YpkA

YpkA, also known as YopO, is a type III secretion system effector protein produced by pathogenic Yersinia species such as Yersinia pestis and Yersinia pseudotuberculosis. It is delivered into the host cell cytosol by the bacterium’s secretion machinery and functions as a serine/threonine kinase. The protein contains a catalytic kinase domain and a C-terminal region that supports effector activity and interaction with host cytoskeletal components.

The kinase activity of YpkA is activated by host actin and leads to phosphorylation of host proteins involved in cytoskeletal regulation. Through this activity, YpkA perturbs actin dynamics, contributing to the disruption of the actin cytoskeleton in the host cell. This disruption can interfere with normal cell processes and signaling pathways that underlie phagocytosis and other immune responses.

Biological and pathogenic roles of YpkA center on its contribution to virulence. By inhibiting phagocytosis and altering host cell signaling, YpkA supports intracellular survival and dissemination of the bacteria in the host. The importance of YpkA can vary by strain and experimental model, but mutants lacking YpkA generally show reduced virulence in animal studies.

Genetically, YpkA is one of several effector proteins used by Yersinia to manipulate host cells. Homologous kinases with similar catalytic domains are found in related species, reflecting a conserved strategy among pathogenic Yersinia to subvert host cytoskeletal regulation through actin-activated serine/threonine kinase activity.