5j4a | pdb_00005j4a
CdiA-CT toxin from Burkholderia pseudomallei E479 in complex with cognate CdiI immunity protein
Structural highlights
Function[CDIA9_BURPE] 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. The C-terminal 160 residues (CT domain) acts as a general tRNA nuclease, and inhibits growth in E.coli. Cleaves specifically within the T-loop of E.coli tRNA2(Arg). Toxic activity is neutralized by coexpression of the cognate immunity protein CdiI in E.coli, but not by non-cognate immunity proteins from other strains of B.pseudomallei.[1] Publication Abstract from PubMedContact-dependent growth inhibition (CDI) is a wide-spread mechanism of inter-bacterial competition. CDI+ bacteria deploy large CdiA effector proteins, which carry variable C-terminal toxin domains (CdiA-CT). CDI+ cells also produce CdiI immunity proteins that specifically neutralize cognate CdiA-CT toxins to prevent auto-inhibition. Here, we present the crystal structure of the CdiA-CT/CdiIE479 toxin/immunity protein complex from Burkholderia pseudomallei isolate E479. The CdiA-CTE479 tRNase domain contains a core alpha/beta-fold that is characteristic of PD-(D/E)XK superfamily nucleases. Unexpectedly, the closest structural homolog of CdiA-CTE479 is another CDI toxin domain from B. pseudomallei 1026b. Though unrelated in sequence, the two B. pseudomallei nuclease domains share similar folds and active-site architectures. By contrast, the CdiIE479 and CdiI1026b immunity proteins share no significant sequence or structural homology. CdiA-CTE479 and CdiA-CT1026b are both tRNases, however the cleavage positions are different for each nuclease. We used a molecular docking approach to model each toxin bound to tRNA substrate. The resulting models fit into electron density envelopes generated by small-angle X-ray scattering analysis of stable complexes of tRNA bound to catalytically inactive toxin domains. CdiA-CTE479 is the third CDI toxin with structural homology to the PD-(D/E)XK superfamily. PD-(D/E)XK nucleases are characterized by highly variable sequences and active-site plasticity. CDI systems exploit this structural flexibility to generate toxin diversity. These findings raise the possibility that many other uncharacterized CDI toxins may also belong to the PD-(D/E)XK superfamily. Functional Diversity of Cytotoxic tRNase/immunity Protein Complexes from Burkholderia pseudomallei.,Johnson PM, Gucinski GC, Garza-Sanchez F, Wong T, Hung LW, Hayes CS, Goulding CW J Biol Chem. 2016 Jul 20. pii: jbc.M116.736074. PMID:27445337[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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