Structure function relationship of inducer peptide pheromones involved in bacteriocin production in Carnobacterium maltaromaticum and Enterococcus faecium.

The production of several bacteriocins in lactic acid bacteria is regulated by inducer peptide pheromones that specifically interact with their cognate bacterial receptor. These peptide pheromones are between 19 and 27 aa long and contain a conserved (V/I)-X-X-X-F sequence followed by positively charged residues in the C-terminal domain. CbaX and EntF are peptide pheromones that share similarity and are involved in the production of carnobacteriocin A in Carnobacterium maltaromaticum LV17A and enterocins A and B in Enterococcus faecium CTC492, respectively. CbaX, EntF and two hybrids, CbaX::EntF and EntF::CbaX, were tested for pheromone activity in LV17A and CTC492. EntF and EntF::CbaX only induced bacteriocin production in CTC492, whereas CbaX and CbaX::EntF induced carnobacteriocin A production in LV17A and, at high concentrations, also cross-induced enterocin production in CTC492. Various peptide fragments of CbaX and EntF were made for further structure-function analysis. The C-terminal fragments, but not the N-terminal fragments, were able to effect bacteriocin induction. The 10-mer EntF(16-25), derived from the C-terminal domain of EntF, showed pheromone activity in LV17A. In contrast, the C-terminal 9-mer of CbaX, CbaX(16-24), inhibited pheromone activity in both LV17A and CTC492. EntF(16-25) and CbaX(16-24) differ by two amino acids. Changing either one of these abolished pheromone activity as well as the ability to inhibit pheromone activity. These results indicate that the C-terminal domain of these peptide pheromones interacts relatively non-specifically with the receptor, and that induction is greatly facilitated by the N-terminal domain that recognizes specifically its cognate receptor.