Interaction of cysteine-rich cationic antimicrobial peptides with intact bacteria and model membranes

Antimicrobial peptides are small proteins that exhibit a broad spectrum of antimicrobial activity. Their chemical structure allows them to interact (attach and insert) with membranes. The fine details about this interaction and their mode of action are not fully clarified yet. In order to better understand this mechanism, we have performed in situ atomic force microscopy studies using two types of nodule specific cysteine-rich NCR peptides on Escherichia coli bacteria and on natural purple membrane. On intact bacteria, both NCR247 and NCR335 caused increase in the surface roughness, indicating the damage of the bacterial cell envelope. In case of the tightly packed purple membrane, it is clear that the peptides prefer to disrupt the border of the disks indicating a strong lipid preference of the interaction. These results verify the concept that the first target of NCR peptides is probably the bacterial cell envelope, especially the lipid matrix.