The family of bacterial SidE enzymes catalyses phosphoribosyl-linked serine ubiquitination and promotes infectivity of Legionella pneumophila, a pathogenic bacteria that causes Legionnaires’ disease1–3. SidE enzymes share the genetic locus with the Legionella effector SidJ that spatiotemporally opposes the toxicity of these enzymes in yeast and mammalian cells, through a mechanism that is currently unknown4–6. Deletion of SidJ leads to a substantial defect in the growth of Legionella in both its natural hosts (amoebae) and in mouse macrophages4,5. Here we demonstrate that SidJ is a glutamylase that modifies the catalytic glutamate in the mono-ADP ribosyl transferase domain of the SdeA, thus blocking the ubiquitin ligase activity of SdeA. The glutamylation activity of SidJ requires interaction with the eukaryotic-specific co-factor calmodulin, and can be regulated by intracellular changes in Ca2+ concentrations. The cryo-electron microscopy structure of SidJ in complex with human apo-calmodulin revealed the architecture of this heterodimeric glutamylase. We show that, in cells infected with L. pneumophila, SidJ mediates the glutamylation of SidE enzymes on the surface of vacuoles that contain Legionella. We used quantitative proteomics to uncover multiple host proteins as putative targets of SidJ-mediated glutamylation. Our study reveals the mechanism by which SidE ligases are inhibited by a SidJ–calmodulin glutamylase, and opens avenues for exploring an understudied protein modification (glutamylation) in eukaryotes.
Bibliographical noteFunding Information:
Acknowledgements We thank J. Vogel for the ΔsidJ Legionella strain; Z.-Q. Luo for SidJ proteins purified from Legionella, and for providing ΔsidE and wild-type Legionella strains; S. Rodriguez and S. Gharbi for technical assistance; Y. Liu for help with deubiquitination assays; D. Höller, H. Marei and K. Koch for critical comments on the manuscript; and S. Knapp and V. Doetsch for discussion and advice. This work was supported by the DFG-funded Collaborative Research Centre on Selective Autophagy (SFB 1177), by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 742720), by the DFG-funded Cluster of Excellence ‘Macromolecular Complexes’ (EXC115) and by the DFG-funded SPP 1580 program ‘Intracellular Compartments as Places of Pathogen-Host-Interactions’ (to I.D.).
© 2019, The Author(s), under exclusive licence to Springer Nature Limited.
All Science Journal Classification (ASJC) codes