Architecture of the outer-membrane core complex from a conjugative type IV secretion system

Nat Commun. 2021 Nov 25;12(1):6834. doi: 10.1038/s41467-021-27178-8.


Conjugation is one of the most important processes that bacteria utilize to spread antibiotic resistance genes among bacterial populations. Interbacterial DNA transfer requires a large double membrane-spanning nanomachine called the type 4 secretion system (T4SS) made up of the inner-membrane complex (IMC), the outer-membrane core complex (OMCC) and the conjugative pilus. The iconic F plasmid-encoded T4SS has been central in understanding conjugation for several decades, however atomic details of its structure are not known. Here, we report the structure of a complete conjugative OMCC encoded by the pED208 plasmid from E. coli, solved by cryo-electron microscopy at 3.3 Å resolution. This 2.1 MDa complex has a unique arrangement with two radial concentric rings, each having a different symmetry eventually contributing to remarkable differences in protein stoichiometry and flexibility in comparison to other OMCCs. Our structure suggests that F-OMCC is a highly dynamic complex, with implications for pilus extension and retraction during conjugation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Cryoelectron Microscopy
  • DNA, Bacterial
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Fimbriae, Bacterial / metabolism
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism
  • Plasmids
  • Type IV Secretion Systems / chemistry*
  • Type IV Secretion Systems / genetics
  • Type IV Secretion Systems / metabolism*


  • Bacterial Proteins
  • DNA, Bacterial
  • Membrane Proteins
  • Type IV Secretion Systems