Establishing the Secretion Hierarchy

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Science  04 Mar 2011:
Vol. 331, Issue 6021, pp. 1147-1148
DOI: 10.1126/science.1203195

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Type III protein secretion systems (T3SSs) are specialized complexes of molecules in Gram-negative bacteria that mediate the introduction of virulence proteins directly into eukaryotic host cells. These supramolecular structures span the bacterial membranes, cross the extracellular space, and penetrate host cell membranes. The proper function of these systems depends on sequential secretion of the needle components, the proteins that enable translocation across the host cell membrane (translocases), and the effector proteins that carry out virulence functions (1). How this hierarchical process is regulated, however, has been unclear. On page 1188 of this issue, Lara-Tejero et al. (2) demonstrate that a large complex of T3SS proteins in Salmonella enterica serovar Typhimurium serves to sort components of the system for secretion in the appropriate sequence. Also, on page 1192, Schraidt and Marlovits (3) define the precise symmetry and stoichiometry of proteins that constitute the base of the needle complex.