SipB

SipB, short for Salmonella invasion protein B, is a virulence factor of Salmonella enterica, most notably associated with the typhimurium serovar. It is encoded within the Salmonella Pathogenicity Island 1 (SPI-1) and is a component of the bacterium’s type III secretion system (T3SS) used during invasion of host cells.

Function and role in infection

SipB acts as a translocator protein that collaborates with SipC to form a translocon pore in the host cell membrane. This pore enables the injection of Salmonella effector proteins into the host cell cytoplasm, which then orchestrate signaling and cytoskeletal rearrangements. The outcome is membrane ruffling and uptake of the bacteria by non-phagocytic cells, a critical step in establishing intracellular infection. SipB’s activity is coordinated with other SPI-1 invasion factors as part of a tightly regulated expression program activated under conditions encountered in the host intestinal environment.

Regulation and expression

Expression of sipB is part of the broader SPI-1 regulon. Regulatory networks involving master regulators coordinate the production of invasion proteins to ensure that SipB and its partners are available when the bacterium encounters host cells.

Clinical and research relevance

Mutations or deletions of sipB often reduce or abolish invasive capability and attenuate virulence in experimental models, highlighting SipB’s essential role in the invasion process. As a component of the Salmonella invasion machinery, SipB is a focus of studies on pathogenesis and potential strategies to mitigate infection.

See also

SPI-1, Type III secretion system, SipC, Salmonella enterica.