• Helical reconstruction of and needle filaments attached to type 3 basal bodies.

      Kotov, Vadim; Lunelli, Michele; Wald, Jiri; Kolbe, Michael; Marlovits, Thomas C; CSSB, Centre for Structural Systembiologie, Notkestr.85, 22607 Hamburg. Germany. (Elsevier, 2021-06-27)
      Gram-negative pathogens evolved a syringe-like nanomachine, termed type 3 secretion system, to deliver protein effectors into the cytoplasm of host cells. An essential component of this system is a long helical needle filament that protrudes from the bacterial surface and connects the cytoplasms of the bacterium and the eukaryotic cell. Previous structural research was predominantly focused on reconstituted type 3 needle filaments, which lacked the biological context. In this work we introduce a facile procedure to obtain high-resolution cryo-EM structure of needle filaments attached to the basal body of type 3 secretion systems. We validate our approach by solving the structure of Salmonella PrgI filament and demonstrate its utility by obtaining the first high-resolution cryo-EM reconstruction of Shigella MxiH filament. Our work paves the way to systematic structural characterization of attached type 3 needle filaments in the context of mutagenesis studies, protein structural evolution and drug development.