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Nat Commun. 2018 Dec 19;9(1):5385. doi: 10.1038/s41467-018-07796-5.

Structure of the type VI secretion system TssK-TssF-TssG baseplate subcomplex revealed by cryo-electron microscopy.

Author information

1
Department of Biochemistry, University of Washington, Seattle, WA, 98195, USA.
2
Department of Microbiology, University of Washington, Seattle, WA, 98195, USA.
3
Architecture et Fonction des Macromolecules Biologiques, Aix-Marseille Universite, CNRS, Campus de Luminy, Case 932, 13288, Marseille, Cedex 09, France.
4
Howard Hughes Medical Institute, University of Washington, Seattle, WA, 98195, USA.
5
Department of Biochemistry, University of Washington, Seattle, WA, 98195, USA. dveesler@uw.edu.

Abstract

Type VI secretion systems (T6SSs) translocate effectors into target cells and are made of a contractile sheath and a tube docked onto a multi-protein transmembrane complex via a baseplate. Although some information is available about the mechanisms of tail contraction leading to effector delivery, the detailed architecture and function of the baseplate remain unknown. Here, we report the 3.7 Å resolution cryo-electron microscopy reconstruction of an enteroaggregative Escherichia coli baseplate subcomplex assembled from TssK, TssF and TssG. The structure reveals two TssK trimers interact with a locally pseudo-3-fold symmetrical complex comprising two copies of TssF and one copy of TssG. TssF and TssG are structurally related to each other and to components of the phage T4 baseplate and of the type IV secretion system, strengthening the evolutionary relationships among these macromolecular machines. These results, together with bacterial two-hybrid assays, provide a structural framework to understand the T6SS baseplate architecture.

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