PscD

PscD is a protein component of the Type III secretion system (T3SS) basal body in Gram-negative bacteria, most notably Pseudomonas aeruginosa. It is commonly described as the ortholog of SctD, a core inner membrane protein of the injectisome. The pscD gene sits within the T3SS gene cluster and is part of the operon encoding basal body and needle components. PscD is predicted to span the inner membrane and possesses a periplasmic domain that helps assemble the basal body by linking the inner membrane to the outer-membrane ring formed by the secretin PscC (SctC). It is thought to interact with cytoplasmic components such as the ATPase PscN and with other inner membrane proteins to coordinate secretion.

Disruption of pscD in P. aeruginosa often reduces effector secretion and virulence, indicating an essential role in assembly or function of the T3SS. Across diverse bacteria with T3SS, PscD homologs (SctD) are conserved inner membrane components of the basal body, reflecting a common injectisome architecture.

Structural and research notes: High-resolution structures are limited; comparative data support a two-domain organization with an N-terminal transmembrane anchor and a periplasmic region involved in basal-body interactions. The exact stoichiometry and dynamics of PscD within the basal body remain active research topics.