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In situ architecture, function, and evolution of a contractile injection system.
Désirée Böck1, João M Medeiros1, Han-Fei Tsao2
1Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland.
Science (New York, N.Y.)
|August 19, 2017
Summary
The type 6 secretion system (T6SS) in bacteria uses a contractile injection system for cell-cell interactions. Researchers revealed its in situ architecture and firing mechanism, suggesting broader roles in host interactions and T6SS diversity.
Area of Science:
- Microbiology
- Structural Biology
- Cell Biology
Background:
- The type 6 secretion system (T6SS) is a contractile injection machine mediating bacterial cell-cell interactions.
- Unlike extracellular systems, T6SS is intracellular and membrane-associated, resembling bacteriophage tail structures.
Purpose of the Study:
- To elucidate the in situ architecture and function of the T6SS in *Amoebophilus asiaticus*.
- To understand the conformational changes and assembly of T6SS during its firing cycle.
Main Methods:
- Cryo-focused ion beam milling
- Electron cryotomography
- Functional assays
- Evolutionary sequence analyses
Main Results:
- The T6SS architecture comprises three modules: contractile sheath-tube, baseplate, and anchor.
- Conformational changes were observed in all modules upon firing.
- Lateral baseplate interactions facilitate hexagonal array formation of T6SS.
- The system interacts with host membranes and may aid in phagosome escape.
Conclusions:
- The study provides a detailed structural and functional understanding of a bacterial T6SS.
- T6SSs are potentially more widespread in bacteria than previously recognized.
- These findings offer a foundation for exploring T6SS diversity and mechanisms.
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