YscP

YscP is a protein component of the Yersinia type III secretion system (T3SS), also known as the injectisome, used by pathogenic Yersinia species to inject effector proteins into host cells. It is encoded within the Ysc-Yop virulence gene cluster on the bacterium’s virulence plasmid and is conserved across Yersinia species.

The primary known function of YscP is to act as a molecular ruler that determines the final length of the T3SS needle filament. Experimental and genetic evidence shows that the length of YscP correlates with the length of the assembled needle: longer YscP tends to produce longer needles, while shorter YscP yields shorter needles. This relationship supports a model in which the secretion system uses YscP as a timing and measuring device to regulate needle elongation.

Mechanistically, YscP is produced in the bacterial cytosol and is secreted through the growing secretion apparatus in a manner linked to needle assembly. When the needle reaches a defined length, interactions between YscP and components of the basal body or other parts of the export apparatus are thought to signal termination of elongation and to switch the system toward substrate translocation of effector proteins. The exact molecular details remain an area of active research, with multiple models proposed.

In terms of virulence, proper needle length is important for efficient translocation of Yersinia effector proteins (such as the Yops), influencing the bacterium’s ability to manipulate host cells. YscP belongs to the SctP family of T3SS ruler proteins, with homologs found in other Gram-negative bacteria that employ similar secretion systems.

See also: Type III secretion system, Yersinia pestis, Ysc-Yop gene cluster, SctP.