Antimicrobial peptide pores in membranes detected by neutron in-plane scattering

Antimicrobial peptides isolated from the host defense systems of animals have been shown to exert their activity directly on the lipid bilayer of cell membranes, but the antimicrobial mechanisms are not clear, due chiefly to the difficulty of discerning the high-order structures formed by these peptides in membranes. Previously we have shown that these peptides insert into the membrane when their concentrations exceed a lipid-dependent critical value. With neutron in-plane scattering we now show that inserted alamethicin creates aqueous pores approximately greater than 18 A in diameter. The density of pores is consistent with the assumption that all of the alamethicin is involved in pore formation. Pores were not detected below the critical concentration. Thus concentration-dependent pore formation appears to be the molecular mechanism of antimicrobial action.