5i4r
Contact-dependent inhibition system from Escherichia coli NC101 - ternary CdiA/CdiI/EF-Tu complex (trypsin-modified)
Structural highlights
FunctionCDIA_ECONC 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 about 10,0000-fold for this system). CdiA toxicity is neutralized by its cognate immunity protein CdiI-NC101, but not by CdiI from other bacteria (PubMed:26305955, PubMed:28973472). The C-terminal domain (CT) cleaves tRNA endonucleolytically at the 5' side of guanine discriminator nucleotide sites (removes the last 4 nucleotides of the tRNA acceptor arm when the first nucleotide to be removed is G) (PubMed:28973472). Requires EF-Ts (tsf) for toxic function of the CT domain in vivo (PubMed:28223500). In vitro the CT tRNase activity requires both EF-Tu (tufA) and EF-Ts. EF-Ts probably increases steady-state GTP-EF-Tu-aa-tRNA substrate levels. The CT domain is thought to remodel this same complex to displace the 3'-end of the aa-tRNA and allow it to enter into the toxin active site (PubMed:28973472). The CT domain gains access to the cytoplasm of target cells by using integral inner membrane protein PTS system glucose-specific EIICB component (ptsG) (PubMed:26305955).[1] [2] [3] The CdiA protein is thought to be exported from the cell through the central lumen of CdiB, the other half of its two-partner system (TPS). The TPS domain probably remains associated with CdiB while the FHA-1 domain forms an extended filament with the receptor-binding domain (RBD) at its extremity; in the secretion arrested state the C-terminus of the RBD and YP domains form a hairpin-like structure as the FHA-2, PT and CT domains are periplasmic. The YP domain is probably responsible for this arrest at the point where it re-enters the host cell periplasm. Upon binding to a target cell outer membrane receptor a signal is transmitted to activate secretion. The filament elongates slightly, the rest of CdiA is secreted and the FHA-2 domain becomes stably associated with the target cell's outer membrane where it facilitates entry of the toxic CT domain into the target cell periplasm. From there the toxic CT domain is cleaved and gains access to the target cell cytoplasm via an inner membrane protein (PtsG for this CDI).[4] Publication Abstract from PubMedContact-dependent growth inhibition (CDI) is a mechanism of inter-cellular competition in which Gram-negative bacteria exchange polymorphic toxins using type V secretion systems. Here, we present structures of the CDI toxin from Escherichia coli NC101 in ternary complex with its cognate immunity protein and elongation factor Tu (EF-Tu). The toxin binds exclusively to domain 2 of EF-Tu, partially overlapping the site that interacts with the 3'-end of aminoacyl-tRNA (aa-tRNA). The toxin exerts a unique ribonuclease activity that cleaves the single-stranded 3'-end from tRNAs that contain guanine discriminator nucleotides. EF-Tu is required to support this tRNase activity in vitro, suggesting the toxin specifically cleaves substrate in the context of GTP.EF-Tu.aa-tRNA complexes. However, superimposition of the toxin domain onto previously solved GTP.EF-Tu.aa-tRNA structures reveals potential steric clashes with both aa-tRNA and the switch I region of EF-Tu. Further, the toxin induces conformational changes in EF-Tu, displacing a beta-hairpin loop that forms a critical salt-bridge contact with the 3'-terminal adenylate of aa-tRNA. Together, these observations suggest that the toxin remodels GTP.EF-Tu.aa-tRNA complexes to free the 3'-end of aa-tRNA for entry into the nuclease active site. Structure of a novel antibacterial toxin that exploits elongation factor Tu to cleave specific transfer RNAs.,Michalska K, Gucinski GC, Garza-Sanchez F, Johnson PM, Stols LM, Eschenfeldt WH, Babnigg G, Low DA, Goulding CW, Joachimiak A, Hayes CS Nucleic Acids Res. 2017 Sep 29;45(17):10306-10320. doi: 10.1093/nar/gkx700. PMID:28973472[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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