InvC

invC is a bacterial gene encoding an ATPase that powers the type III secretion system (T3SS) used by Salmonella enterica, particularly within the Salmonella pathogenicity island 1 (SPI-1). The corresponding protein is a cytoplasmic ATPase related to the flagellar export ATPase FliI and to Yersinia YscN. InvC is thought to assemble as a hexameric ring and to use ATP hydrolysis to energize the unfolding and export of SPI-1 effector proteins through the secretion apparatus.

Function and mechanism

InvC provides the energy required for secretion of SPI-1 substrates across the inner membrane and through the basal body and needle complex. It interacts with multiple components of the export apparatus and coordinates substrate handling with chaperones bound to effectors in the cytosol. ATP binding and hydrolysis drive conformational changes that propel effector proteins such as SopE, SopE2, SipA, SipC, and SipB toward and through the secretion channel.

Role in virulence and regulation

As an essential component of SPI-1–encoded T3SS, invC is critical for efficient secretion and for the invasive phenotype of Salmonella in cultured cells and animal models. Mutants lacking invC typically exhibit greatly reduced or abolished effector secretion and impaired invasion of epithelial cells, contributing to attenuated virulence. Expression of SPI-1 genes, including invC, is integrated into a broader regulatory network controlled by factors such as HilA and InvF/InvE and influenced by environmental signals like temperature and osmolarity.

Structure and research significance

InvC is conserved across many T3SS-containing bacteria, underscoring its central role as an energy-transducing element of the system. Structural and functional studies of InvC and related ATPases inform understanding of secretion energetics and have positioned ATPase activity as a potential target for antivirulence strategies.

See also: Type III secretion system, SPI-1, Salmonella enterica, YscN, FliI.