Spa15 of Shigella flexneri, a third type of chaperone in the type III secretion pathway

Mol Microbiol. 2002 Mar;43(6):1533-42. doi: 10.1046/j.1365-2958.2002.02835.x.


The type III secretion (TTS) pathway is used by numerous Gram-negative pathogens to inject virulence factors into eukaryotic cells. In addition to a functional TTS apparatus, secretion of effector proteins depends upon specific chaperones. Using a two-hybrid screen in yeast and a co-purification assay in Shigella flexneri, we demonstrated that Spa15, which is encoded by an operon for components of the TTS apparatus, is associated in the cytoplasm with three proteins that are secreted by the TTS pathway, IpaA, IpgB1 and OspC3. Spa15 was found to be necessary for stability of IpgB1 but not IpaA, and for secretion of IpaA molecules that were stored in the cytoplasm but not those that were synthesized while the secretion apparatus was active. The ability of Spa15 to associate with several non-homologous secreted proteins, the presence of Spa15 homologues in other TTS systems and the location of the corresponding genes within operons for components of the TTS apparatus suggest that Spa15 belongs to a new class of TTS chaperones.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / metabolism*
  • Bacterial Outer Membrane Proteins / genetics
  • Bacterial Outer Membrane Proteins / metabolism*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • Humans
  • Mice
  • Molecular Chaperones / chemistry
  • Molecular Chaperones / genetics*
  • Molecular Chaperones / metabolism*
  • Molecular Sequence Data
  • Plasmids / genetics
  • Rabbits
  • Shigella flexneri / genetics
  • Shigella flexneri / growth & development
  • Shigella flexneri / metabolism*
  • Shigella flexneri / pathogenicity
  • Two-Hybrid System Techniques
  • Virulence / genetics


  • Antigens, Bacterial
  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • IpaA protein, Shigella flexneri
  • Molecular Chaperones
  • OspC protein
  • Spa15 protein, Shigella flexneri