tRNA nuclease CdiA

UniProtKB accession:  Q0T963

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UniProtKB description:  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). Uses heterotrimeric OmpC and OmpF as target cell outer membrane receptors; receptor function depends on polymorphisms in extracellular loops L4 and L5 of OmpC; interacts with itself and closely related bacteria but also with OmpC from E.cloacae ATCC 13047. Its ability to preferentially bind to 'self' receptors suggests it may also play a role in self-recognition and kin selection (PubMed:27723824). A bamA mutation that decreases its expression about 5-fold is partially resistant to this strain of CdiA, probably due to decreased outer membrane receptor protein assembly (PubMed:23469034). 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). Gains access to the cytoplasm of target cells by using integral inner membrane protein FtsH (PubMed:26305955). 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). CysK stabilizes CdiA-CT, allowing it to bind tRNA substrate; neither CdiA-CT nor CysK bind tRNA alone in vitro (PubMed:27531961). 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).