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Science. 2017 Aug 18;357(6352):713-717. doi: 10.1126/science.aan7904.

In situ architecture, function, and evolution of a contractile injection system.

Author information

1
Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
2
Division of Microbial Ecology, University of Vienna, A-1090 Vienna, Austria.
3
Division of Microbial Ecology, University of Vienna, A-1090 Vienna, Austria. horn@microbial-ecology.net pilhofer@biol.ethz.ch.
4
Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland. horn@microbial-ecology.net pilhofer@biol.ethz.ch.

Abstract

Contractile injection systems mediate bacterial cell-cell interactions by a bacteriophage tail-like structure. In contrast to extracellular systems, the type 6 secretion system (T6SS) is defined by intracellular localization and attachment to the cytoplasmic membrane. Here we used cryo-focused ion beam milling, electron cryotomography, and functional assays to study a T6SS in Amoebophilus asiaticus The in situ architecture revealed three modules, including a contractile sheath-tube, a baseplate, and an anchor. All modules showed conformational changes upon firing. Lateral baseplate interactions coordinated T6SSs in hexagonal arrays. The system mediated interactions with host membranes and may participate in phagosome escape. Evolutionary sequence analyses predicted that T6SSs are more widespread than previously thought. Our insights form the basis for understanding T6SS key concepts and exploring T6SS diversity.

PMID:
28818949
DOI:
10.1126/science.aan7904
[Indexed for MEDLINE]

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