Forum 01/20/2005

“Armed Bacteria: Structural Insights Into the Assembly of the Type III Secretion Needle Complex”

Thomas Marlovits, Ph.D. – Project Leader Dept of Molecular Biophysics, Yale Univ. School of Medicine

Type III secretion systems (TTSSs) mediate translocation of virulence factors into host cells. We report the 17-angstrom resolution structures of a central component of Salmonella typhimurium TTSS, the needle complex, and its assembly precursor, the bacterial envelope-anchored base. Both the base and the fully assembled needle complex adopted multiple oligomeric states in vivo, and needle assembly was accompanied by recruitment of the protein PrgJ as a structural component of the base. Moreover, conformational changes during needle assembly created scaffolds for anchoring both PrgJ and the needle substructure and may provide the basis for substrate-specificity switching during type III secretion.