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A type VI secretion system effector delivery mechanism dependent on PAAR and a chaperone–co-chaperone complex

Nature Microbiology volume 3, pages 632–640 (2018)Cite this article

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Abstract

The type VI secretion system (T6SS) is used by many Gram-negative bacteria as a molecular weapon to modulate neighbouring bacterial and eukaryotic cells, thereby affecting the dynamics of community structure in multiple species environments. The T6SS injects its inner-needle Hcp tube, the sharpening tip complex consisting of VgrG and PAAR, and toxic effectors into neighbouring cells. Its functions are largely determined by the activities of its delivered effectors. Six mechanisms of effector delivery have been described: two mediated by the inner tube and the others mediated by the VgrG and PAAR tip complex. Here, we report an additional effector delivery mechanism that relies on interaction with a chaperone complex and a PAAR protein as a carrier. The Pseudomonas aeruginosa PAO1 TOX-REase-5 domain-containing effector TseT directly interacts with PAAR4 and the chaperone TecT for delivery, and an immunity protein, TsiT, for protection from its toxicity. TecT forms a complex with its co-chaperone, co-TecT, which is disrupted by the carboxy-terminal tail of PAAR4. In addition, we delineate a complex, multilayered competitive process that dictates effector trafficking. PAAR delivery provides an additional tool for engineering cargo protein translocation.

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Fig. 1: TOX-REase-5 effector secreted by H2-T6SS.
Fig. 2: Interactions between PAAR4, the chaperones TecT and co-TecT and the effector TseT.
Fig. 3: PAAR4 interacts with the chaperone TecT and the effector TseT through a C-terminal extension.
Fig. 4: VgrG requirement for TseT-mediated killing.
Fig. 5: Toxicity of TseT in E. coli.
Fig. 6: Model outlining the possible competing interactions that occur prior to the delivery of TseT.

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Acknowledgements

This work was supported by a Canadian Institutes of Health Research project grant, a Natural Sciences and Engineering Research Council (NSERC) Discovery grant and an Alberta Livestock and Meat Agency (ALMA) grant to T.G.D. T.G.D. is supported by a Canada Research Chair award. B.J.B. is supported by Alberta Innovates Health Solutions (AIHS) and NSERC postdoctoral fellowships. A.N.H.L. and L.L. were supported by the Markin Undergraduate Student Research Program in Health and Wellness. We thank other members of the Dong lab for providing reagents, general support and critical reading of the manuscript. We thank L. Brechenmacher and the Southern Alberta Mass Spectrometry Centre for the LC–MS/MS analysis.

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Authors and Affiliations

  1. Ecosystem and Public Health, Faculty of Veterinary Medicine; Biochemistry and Molecular Biology, Cumming School of Medicine; Snyder Institute for Chronic Diseases, University of Calgary, Calgary, Alberta, Canada

    Brianne J. Burkinshaw, Xiaoye Liang, Megan Wong, Alexander N. H. Le, Linh Lam & Tao G. Dong

  2. State Key Laboratory of Microbial Metabolism, Joint International Laboratory on Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China

    Xiaoye Liang & Tao G. Dong

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Contributions

T.G.D. conceived the project. B.J.B., X.L. and T.G.D. designed the experiments. B.J.B., X.L., M.W., A.N.H.L. and L.L. performed the experiments. B.J.B. and T.G.D. prepared the manuscript.

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Correspondence to Tao G. Dong.

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Supplementary information

Supplementary Information

Supplementary Figures 1–10, Supplementary Tables 1–3.

Reporting Summary

Supplementary Video 1

Visualization of H2-T6SS sheath assembly. Strain PAO1 retS tssB2-sfGFP was imaged over 5 minutes with a rate of 1 image per 10 seconds. The movie is played at a rate of 10 frames per second. Cells were grown to an OD600 of 2.0 in tryptic soy broth and spotted on a 0.5 × PBS agarose pad prior to imaging.

Supplementary Video 2

Deletion of vgrG2b does not affect assembly of the H2-T6SS sheath (as visualized with TssB2-sfGFP). Strain PAO1 retS tssB2-sfGFP vgrG2b was imaged over 5 minutes with a rate of 1 image per 10 seconds. The movie is played at a rate of 10 frames per second. Cells were grown to an OD600 of 2.0 in tryptic soy broth and spotted on a 0.5 × PBS agarose pad prior to imaging.

Supplementary Video 3

Deletion of vgrG4b does not affect assembly of the H2-T6SS sheath (as visualized with TssB2-sfGFP). Strain PAO1 retS tssB2-sfGFP vgrG4b was imaged over 5 minutes with a rate of 1 image per 10 seconds. The movie is played at a rate of 10 frames per second. Cells were grown to an OD600 of 2.0 in tryptic soy broth and spotted on a 0.5 × PBS agarose pad prior to imaging.

Supplementary Video 4

Deletion of vgrG6 does not affect assembly of the H2-T6SS sheath (as visualized with TssB2-sfGFP). Strain PAO1 retS tssB2-sfGFP vgrG4b was imaged over 5 minutes with a rate of 1 image per 10 seconds. The movie is played at a rate of 10 frames per second. Cells were grown to an OD600 of 2.0 in tryptic soy broth and spotted on a 0.5 × PBS agarose pad prior to imaging.

Supplementary Table 4

Samples report.

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Burkinshaw, B.J., Liang, X., Wong, M. et al. A type VI secretion system effector delivery mechanism dependent on PAAR and a chaperone–co-chaperone complex. Nat Microbiol 3, 632–640 (2018). https://doi.org/10.1038/s41564-018-0144-4

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