Selective Membrane Disruption Mechanism of an Antibacterial γ-Aapeptide Defined by EPR Spectroscopy

Abstract

γ-AApeptides are a new class of antibacterial peptidomimetics that are not prone to antibiotic resistance and are highly resistant to protease degradation. How γ-AApeptides interact with bacterial membranes and alter lipid assembly and properties are unclear, but such information is essential in order to understand their antimicrobial activities. Using electron paramagnetic resonance (EPR) techniques, we characterized the membrane interaction and destabilizing activities of a lipo-cyclic-γ-AApeptide. The analyses revealed that the γ-AApeptide binding increases the membrane permeability of POPC/POPG liposomes, which mimics negatively-charged bacterial membranes. Moreover, the γ-AApeptide interacts strongly with POPC/POPG liposomes, thereby inhibiting membrane fluidity and reducing solvent accessibility around the lipid head group region. Furthermore, binding of the γ-AApeptide induces significant lipid-lateral-ordering and membrane thinning. In contrast, minimal membrane property changes were observed upon the γ-AApeptide binding for liposomes mimicking mammalian cell membranes, consisting of neutral lipids and cholesterol. Our findings suggest that the γ-AApeptide interact and disrupt bacterial membranes through a “carpet-like” mechanism. The results illustrated that the intrinsic features of γ-AApeptides are important for their ability to selectively disrupt bacterial membranes, the implications of which extend to developing new antibacterial biomaterials.