Interaction of antimicrobial peptide magainin 2 with gangliosides as a target for human cell binding

Understanding how antimicrobial peptides (AMPs) interact with human cells is important to the development of antimicrobial agents as well as anticancer drugs. However, little is known about the mechanisms by which AMPs bind to cells and exert cytotoxicity. Negatively charged gangliosides on the cell surface are a potential target for cell binding. In this study, we investigated the interaction of F5W-magainin 2 (MG) with gangliosides in detail. MG was colocalized with gangliosides on HeLa cells, indicating that gangliosides act as a receptor for MG. MG also bound to gangliosides in model membranes. The affinity increased with the number of negatively charged sialic acid residues. Physicochemical studies revealed that MG interacts with the monosialoganglioside GM1 differently from the typical bacterial anionic phospholipid phosphatidylglycerol. MG bound to GM1 more strongly than to phosphatidylglycerol, and the binding isotherm for GM1 could be analyzed by the Langmuir equation assuming charge neutralization. This is in contrast to the binding of AMPs to phosphatidylglycerol-containing bilayers, which has been described by the electrostatic attraction-surface partitioning model. Fluorescence resonance energy transfer experiments supported the clustering of GM1, but not phosphatidylglycerol, by MG. Quenching data suggested that MG is bound to the sugar region of GM1. The bound peptide assumed a helical structure and induced the leakage of calcein and the coupled flip-flop of lipids, indicating the peptide also forms a toroidal pore in GM1-containing vesicles. However, the membrane permeabilizing activity was weaker against GM1-containing membranes than phosphatidylglycerol-doped liposomes in accordance with the trapping of the peptide in the sugar region. These results shed light on AMP-human cell interaction.