath to stop its polymerization and to maintain it under the extended conformation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytoplasm / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Metalloendopeptidases / genetics
  • Metalloendopeptidases / metabolism*
  • Models, Molecular
  • Polymerization
  • Protein Conformation
  • Protein Interaction Maps
  • Proteomics
  • Type VI Secretion Systems / biosynthesis*
  • Type VI Secretion Systems / chemistry


  • Escherichia coli Proteins
  • TssA protein, E coli
  • Type VI Secretion Systems
  • Metalloendopeptidases
  • StcE protein, E coli