5j43
From Proteopedia
CdiA-CT from uropathogenic Escherichia coli in complex with CysK
Structural highlights
FunctionCYSK_ECOLI (Microbial infection) In addition to its role in cysteine synthesis, stimulates the tRNase activity of CdiA-CT from E.coli strain 536 / UPEC; stimulation does not require O-acetylserine sulfhydrylase activity. CdiA is the 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 (experiments done in strains BW25113 and X90, both K12 derivatives). This protein is not required for CDI of strain EC93, whose toxin may function by forming inner cell membrane pores (PubMed:22333533). CysK stabilizes CdiA-CT, allowing it to bind tRNA substrate; neither CdiA-CT nor CysK bind tRNA alone in vitro (PubMed:27531961).[1] [2] Publication Abstract from PubMedContact-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[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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