Many Gram negative pathogens use the type III secretion system (T3SS) to initiate infection in eukaryotic cells. The T3SS is a highly developed macromolecular system that serves as a platform to make physical contact between host cells and pathogens and mediates the translocation of bacterial toxins into eukaryotic cells. Central to the T3SS is the mega-dalton sized, membrane embedded needle complex, composed of several proteins. However, their organization within the needle complex critical for proper assembly and function is unclear. Here, we use an integrated experimental approach that combines cryo electron microscopy with bacterial genetics, site-specific labeling, mutational analysis, chemical derivatization and high-resolution mass spectrometry to determine the topographic organization of individual components of the Salmonella typhimurium needle complex to sub-nanometer resolution and define sites critical for its stability. Our study provides insights into the organization of this evolutionary highly conserved system and is the basis for further functional analysis.

Macromolecular machines at the membrane: Dissection of the injectisome

245th National Meeting (2013)

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