YadA

YadA, short for Yersinia adhesin A, is a major virulence factor of certain Yersinia species, notably Yersinia enterocolitica and Yersinia pseudotuberculosis. It is encoded on the virulence plasmid pYV and functions as an autotransporter protein of the type V secretion system, forming surface-exposed adhesive structures that contribute to infection.

Structurally, YadA is anchored in the outer membrane by a C-terminal beta-barrel and presents an N-terminal passenger domain that is exported to the cell surface. The passenger domain forms a long, adhesive stalk that enables interaction with host tissues and extracellular matrix components. This architecture supports strong adherence to epithelial and endothelial surfaces and promotes autoaggregation and, in some contexts, biofilm formation.

Functionally, YadA binds extracellular matrix proteins such as collagen, laminin, and fibronectin, facilitating attachment to host cells and tissues. It also contributes to immune evasion by binding host complement regulatory proteins, aiding serum resistance and reducing complement-mediated killing. In addition, YadA can enhance colonization and dissemination by promoting bacterial clumping and stable microcolonies on mucosal surfaces.

Regulation of YadA expression is tightly controlled and influenced by environmental conditions. yadA is plasmid-encoded and its expression is upregulated in host-like conditions, such as at body temperature, with regulatory inputs including RovA and VirF family regulators in different Yersinia species. This regulated expression pattern aligns YadA production with stages of infection.

In virulence studies, yadA mutants typically show reduced adherence, colonization, and virulence in animal models, underscoring YadA’s role in establishing infection. Since its discovery in the late 20th century, YadA has served as a model for understanding autotransporter adhesins in bacterial pathogenicity.