TssA: The cap protein of the Type VI secretion system tail

Bioessays. 2017 Oct;39(10). doi: 10.1002/bies.201600262. Epub 2017 Aug 17.


The Type VI secretion system (T6SS) is a multiprotein and mosaic apparatus that delivers protein effectors into prokaryotic or eukaryotic cells. Recent data on the enteroaggregative Escherichia coli (EAEC) T6SS have provided evidence that the TssA protein is a key component during T6SS biogenesis. The T6SS comprises a trans-envelope complex that docks the baseplate, a cytoplasmic complex that represents the assembly platform for the tail. The T6SS tail is structurally, evolutionarily and functionally similar to the contractile tails of bacteriophages. We have shown that TssA docks to the membrane complex, recruits the baseplate complex and initiates and coordinates the polymerization of the inner tube with that of the sheath. Here, we review these recent findings, discuss the variations within TssA-like proteins, speculate on the role of EAEC TssA in T6SS biogenesis and propose future research perspectives.

Keywords: TssA; bacteriophage; chaperone; contractile machine; protein transport; tail; type VI secretion.

Publication types

  • Review

MeSH terms

  • Bacteriophages / metabolism
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / metabolism
  • Type VI Secretion Systems / metabolism*


  • Escherichia coli Proteins
  • Type VI Secretion Systems