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PAAR-repeat proteins sharpen and diversify the type VI secretion system spike
Mikhail M Shneider1,2, Sergey A Buth1, Brian T Ho3
1École Polytechnique Fédérale de Lausanne (EPFL), BSP-415, 1015 Lausanne, Switzerland.
Nature
|August 9, 2013
Summary
Proteins from the PAAR repeat superfamily sharpen the Type VI Secretion System (T6SS) spike, enabling bacterial cells to deliver toxins and kill prey. This discovery reveals a new model for T6SS function in bacterial predation.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- The bacterial Type VI Secretion System (T6SS) is a complex machine crucial for Gram-negative bacteria's ecological interactions.
- T6SS facilitates the delivery of toxic effectors to prokaryotic and eukaryotic cells, enabling predation.
- The precise composition and effector delivery mechanisms of T6SS remain largely unknown.
Purpose of the Study:
- To elucidate the structural role of PAAR proteins in the T6SS.
- To understand the mechanism of effector attachment and delivery by the T6SS.
- To reveal the complete architecture of the T6SS organelle for bacterial predation.
Main Methods:
- Protein structural analysis using X-ray crystallography.
- Investigating the function of PAAR proteins in T6SS-mediated secretion and killing.
- Utilizing Vibrio cholerae and Acinetobacter baylyi as model organisms.
Main Results:
- Proteins from the PAAR (proline-alanine-alanine-arginine) superfamily form a sharp, conical extension on the VgrG spike.
- PAAR proteins are essential for T6SS-mediated secretion and target cell killing in V. cholerae and A. baylyi.
- Crystal structures reveal PAAR proteins binding to VgrG-like partners, sharpening the spike complex and facilitating effector attachment.
Conclusions:
- PAAR proteins are critical components that sharpen the T6SS VgrG spike, forming a key part of the predatory apparatus.
- A new model for the T6SS organelle is proposed, where the VgrG-PAAR spike complex delivers multiple effectors simultaneously.
- This mechanism allows for efficient and simultaneous toxin delivery, enhancing bacterial predation capabilities.
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