Contact-dependent growth inhibition (CDI) is an important mechanism of inter-bacterial competition found in many Gram-negative pathogens. CDI+ cells express cell-surface CdiA proteins that bind neighboring bacteria and deliver C-terminal toxin domains (CdiA-CT) to inhibit target-cell growth. CDI+ bacteria also produce CdiI immunity proteins, which specifically neutralize cognate CdiA-CT toxins to prevent self-inhibition. Structure analysis of CdiI immunity protein from Yersinia kristensenii shows that it is composed of eight alpha-helices packed together to form a nearly spherical structure with weak structural homology to a putative TetR family transcriptional repressor. The CdiI protein fits into the curved cavity of the CdiA-CTYkris toxin domain where it most likely neutralizes toxin activity by blocking access to RNA substrates [1]. This domain is mostly found in gammaproteobacteria.

1: The CDI toxin of Yersinia kristensenii is a novel bacterial member of the RNase A superfamily. Batot G, Michalska K, Ekberg G, Irimpan EM, Joachimiak G, Jedrzejczak R, Babnigg G, Hayes CS, Joachimiak A, Goulding CW; Nucleic Acids Res. 2017;45:5013-5025. PMID:28398546