YopB

YopB is a hydrophobic protein component of the type III secretion system (T3SS) found in Yersinia species, including Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica. It is one of the translocator proteins that, together with YopD, forms the Yersinia translocon. When bacteria contact a host cell, YopB and YopD are secreted and insert into the host plasma membrane to assemble a pore through which effector proteins (Yops) can be translocated into the cytosol.

Genetically, yopB is carried on the virulence plasmid pYV and is co-regulated with other Yops by the transcriptional activator LcrF (VirF) and by the calcium-regulated secretory system. Expression and secretion of YopB (and YopD) are associated with the low calcium response at 37°C, conditions that promote T3SS activation and translocation.

Biochemically, YopB is a small, hydrophobic protein that localizes to the injectisome and is secreted in a complex with YopD. The translocon formed by YopB and YopD integrates into the host cell membrane and provides a conduit for Yop effectors to enter the host cell. Disruption of either YopB or YopD impairs translocation and reduces virulence, though secretion of effectors into the extracellular medium may still occur in some mutants.

In pathogenesis, YopB is essential for efficient delivery of Yop proteins into host cells and contributes to the virulence of Yersinia infections. Its function has made it a subject of study in efforts to understand T3SS mechanisms and to explore potential anti-virulence strategies.