| Structural highlights
Function
[CDIA_ECOL5] Toxic component of a toxin-immunity protein module, which functions as a cellular contact-dependent growth inhibition (CDI) system. CDI modules allow bacteria to communicate with and inhibit the growth of closely related neighboring bacteria in a contact-dependent fashion (target cell counts decrease 100- to 1000-fold). CdiA toxicity is neutralized by its cognate immunity protein CdiI, but not by CdiI from other bacteria (PubMed:23469034, PubMed:24889811). BamA on the target cells acts as a receptor for intact CdiA (PubMed:23469034). However isolated CdiA-CT is imported in an F-pilus-mediated fashion; CdiA-CT inhibits F-mediated conjugation, probably via its N-terminus (residues 3016-3097), although it is not clear if this is physiologically significant (PubMed:24889811). The C-terminal domain (CT) cleaves within tRNA anticodon loops (PubMed:22333533, PubMed:24889811); this activity is inhibited by cognate CdiI (PubMed:21085179, PubMed:22333533, PubMed:24889811). tRNase activity of CdiA-CT is stimulated by CysK, although the extreme C-terminus (residues 3098-3242) has tRNase activity in the absence of CysK. In vivo CDI toxicity requires CysK (PubMed:22333533, PubMed:24889811). Purified CdiA-CT (residues 3016-3242) inhibits E.coli cell growth when added to cultures alone or in complex with cognate CdiI, growth is inhibited when cognate CdiI is present within the cell but not when a CdiA-CT/CdiI complex is added extracellularly, suggesting CdiA-CT alone but not the CdiA-CT/CdiI complex is imported into the target cell (PubMed:24889811).[1] [2] [3] [4] [5]
Publication Abstract from PubMed
Contact-dependent growth inhibition (CDI) is a widespread mechanism of bacterial competition. CDI(+) bacteria deliver the toxic C-terminal region of contact-dependent inhibition A proteins (CdiA-CT) into neighboring target bacteria and produce CDI immunity proteins (CdiI) to protect against self-inhibition. The CdiA-CT(EC536) deployed by uropathogenic Escherichia coli 536 (EC536) is a bacterial toxin 28 (Ntox28) domain that only exhibits ribonuclease activity when bound to the cysteine biosynthetic enzyme O-acetylserine sulfhydrylase A (CysK). Here, we present crystal structures of the CysK/CdiA-CT(EC536) binary complex and the neutralized ternary complex of CysK/CdiA-CT/CdiI(EC536) CdiA-CT(EC536) inserts its C-terminal Gly-Tyr-Gly-Ile peptide tail into the active-site cleft of CysK to anchor the interaction. Remarkably, E. coli serine O-acetyltransferase uses a similar Gly-Asp-Gly-Ile motif to form the "cysteine synthase" complex with CysK. The cysteine synthase complex is found throughout bacteria, protozoa, and plants, indicating that CdiA-CT(EC536) exploits a highly conserved protein-protein interaction to promote its toxicity. CysK significantly increases CdiA-CT(EC536) thermostability and is required for toxin interaction with tRNA substrates. These observations suggest that CysK stabilizes the toxin fold, thereby organizing the nuclease active site for substrate recognition and catalysis. By contrast, Ntox28 domains from Gram-positive bacteria lack C-terminal Gly-Tyr-Gly-Ile motifs, suggesting that they do not interact with CysK. We show that the Ntox28 domain from Ruminococcus lactaris is significantly more thermostable than CdiA-CT(EC536), and its intrinsic tRNA-binding properties support CysK-independent nuclease activity. The striking differences between related Ntox28 domains suggest that CDI toxins may be under evolutionary pressure to maintain low global stability.
Unraveling the essential role of CysK in CDI toxin activation.,Johnson PM, Beck CM, Morse RP, Garza-Sanchez F, Low DA, Hayes CS, Goulding CW Proc Natl Acad Sci U S A. 2016 Aug 30;113(35):9792-7. doi:, 10.1073/pnas.1607112113. Epub 2016 Aug 16. PMID:27531961[6]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Aoki SK, Diner EJ, de Roodenbeke CT, Burgess BR, Poole SJ, Braaten BA, Jones AM, Webb JS, Hayes CS, Cotter PA, Low DA. A widespread family of polymorphic contact-dependent toxin delivery systems in bacteria. Nature. 2010 Nov 18;468(7322):439-42. doi: 10.1038/nature09490. PMID:21085179 doi:http://dx.doi.org/10.1038/nature09490
- ↑ Diner EJ, Beck CM, Webb JS, Low DA, Hayes CS. Identification of a target cell permissive factor required for contact-dependent growth inhibition (CDI). Genes Dev. 2012 Mar 1;26(5):515-25. doi: 10.1101/gad.182345.111. Epub 2012 Feb, 14. PMID:22333533 doi:http://dx.doi.org/10.1101/gad.182345.111
- ↑ Webb JS, Nikolakakis KC, Willett JL, Aoki SK, Hayes CS, Low DA. Delivery of CdiA nuclease toxins into target cells during contact-dependent growth inhibition. PLoS One. 2013;8(2):e57609. doi: 10.1371/journal.pone.0057609. Epub 2013 Feb 28. PMID:23469034 doi:http://dx.doi.org/10.1371/journal.pone.0057609
- ↑ Beck CM, Diner EJ, Kim JJ, Low DA, Hayes CS. The F pilus mediates a novel pathway of CDI toxin import. Mol Microbiol. 2014 Jul;93(2):276-90. doi: 10.1111/mmi.12658. Epub 2014 Jun 15. PMID:24889811 doi:http://dx.doi.org/10.1111/mmi.12658
- ↑ Ruhe ZC, Nguyen JY, Beck CM, Low DA, Hayes CS. The proton-motive force is required for translocation of CDI toxins across the inner membrane of target bacteria. Mol Microbiol. 2014 Oct;94(2):466-81. doi: 10.1111/mmi.12779. Epub 2014 Sep 17. PMID:25174572 doi:http://dx.doi.org/10.1111/mmi.12779
- ↑ Johnson PM, Beck CM, Morse RP, Garza-Sanchez F, Low DA, Hayes CS, Goulding CW. Unraveling the essential role of CysK in CDI toxin activation. Proc Natl Acad Sci U S A. 2016 Aug 30;113(35):9792-7. doi:, 10.1073/pnas.1607112113. Epub 2016 Aug 16. PMID:27531961 doi:http://dx.doi.org/10.1073/pnas.1607112113
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