YopO

YopO, also known as YpkA, is a virulence factor produced by pathogenic Yersinia species, including Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. It is delivered into host cells by the bacteria’s type III secretion system and functions as a serine/threonine kinase that is activated in the presence of host calcium/calmodulin.

Once translocated into host cells, YopO binds actin and uses actin as a cofactor to stimulate its kinase activity. The kinase then phosphorylates host proteins involved in cytoskeletal regulation and signaling, leading to disruption of the actin cytoskeleton and interference with processes such as phagocytosis. This activity contributes to immune evasion by impairing macrophage uptake and other host defenses, aiding bacterial survival and propagation during infection.

Genetically, YopO is encoded by the yopO gene and is often referred to in literature as YpkA, reflecting its identity within the YopO/YpkA family of type III secretion effectors. The gene is conserved among pathogenic Yersinia species, underscoring its role in virulence.

Structurally, YopO comprises an N-terminal kinase domain and a C-terminal region that mediates interactions with host factors. Structural and biochemical studies show its resemblance to eukaryotic protein kinases and highlight the requirement for calmodulin binding to achieve full enzymatic activity. Overall, YopO is an integral part of the Yersinia virulence arsenal, contributing to cytoskeletal disruption and immune modulation during infection.