Abstract
Many bacterial pathogens can enter various host cells and then survive intracellularly, transiently evade humoral immunity, and further disseminate to other cells and tissues. When bacteria enter host cells and replicate intracellularly, the host cells sense the invading bacteria as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) by way of various pattern recognition receptors. As a result, the host cells induce alarm signals that activate the innate immune system1. Therefore, bacteria must modulate host inflammatory signalling and dampen these alarm signals2,3,4. How pathogens do this after invading epithelial cells remains unclear, however. Here we show that OspI, a Shigella flexneri effector encoded by ORF169b on the large plasmid and delivered by the type ΙΙΙ secretion system, dampens acute inflammatory responses during bacterial invasion by suppressing the tumour-necrosis factor (TNF)-receptor-associated factor 6 (TRAF6)-mediated signalling pathway. OspI is a glutamine deamidase that selectively deamidates the glutamine residue at position 100 in UBC13 to a glutamic acid residue. Consequently, the E2 ubiquitin-conjugating activity required for TRAF6 activation is inhibited, allowing S. flexneri OspI to modulate the diacylglycerol–CBM (CARD–BCL10–MALT1) complex–TRAF6–nuclear-factor-κB signalling pathway. We determined the 2.0 Å crystal structure of OspI, which contains a putative cysteine–histidine–aspartic acid catalytic triad. A mutational analysis showed this catalytic triad to be essential for the deamidation of UBC13. Our results suggest that S. flexneri inhibits acute inflammatory responses in the initial stage of infection by targeting the UBC13–TRAF6 complex.
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Acknowledgements
We thank H. Fukuda for matrix-assisted laser desorption/ionization–time of flight (MALDI–TOF) analysis. We thank the members of the Sasakawa laboratory for their advice. We are grateful to R. Whittier for critical reading of the manuscript. Diffraction data were collected at the Osaka University beamline BL44XU at SPring-8. This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (23121525 (T.M.)), a Grant-in-Aid for Specially Promoted Research (23000012 (C.S.)), a Grant-in Aid for Young Scientists (A) (23689027 (M.K.)), several Grants-in-Aid for Young Scientists (B) (23790471 (M.O.), 23790472 (H.A.) and 22790403 (T.S.)), a Grant-in-Aid for Scientific Research (B) (23390102 (H.M.)), a Grant-in-Aid for Challenging Exploratory Research (23659220 (H.M.)), a Grant-in-Aid for Scientific Research on Priority Areas (18073003 (C.S.)) and the Japan Initiative for Global Research Network on Infectious Diseases (C.S.). Part of this work was supported by grants from the Naito Foundation (M.K. and H.M.), the Waksman Foundation of Japan (M.O.), the Yakult Bio-Science Foundation (M.O.), the Yakult Central Institute (C.S.) and The Hayashi Memorial Foundation for Female Natural Scientists (M.K.).
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T.S. and T.M. designed and performed the experiments. M.K., H.M., M.S., H.A., A.O., T. Kobayashi and M.O. assisted with the experiments. J.G., Y.S. and J.I.I. gave advice regarding the design of the experiments and provided TRAF6 materials. T. Koyama and S.N. made antibodies. A.O. made the ΔospI mutant. C.S. and T.M. wrote the paper.
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Atomic coordinates and structure factors for the OspI structure have been deposited in the PDB under ID 3B21.
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This file contains Supplementary Figures 1-15 and Supplementary Table 1. (PDF 16996 kb)
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Sanada, T., Kim, M., Mimuro, H. et al. The Shigella flexneri effector OspI deamidates UBC13 to dampen the inflammatory response. Nature 483, 623–626 (2012). https://doi.org/10.1038/nature10894
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DOI: https://doi.org/10.1038/nature10894
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