Contact-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) which bind CdiA-CT domains and neutralize their toxic activity to protect against self-inhibition. CdiI immunity proteins are also variable and only neutralize their cognate CdiA-CT toxins. Structure analysis of CdiI from Escherichia coli 536 (EC536) shows that is composed of a single domain and that it blocks the interaction with substrate, strongly suggesting that the immunity protein occludes the nuclease active site [1].

1: 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;113:9792-9797. PMID:27531961