Neutral peptides allow aggregation of cationic peptides in antimicrobial secretory fluids

Antimicrobial peptides (AMPs) are seen as a promising alternative to conventional antibiotics, yet their mechanism of action is not fully understood. We recently proposed that AMPs do not act as isolated monomers but instead aggregate into nano-sized clusters before targeting the membrane. However, cationic peptides may struggle to form clusters large enough to achieve effective membrane disruption alone, suggesting the involvement of a co-actor in this process. Here, we tackle this issue through both in silico and in vitro studies of mono- and bicomponent solutions comprising two newly identified peptides, one charged and the other neutral, before the interaction with the target membrane. We observe that while the charged peptides alone do not form clusters of noticeable size, in the mixture with the neutral peptides they coalesce into layered aggregates with a hydrophobic core of the neutral moiety and the charged monomers exposed to the surrounding solvent. The size of these mixed charged/neutral peptides aggregates is smaller than the ones in the neutral monocomponent solution due to the counteraction of electrostatic repulsion to the hydrophobic effect. We regard the structures thus formed as an ideal transport system - locking hydrophobic uncharged residues in the cluster core prevents interaction with eukaryotic membranes, while solvent-exposed charged residues facilitate electrostatic interaction with bacterial surfaces.