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Conference papers

Structure of a VirB8-like protein, one of the main components of the Type IV secretion system involved in horizontal gene transfer between bacteria

Abstract : Context: Antimicrobial resistance has emerged as a major threat to public health since the 2000s [1]. In Gram+ bacteria, integrative and conjugative elements (ICE) are one of the most common means for the transfer of virulence and antibiotic resistance genes [2]. These genome-integrated sequences are excised from the donor cell, duplicated and sent to the recipient cell through a conjugation pore. Then they both reintegrate their respective cell genome. If the conditions are met, the recipient cell is able to repeat the same process [2]. It is proposed that all the genes necessary for the mechanism are included in the transferred and integrated sequence [2]. One of the large protein complexes responsible for this cell-to-cell transfer is called T4SS (Type IV Secretion Systems). When compared to similar transfer systems in Gram-bacteria, all reveal proteins that support 1) the replication and transfer of the conjugative element, 2) the assembly of a transfer transmembrane macro-complex, 3) various enzymatic activities such as ATPases or peptidoglycan hydrolase [3]. Contrary to Gram-, no overall structure of a Gram+ transmembrane complex is available from CryoEM experiments. The differences in cell-wall organization of both Gram types make the transposition of knowledge from one system to the other uncertain. Results: By NMR and X-Ray crystallography, we study protein products of the integrative and conjugative element ICESt3 from the Gram+ Streptococcus thermophilus, named OrfA to OrfM. Among them, OrfG is a key component of the macromolecular assembly that constitutes the secretion pore through the cell wall. Here we present the structure of two domains from its soluble part, which reveal the same folds as their VirB8 equivalents in various Gram-bacteria. Conclusion: Despite showing VirB8-like fold, the structure of OrfG is closer to that of two other Gram+ proteins, TcpC and TraM, with very low sequence identity [4]. The observation of trimeric assemblies in all three cases makes it a likely characteristic of this group, in contrast to what is observed in Gram. The reality of this assembly remains to be evaluated in vivo, especially considering the need for a transmembrane pore that would allow cell-to-cell transfer of genes. Waiting for CryoEM data on the whole secretion pore, the structures of its isolated proteins will help in understanding the role of each component in this supramolecular assembly, in order to build the first model of a Gram+ type-IV secretion system. [1] Ventola C. L. P. T., 2015, 40(4): 277. [2] Johnson C. M. & Grossman A. D. Annu Rev Genet, 2015, 49: 577-601. [3] Goessweiner-Mohr N. et al. Microbiol. Spectr., 2014, 2(4): 0004--2013. [4] Cappele J. et al. Front. Mol. Biosci. 2021, 8:642606. doi: 10.3389/fmolb.2021.642606.
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Submitted on : Wednesday, February 16, 2022 - 3:12:55 PM
Last modification on : Friday, April 22, 2022 - 10:48:12 AM


  • HAL Id : hal-03576846, version 1


Julien Cappele, Badreddine Douzi, Abbas Mohamad Ali, Nathalie Leblond-Bourget, Sandrine Mathiot, et al.. Structure of a VirB8-like protein, one of the main components of the Type IV secretion system involved in horizontal gene transfer between bacteria. SFB-GEM Meeting 2021 - Biophysics of membranes and beyond., Sep 2021, Online, France. ⟨hal-03576846⟩



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