Cryo-EM structure of the Shigella type III needle complex

PLoS Pathog. 2020 Feb 24;16(2):e1008263. doi: 10.1371/journal.ppat.1008263. eCollection 2020 Feb.

Abstract

The Type III Secretion Systems (T3SS) needle complex is a conserved syringe-shaped protein translocation nanomachine with a mass of about 3.5 MDa essential for the survival and virulence of many Gram-negative bacterial pathogens. This system is composed of a membrane-embedded basal body and an extracellular needle that deliver effector proteins into host cells. High-resolution structures of the T3SS from different organisms and infection stages are needed to understand the underlying molecular mechanisms of effector translocation. Here, we present the cryo-electron microscopy structure of the isolated Shigella T3SS needle complex. The inner membrane (IM) region of the basal body adopts 24-fold rotational symmetry and forms a channel system that connects the bacterial periplasm with the export apparatus cage. The secretin oligomer adopts a heterogeneous architecture with 16- and 15-fold cyclic symmetry in the periplasmic N-terminal connector and C-terminal outer membrane ring, respectively. Two out of three IM subunits bind the secretin connector via a β-sheet augmentation. The cryo-EM map also reveals the helical architecture of the export apparatus core, the inner rod, the needle and their intervening interfaces.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / ultrastructure*
  • Cell Membrane / genetics
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure*
  • Cryoelectron Microscopy*
  • Protein Conformation, beta-Strand
  • Protein Domains
  • Shigella / genetics
  • Shigella / metabolism
  • Shigella / ultrastructure*
  • Type III Secretion Systems / genetics
  • Type III Secretion Systems / metabolism
  • Type III Secretion Systems / ultrastructure*

Substances

  • Bacterial Proteins
  • Type III Secretion Systems

Grants and funding

This work was funded by the European Research Council under the European Community’s Seventh Framework Programme(https://erc.europa.eu/) under grant number 311374. This work has been supported by iNEXT, grant number 653706, funded by the Horizon 2020 programme of the European Commission. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.