MECHANISM OF ACTION OF THE ANTIMICROBIAL PEPTIDE BUFORIN-II - BUFORIN-II KILLS MICROORGANISMS BY PENETRATING THE CELL-MEMBRANE AND INHIBITING CELLULAR FUNCTIONS

The mechanism of action of buforin II, which is a 21-amino acid peptid e with a potent antimicrobial activity against a broad range of microo rganisms, was studied using fluorescein isothiocyanate (FITC)-labeled buforin II and a gel-retardation experiment. Its mechanism of action w as compared with that of the well-characterized magainin 2, which has a pore-forming activity on the cell membrane. Buforin II billed Escher ichia coli without lysing the cell membrane even at 5 times minimal in hibitory concentration (MIG) at which buforin II reduced the viable ce ll numbers by 6 orders of magnitude. However, magainin 2 lysed the cel l to death under the same condition. FITC-labeled buforin II was found to penetrate the cell membrane and accumulate inside E. coli even bel ow its MIC, whereas FITC-labeled magainin 2 remained outside or on the cell wall even at its MIC. The gel-retardation experiment showed that buforin II bound to DNA and RNA of the cells over 20 times strongly t han magainin 2. All these results indicate that buforin II inhibits th e cellular functions by binding to DNA and RNA of cells after penetrat ing the cell membranes, resulting in the rapid cell death, which is qu ite different from that of magainin 2 even though they are structurall y similar: a linear amphipathic alpha-helical peptide. (C) 1998 Academ ic Press.