Stoichiometry of the bacterial type III secretion export apparatus

ABSTRACT: Bacterial type III secretion systems are cell envelope-spanning effector protein-delivery machines essential for colonization and survival of many Gram-negative pathogens and symbionts. The membrane-embedded core unit of these secretion systems is termed needle complex. The needle complex is composed of a base that anchors the machinery to the inner and outer membranes, a hollow filament formed by inner rod and needle subunits that serves as conduit for substrate proteins, and a membrane-embedded export apparatus facilitating substrate translocation. While the stoichiometry of the base and of the major export apparatus protein have been revealed by structural analyses, the stoichiometries of the other export apparatus components and of the inner rod remain unknown. We employed peptide concatenated standard and absolute quantification-based strategies to analyze the stoichiometry of the entire needle complex by mass spectrometry. Here we provide evidence that the export apparatus of the type III secretion system encoded on Salmonella pathogenicity island 1 contains 5 SpaP, 1 SpaQ, 1 SpaR, and 1 SpaS. We have corroborated the previously suggested stoichiometry of 9 InvA per needle complex and describe a loose association of InvA with other needle complex components that may reflect its function. These numbers indicate that the inner membrane patch of the needle complex base houses 104 transmembrane domains in total, a dense assembly whose function in the secretion process we merely understand. Furthermore, we present evidence that not more than 6 PrgJ form the inner rod of the needle complex.

INSTRUMENT(S):

ORGANISM(S): Salmonella Enterica Subsp. Enterica Serovar Typhimurium Str. Sl1344

SUBMITTER: Nicolas Nalpas  

LAB HEAD: Samuel Wagner

PROVIDER: PXD003113 | Pride | 2016-02-25

REPOSITORIES: Pride