Abstract
A widespread strategy employed by pathogens to establish infection is to inhibit host-cell protein synthesis. Legionella pneumophila, an intracellular bacterial pathogen and the causative organism of Legionnaires’ disease, secretes a subset of protein effectors into host cells that inhibit translation elongation. Mechanistic insights into how the bacterium targets translation elongation remain poorly defined. We report here that the Legionella effector SidI functions in an unprecedented way as a transfer-RNA mimic that directly binds to and glycosylates the ribosome. The 3.1 Å cryo-electron microscopy structure of SidI reveals an N-terminal domain with an ‘inverted L’ shape and surface-charge distribution characteristic of tRNA mimicry, and a C-terminal domain that adopts a glycosyl transferase fold that licenses SidI to utilize GDP–mannose as a sugar precursor. This coupling of tRNA mimicry and enzymatic action endows SidI with the ability to block protein synthesis with a potency comparable to ricin, one of the most powerful toxins known. In Legionella-infected cells, the translational pausing activated by SidI elicits a stress response signature mimicking the ribotoxic stress response, which is activated by elongation inhibitors that induce ribosome collisions. SidI-mediated effects on the ribosome activate the stress kinases ZAKα and p38, which in turn drive an accumulation of the protein activating transcription factor 3 (ATF3). Intriguingly, ATF3 escapes the translation block imposed by SidI, translocates to the nucleus and orchestrates the transcription of stress-inducible genes that promote cell death, revealing a major role for ATF3 in the response to collided ribosome stress. Together, our findings elucidate a novel mechanism by which a pathogenic bacterium employs tRNA mimicry to hijack a ribosome-to-nuclear signalling pathway that regulates cell fate.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1600-1615 |
| Number of pages | 16 |
| Journal | Nature Cell Biology |
| Volume | 25 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 2023 |
Funding
We thank all of the members of the S.M. and P.W. laboratories for their critical evaluation and discussions of the data. We thank Z.-Q. Luo for his gift of isogenic ΔsidI and SidI-complemented L. pneumophila strains. We thank S. Venkatraman and L. Calviello from the Floor laboratory for helpful discussions. We thank B. Al-Sady and E. Simental from the Al-Sady laboratory for help with radioactivity experiments. We thank J. Yee from the Spitzer laboratory for help with flow cytometry experiments. We thank J. Noack, C. J. Sarabia and B. Wang for technical assistance with the project. L.W. acknowledges a fellowship from the Damon Runyon Cancer Research Foundation (DRG-2312-17). S.S. is supported by a Helen Hay Whitney Postdoc fellowship and K99 grant (grant no. 1K99GM143527-01A1) from NIGMS. N.J.K. acknowledges financial support from the National Institutes of Health (grant no. U19 AI135990). A.L.B. acknowledges financial support from the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation. S.N.F. is a Pew Scholar in the Biomedical Sciences, supported by The Pew Charitable Trusts and acknowledges financial support from the National Institutes of Health (grant no. DP2GM132932). A. Sil acknowledges financial support from the National Institutes of Health (grant no. R01AI136735) and a gift fund from the Chan Zuckerberg Biohub. P.W. acknowledges financial support from the National Institutes of Health (grant no. R01GM032384) and the Howard Hughes Medical Institute. S.M. acknowledges financial support from the National Institutes of Health (grant nos R01GM140440 and R01GM144378), the Pew Charitable Trust (grant no. A129837), a Bowes Biomedical Investigator award and a gift fund from the Chan–Zuckerberg Biohub. We thank the Vincent J. Coates Genomics Sequencing Laboratory at the California Institute for Quantitative Biosciences (QB3) for help with the RNA-seq experiments. We also thank the QB3 shared cluster for computational support. We thank all of the members of the S.M. and P.W. laboratories for their critical evaluation and discussions of the data. We thank Z.-Q. Luo for his gift of isogenic ΔsidI and SidI-complemented L. pneumophila strains. We thank S. Venkatraman and L. Calviello from the Floor laboratory for helpful discussions. We thank B. Al-Sady and E. Simental from the Al-Sady laboratory for help with radioactivity experiments. We thank J. Yee from the Spitzer laboratory for help with flow cytometry experiments. We thank J. Noack, C. J. Sarabia and B. Wang for technical assistance with the project. L.W. acknowledges a fellowship from the Damon Runyon Cancer Research Foundation (DRG-2312-17). S.S. is supported by a Helen Hay Whitney Postdoc fellowship and K99 grant (grant no. 1K99GM143527-01A1) from NIGMS. N.J.K. acknowledges financial support from the National Institutes of Health (grant no. U19 AI135990). A.L.B. acknowledges financial support from the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation. S.N.F. is a Pew Scholar in the Biomedical Sciences, supported by The Pew Charitable Trusts and acknowledges financial support from the National Institutes of Health (grant no. DP2GM132932). A. Sil acknowledges financial support from the National Institutes of Health (grant no. R01AI136735) and a gift fund from the Chan Zuckerberg Biohub. P.W. acknowledges financial support from the National Institutes of Health (grant no. R01GM032384) and the Howard Hughes Medical Institute. S.M. acknowledges financial support from the National Institutes of Health (grant nos R01GM140440 and R01GM144378), the Pew Charitable Trust (grant no. A129837), a Bowes Biomedical Investigator award and a gift fund from the Chan–Zuckerberg Biohub. We thank the Vincent J. Coates Genomics Sequencing Laboratory at the California Institute for Quantitative Biosciences (QB3) for help with the RNA-seq experiments. We also thank the QB3 shared cluster for computational support.
ASJC Scopus subject areas
- Cell Biology