Author: ["L. J. Worrall","C. Hong","M. Vuckovic","W. Deng","J. R. C. Bergeron","D. D Majewski","R. K. Huang","T. Spreter","B. B. Finlay","Z. Yu","N. C. J. Strynadka"]
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Abstract
The authors report the structure of the assembled membrane spanning ring forming proteins of the Salmonella Typhimurium injectisome basal body, including the first atomic structure of a member of the secretin family of outer-membrane pores. This study is a tour de force of cryo-electron microscopy, presenting direct experimental atomic structures of the assembled inner-membrane rings as well as of the outer-membrane secretin of the basal body of the Salmonella enterica serovar Typhimurium type III secretion (T3S) injectisome. The T3S injectisome is a syringe-shaped macromolecular complex that facilitates the direct delivery of bacterial virulence effectors to the host-cell cytoplasm. This is the first high-resolution structural characterization of the basal body in the assembled state and could usher in a new era of research into the mechanisms of T3S system. The type III secretion (T3S) injectisome is a specialized protein nanomachine that is critical for the pathogenicity of many Gram-negative bacteria, including purveyors of plague, typhoid fever, whooping cough, sexually transmitted infections and major nosocomial infections. This syringe-shaped 3.5-MDa macromolecular assembly spans both bacterial membranes and that of the infected host cell. The internal channel formed by the injectisome allows for the direct delivery of partially unfolded virulence effectors into the host cytoplasm1. The structural foundation of the injectisome is the basal body, a molecular lock-nut structure composed predominantly of three proteins that form highly oligomerized concentric rings spanning the inner and outer membranes2,3,4,5. Here we present the structure of the prototypical Salmonella enterica serovar Typhimurium pathogenicity island 1 basal body, determined using single-particle cryo-electron microscopy, with the inner-membrane-ring and outer-membrane-ring oligomers defined at 4.3 Å and 3.6 Å resolution, respectively. This work presents the first, to our knowledge, high-resolution structural characterization of the major components of the basal body in the assembled state, including that of the widespread class of outer-membrane portals known as secretins.Cite this article
Worrall, L., Hong, C., Vuckovic, M. et al. Near-atomic-resolution cryo-EM analysis of the Salmonella T3S injectisome basal body. Nature 540, 597–601 (2016). https://doi.org/10.1038/nature20576 