Identification and three‐dimensional structure of carnobacteriocin XY, a class IIb bacteriocin produced by Carnobacteria

In this study, we report that CbnX (33 residues) and CbnY (29 residues) comprise a class IIb (two‐component) bacteriocin in Carnobacteria. Individually, CbnX and CbnY are inactive, but together act synergistically to exert a narrow spectrum of activity. The structures of CbnX and CbnY in structure‐inducing conditions were determined and strongly resemble other class IIb bacteriocins (i.e., LcnG, PlnEF, PlnJK). CbnX has an extended, amphipathic α‐helix and a flexible C terminus. CbnY has two α‐helices (one hydrophobic, one amphipathic) connected by a short loop and a cationic C terminus. CbnX and CbnY do not appear to interact directly and likely require a membrane‐bound receptor to facilitate formation of the bacteriocin complex. This is the first class IIb bacteriocin reported for Carnobacteria.