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.