Leaky membrane fusion: an ambivalent effect induced by antimicrobial polycations

Area of Science:

• Biophysics
• Membrane Biology
• Antimicrobial Research

Background:

• Antimicrobial peptides (AMPs) and synthetic mimics show promise as antibiotic alternatives.
• These compounds can perturb cell membranes, leading to permeabilization and vesicle aggregation in model systems.
• Apparent leakage in model studies may arise from unintended vesicle aggregation or fusion, complicating interpretation.

Purpose of the Study:

• To investigate the interactions between a polycation and negatively charged vesicles (phosphatidylethanolamine/phosphatidylglycerol).
• To differentiate true membrane permeabilization from artifactual leakage caused by vesicle aggregation and fusion.
• To assess the biological relevance and potential applications of observed membrane effects.

Main Methods:

• Utilized biophysical methods to study polycation-vesicle interactions.
• Employed PEGylation to prevent vesicle-vesicle contact and differentiate fusion from permeabilization.
• Monitored vesicle leakage using calcein fluorescence lifetime measurements.

Main Results:

• Observed lipid exchange during vesicle aggregation at low polycation concentrations.
• Identified "leaky fusion" occurring upon vesicle charge neutralization, leading to both fusion and leakage.
• PEGylation inhibited both fusion and leakage, confirming the role of membrane contact.
• Leakage increased with the likelihood of vesicle-vesicle contacts.

Conclusions:

• Leaky fusion is a potential artifact in model studies of membrane-active polycations that can be mistaken for direct permeabilization.
• Distinguishing leaky fusion from other mechanisms is critical for accurate assessment of antimicrobial activity, particularly regarding relevance to bacteria versus fungi.
• Leaky fusion may have implications for drug delivery, such as enhancing endosomal escape.