Involved in the synthesis of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:25690097). Pilot protein that is required for the proper localization of the secretin PscC in the outer membrane (PubMed:25690097). Necessary for full in vivo virulence (PubMed:25690097). Could be a lipoprotein. Displays a compact beta-sandwich fold with interdependent beta-sheets. Possesses a large patch of basic residues that could play a role in membrane recognition. Deletion of the gene causes a diminution of T3SS needles, a decrease in secretion of T3SS proteins and affects the regulatory gene operon. It reduces T3SS activity toward eukaryotic cells. Mutant shows reduced virulence in a mouse pneumonia model. Belongs to the ExsB/YscW family.