Type IV secretion (T4S) systems form the most common and versatile class of secretion systems in bacteria, capable of injecting both proteins and DNAs into host cells. T4S systems are typically composed of 12 components that form 2 major assemblies: the inner membrane complex embedded in the inner membrane and the core complex embedded in both the inner and outer membranes. Here we present the 3.3 Å-resolution cryo-electron microscopy model of the T4S system core complex from Xanthomonas citri, a phytopathogen that utilizes this system to kill bacterial competitors. An extensive mutational investigation was performed to probe the vast network of protein–protein interactions in this 1.13-MDa assembly. This structure expands our knowledge of the molecular details of T4S system organization, assembly and evolution.
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Density map is available at EMDB with accession code EMD-0089. Atomic model is available in Protein Data Bank with accession code 6GYB. NMR data are available at BMRB with accession number 27342. All other data supporting the findings of this study are available from the corresponding authors upon request.
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This work was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) grants 2011/07777-5 and 2017/17303-7 to C.S.F. and Wellcome Trust grant 098302 to G.W. G.G.S. and W.C. were recipients of FAPESP post-doctoral fellowship grants. D.P.S. and L.C.O. received post-doctoral and PhD scholarships, respectively, from the Conselho Nacional de Pesquisa e Desenvolvimento (CNPq). We thank the members of the Farah and Waksman laboratories for fruitful discussions. We thank A. Bruni-Cardoso for fluorescence microscope access. We thank LNNano/CNPEM for the access to the cryo-EM facility, proposals TEM-19470 and TEM-20247. We thank Diamond for access to and support of the Cryo-EM facilities at the UK national Electron Bio-Imaging Centre (eBIC), proposal EM14704, funded by the Wellcome Trust, MRC and BBSRC. We thank N. Lukoyanova for the use of the ISMB Polara microscope.
The authors declare no competing interests.
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Sgro, G.G., Costa, T.R.D., Cenens, W. et al. Cryo-EM structure of the bacteria-killing type IV secretion system core complex from Xanthomonas citri. Nat Microbiol 3, 1429–1440 (2018). https://doi.org/10.1038/s41564-018-0262-z
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