YscF

YscF is a protein component of the type III secretion system (T3SS) in Yersinia species, including Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica. It functions as the needle subunit, polymerizing to form the extracellular needle that spans the bacterial envelope and serves as a conduit for delivering effector proteins into host cells.

In the T3SS, YscF is produced in the cytoplasm and exported through the basal body of the secretion apparatus. Secreted YscF monomers assemble into a rigid, helical needle that projects from the bacterial surface. The needle serves as a structural platform for the subsequent translocation across the host membrane and coordinates the delivery of effector proteins via the associated translocon and tip complex, including components such as LcrV.

Genetically, YscF is encoded by the yscF gene within the ysc operon, which contains multiple structural and regulatory genes of the Yersinia T3SS. Expression of yscF and other T3SS genes is tightly regulated and is typically upregulated under host-like conditions, particularly at 37°C, through the VirF/LcrF transcriptional regulator network in response to environmental cues such as temperature and calcium concentration.

Biological significance of YscF lies in its essential role for virulence. By enabling the injection of Yersinia effector proteins into host cells, YscF supports interference with host immune responses and promotes bacterial survival and pathogenicity. Disruption of YscF function impairs needle formation and effector translocation, attenuating virulence.

See also: Type III secretion system, Yersinia virulence factors.