The purified Shigella IpaB and Salmonella SipB translocators share biochemical properties and membrane topology

Mol Microbiol. 2003 Jul;49(2):425-39. doi: 10.1046/j.1365-2958.2003.03559.x.


An essential early event in Shigella and Salmonella pathogenesis is invasion of non-phagocytic intestinal epithelial cells. Pathogen entry is triggered by the delivery of multiple bacterial effector proteins into target mammalian cells. The Shigella invasion plasmid antigen B (IpaB), which inserts into the host plasma membrane, is required for effector delivery and invasion. To investigate the biochemical properties and membrane topology of IpaB, we purified the native full-length protein following expression in laboratory Escherichia coli. Purified IpaB assembled into trimers via an N-terminal domain predicted to form a trimeric coiled-coil, and is predominantly alpha-helical. Upon lipid interaction, two transmembrane domains (residues 313-333 and 399-419) penetrate the bilayer, allowing the intervening hydrophilic region (334-398) to cross the membrane. Purified IpaB integrated into model, erythrocyte and mammalian cell membranes without disrupting bilayer integrity, and induced liposome fusion in vitro. An IpaB-derived 162 residue alpha-helical polypeptide (IpaB(418-580)) is a potent inhibitor of IpaB-directed liposome fusion in vitro and blocked Shigella entry into cultured mammalian cells at 10(-8) M. It is also a heterologous inhibitor of Salmonella invasion protein B (SipB) activity and Salmonella entry. In contrast, IpaB(418-580) failed to prevent the contact-dependent haemolytic activity of Shigella. These findings question the proposed direct link between contact-dependent haemolysis and Shigella entry, and demonstrate that IpaB and SipB share biochemical properties and membrane topology, consistent with a conserved mode of action during cell entry.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / isolation & purification
  • Bacterial Proteins / metabolism*
  • Cell Membrane / metabolism*
  • Circular Dichroism
  • Electrophysiology
  • HeLa Cells
  • Humans
  • Liposomes / metabolism
  • Membrane Fusion
  • Membrane Proteins / chemistry
  • Membrane Proteins / isolation & purification
  • Membrane Proteins / metabolism*
  • Protein Structure, Secondary
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Salmonella / metabolism*
  • Shigella / metabolism*


  • Bacterial Proteins
  • Liposomes
  • Membrane Proteins
  • Recombinant Proteins
  • invasion protein B, Salmonella typhimurium
  • ipaB protein, Shigella