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Elife. 2017 Dec 27;6. pii: e30483. doi: 10.7554/eLife.30483.

Cryo-EM structure of the bifunctional secretin complex of Thermus thermophilus.

Author information

1
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt, Germany.
2
Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, Frankfurt, Germany.
3
Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt, Germany.
4
Sofja Kovalevskaja Group, Max Planck Institute of Biophysics, Frankfurt, Germany.
5
Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany.

Abstract

Secretins form multimeric channels across the outer membrane of Gram-negative bacteria that mediate the import or export of substrates and/or extrusion of type IV pili. The secretin complex of Thermus thermophilus is an oligomer of the 757-residue PilQ protein, essential for DNA uptake and pilus extrusion. Here, we present the cryo-EM structure of this bifunctional complex at a resolution of ~7 Å using a new reconstruction protocol. Thirteen protomers form a large periplasmic domain of six stacked rings and a secretin domain in the outer membrane. A homology model of the PilQ protein was fitted into the cryo-EM map. A crown-like structure outside the outer membrane capping the secretin was found not to be part of PilQ. Mutations in the secretin domain disrupted the crown and abolished DNA uptake, suggesting a central role of the crown in natural transformation.

KEYWORDS:

Thermus thermophilus; biophysics; cryo-electron microscopy; natural transformation; pilus; secretin; structural biology

PMID:
29280731
PMCID:
PMC5745081
DOI:
10.7554/eLife.30483
[Indexed for MEDLINE]
Free PMC Article

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