Contact-dependent growth inhibition (CDI) systems encode polymorphic toxin/immunity proteins that mediate competition between neighboring bacterial cells. CDI is mediated by the CdiB/CdiA family of two-partner secretion proteins. This domain represents the C-terminal of CdiA proteins (CdiA-CT), which contains the CDI toxin activity. The C-terminal nuclease domain forms a stable complex with its cognate immunity protein. It is also sufficient to inhibit growth when expressed in E. coli cells, consolidating the idea that they constitute the functional CDI toxin. The CdiA-CT C-terminal domains are structurally similar to type IIS restriction endonucleases suggesting that the toxins have metal-dependent DNase activity [1].

1: Structural basis of toxicity and immunity in contact-dependent growth inhibition (CDI) systems. Morse RP, Nikolakakis KC, Willett JL, Gerrick E, Low DA, Hayes CS, Goulding CW; Proc Natl Acad Sci U S A. 2012;109:21480-21485. PMID:23236156