Membrane-mimicking entities induce structuring of the two-peptide bacteriocins plantaricin E/F and plantaricin J/K

Lactobacillus plantarum C11 produces plantaricin E/F (PlnE/F) and plantaric in J/K; (PlnJ/K), two bacteriocins whose activity depends on the complement ary action of two peptides (PlnE and PlnF; PlnJ and PlnK). Three of the ind ividual Pln peptides possess some antimicrobial activity, but the highest b arteriocin activity is obtained by combining complementary peptides in abou t a one-to-one ratio. Circular dichroism was used to study the structure of the Pln peptides under various conditions, All four peptides were unstruct ured under aqueous conditions but adopted a partly alpha-helical structure in the presence of trifluoroethanol, micelles of dodecylphosphocholine, and negatively charged dioleoylphosphoglycerol (DOPG) liposomes, Far less stru cture was induced by zwitterionic dioleoylglycerophosphocholine liposomes, indicating that a net negative charge on the phospholipid bilayer is import ant for a structure-inducing interaction between (positively charged) Pln p eptides and a membrane. The structuring of complementary peptides was consi derably enhanced when both (PlnE and PlnF or PlnJ and PlnK) were added simu ltaneously to DOPG liposomes. Such additional structuring was not observed in experiments with trifluoroethanol or dodecylphosphocholine, indicating t hat the apparent structure-inducing interaction between complementary Pin p eptides requires the presence of a phospholipid bilayer, The amino acid seq uences of the Pln peptides are such that the alpha-helical structures adopt ed upon interaction with the membrane and each other are amphiphilic in nat ure, thus enabling membrane interactions.