YscU

YscU is a protein component of the Type III secretion system (T3SS) in Yersinia species, encoded on the virulence plasmid pCD1. It is a conserved member of the SctU family and is considered part of the T3SS basal apparatus that spans the bacterial inner membrane to form the injectisome used to deliver effectors into host cells.

Functionally, YscU participates in the assembly and operation of the secretion machinery and plays a key role in substrate specificity switching. The T3SS secretes different sets of proteins in a regulated order, starting with needle and inner rod components and transitioning to translocators and effector proteins. This secretion switch is closely coordinated with needle length control and involves regulatory interactions with other components such as YscP. YscU is therefore central to timing the switch from early to late substrates.

A notable feature of YscU is autoproteolytic processing. It undergoes cleavage at a conserved site to yield N- and C-terminal fragments that remain associated within the complex. This processing is required for proper secretion switching and overall function of the system, influencing how the needle length and substrate hierarchy are controlled.

Localization and interactions place YscU in the inner membrane region of the T3SS, where it interfaces with other core components and regulatory factors. Its function is broadly conserved among Yersinia species and related bacteria, where orthologs are referred to as SctU.

Clinical relevance: Disruption of YscU impairs T3SS assembly and effector secretion, reducing virulence in Yersinia infections.