C-terminal (CT) domain of the contact-dependent growth inhibition (CDI) system (CdiA-CT) protein CdiA of Enterobacter cloacae, and similar proteins
CDI toxins are expressed by gram-negative bacteria as part of a mechanism to inhibit the growth of neighboring cells. CdiA secretion is dependent on the outer membrane protein CdiB. Upon binding to a receptor on the surface of target bacteria, the CDI toxin is delivered via the C-terminal domain. A wide variety of C-terminal toxin domains appear to exist; this particular model contains the C-terminal (CT) domain of Enterobacter cloacae CdiA and similar domains. This CdiA-CT toxin has structural homology to the C-terminal nuclease domain of colicin E3, which cleaves 16S ribosomal RNA to disrupt protein synthesis, and has been shown to use the same nuclease activity to inhibit bacterial growth. The CdiA-CT toxin is specifically neutralized by cognate immunity protein CdiI to protect the toxin-producing cell from autoinhibition. Despite carrying equivalent toxin domains, the corresponding immunity proteins for CdiA-CT and colicin E3 are unrelated in sequence, structure, and toxin-binding site, thus showing diversity among 16S rRNase toxins.
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