YscK

YscK is a protein component of the type III secretion system (T3SS) in Yersinia species, including Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis. It is encoded by the yscK gene within the core Ysc/Yersinia T3SS gene cluster and localizes to the cytoplasm near the injectisome. YscK is considered part of the cytosolic sorting platform, a multiprotein complex that coordinates substrate recognition and secretion through the T3SS apparatus.

Functionally, YscK participates in assembling and stabilizing the cytosolic sorting platform and interacts with other cytosolic T3SS components, notably YscQ (the C-ring component) and YscL, to regulate secretion activity. Through these interactions, YscK contributes to the timing and efficiency of effector export and may influence the balance between translocator and effector protein secretion.

Clinical relevance lies in the role of the T3SS as a major virulence determinant in Yersinia. Inactivation or loss of YscK impairs type III secretion and can reduce virulence in animal models, indicating its importance for pathogenicity.

Conservation and analogs: YscK is the Yersinia ortholog of SctK, a conserved T3SS component found in diverse Gram-negative bacteria. As with its counterparts, YscK is typically viewed as part of the cytosolic sorting platform that connects the ATPase and the secretion channel.

Overall, YscK is a key, conserved element of the Yersinia T3SS that supports proper assembly and regulation of the secretion system, contributing to the bacterium’s ability to deliver virulence factors.