IpaB

ipaB refers to the invasion plasmid antigen B, a virulence-associated protein found in certain enteric bacteria such as Shigella species. It is part of the ipaBCDE operon on the virulence plasmid pINV and is co-expressed with ipaC. The ipaB gene product is an abundant, secreted protein that contributes to the bacteria’s ability to invade host cells through the type III secretion system (T3SS).

In activity, IpaB collaborates with IpaC to form the translocon, a pore-like structure inserted into the host cell plasma membrane. This translocon enables the delivery of bacterial effector proteins into the host cytosol, triggering cytoskeletal rearrangements and bacterial uptake. IpaB is implicated in sensing or interacting with host membranes and works in concert with IpaC to promote membrane breach and invasion. Loss or disruption of ipaB reduces invasion efficiency and attenuates virulence in experimental models.

Expression and regulation of ipaB are governed by the virulence regulatory cascade encoded on pINV. Environmental cues, including temperature and host contact, influence transcriptional activation by regulators such as VirF and VirB. Secretion of IpaB is stimulated upon contact with host cells, aligning protein delivery with the invasion process.

Structural notes indicate that IpaB is a relatively large, membrane-associated protein that forms a functional complex with IpaC during translocon assembly. The exact stoichiometry can vary, but the IpaB–IpaC complex is central to pore formation and effector translocation.

ipaB is a widely studied virulence factor in Shigella and related pathogens, serving as a model for understanding T3SS-mediated invasion and informing research into interventions targeting invasive enteric infections.