LACTOCOCCIN-G IS A POTASSIUM ION-CONDUCTING, 2-COMPONENT BACTERIOCIN

Lactococcin G is a novel lactococcal bacteriocin whose activity depend s on the complementary action of two peptides, termed alpha and beta. Peptide synthesis of the alpha and beta peptides yielded biologically active lactococcin G, which was used in mode-of-action studies on sens itive cells of Lactococcus lactis. Approximately equivalent amounts of both peptides were required for optimal bactericidal effect. No effec t was observed with either the alpha or beta peptide in the absence of the complementary peptide. The combination of alpha and beta peptides (lactococcin G) dissipates the membrane potential (Delta psi), and as a consequence cells release alpha-aminoisobutyrate, a nonmetabolizabl e alanine analog that is accumulated through a proton motive-force dep endent mechanism. In addition, the cellular ATP level is dramatically reduced, which results in a drastic decrease of the ATP-driven glutama te uptake. Lactococcin G does not form a proton-Conducting pore, as it has no effect on the transmembrane pH gradient. Dissipation of the me mbrane potential by uncouplers causes a slow release of potassium (rub idium) ions. However, rapid release of potassium was observed in the p resence of lactococcin G. These data suggest that the bactericidal eff ect of lactococcin G is due to the formation of potassium-selective ch annels by the alpha and beta peptides in the target bacterial membrane .