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. Structure analysis of CdiA-CT shows that it adopts the same fold (with two beta-sheets forming an overall kidney shape) as angiogenin and other RNase A paralogs, but the toxin does not share sequence similarity with these nucleases and lacks the characteristic disulfide bonds of the superfamily. Furthermore, structural comparison analysis identified human angiogenin, Rana pipiens protein P-30 (onconase) and mouse pancreatic ribonuclease (RNase 1) as the closest structural homologs of CdiA-CT [1].

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