TY - JOUR T1 - A <em>Legionella</em> toxin mimics tRNA and glycosylates the translation machinery to trigger a ribotoxic stress response JF - bioRxiv DO - 10.1101/2022.06.10.495705 SP - 2022.06.10.495705 AU - Advait Subramanian AU - Lan Wang AU - Tom Moss AU - Mark Voorhies AU - Smriti Sangwan AU - Erica Stevenson AU - Ernst H. Pulido AU - Samentha Kwok AU - Nevan J. Krogan AU - Danielle L. Swaney AU - Stephen N. Floor AU - Anita Sil AU - Peter Walter AU - Shaeri Mukherjee Y1 - 2022/01/01 UR - http://biorxiv.org/content/early/2022/06/11/2022.06.10.495705.abstract N2 - Pathogens often secrete proteins or nucleic acids that mimic the structure and/or function of molecules expressed in their hosts. Molecular mimicry empowers pathogens to subvert critical host processes and establish infection. We report that the intracellular bacterium Legionella pneumophila secretes the toxin SidI (substrate of icm/dot transporter I), which possesses a transfer RNA (tRNA)-like shape and functions as a mannosyl transferase. The 3.1 Å cryo-EM structure of SidI reveals an N-terminal domain that exhibits a characteristic ‘inverted L-shape’ and charge distribution that is present in two other known protein mimics of tRNAs, the bacterial elongation factor EF-G and the mammalian release factor eRF1. In addition, we show that SidI’s C-terminal domain adopts a glycosyl transferase B fold similar to a mannosyl transferase. This molecular coupling of the protein’s fold and enzymatic function allows SidI to bind and glycosylate components of the host translation apparatus, including the ribosome, resulting in a robust block of protein synthesis that is comparable in potency to ricin, one of the most powerful toxins known. Additionally, we find that translational pausing activated by SidI elicits a stress response signature reminiscent of the ribotoxic stress response that 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. Thus, using Legionella and its effectors as tools, we have unravelled the role of a ribosome-to-nuclear signalling pathway that regulates cell fate.Competing Interest StatementP.W. is an inventor on U.S. Patent 9708247 held by the Regents of the University of California that describes ISRIB and its analogues. Rights to the invention have been licensed by UCSF to Calico. The N.J.K. laboratory has received research support from Vir Biotechnology and F. Hoffmann-La Roche. N.J.K. has consulting agreements with the Icahn School of Medicine at Mount Sinai, New York, Maze Therapeutics, and Interline Therapeutics, is a shareholder of Tenaya Therapeutics, Maze Therapeutics and Interline Therapeutics, and is financially compensated by GEn1E Lifesciences, Inc. and Twist Bioscience Corporation. D.L.S. has a consulting agreement with Maze Therapeutics. All other authors declare no competing interests. ER -