Polyphenol-Mediated Peptide Assembly Modulates Melittin Toxicity: A Structure-Activity Strategy for Neutralizing the Interface Affinity of Pore-Forming Toxins to Cell Membranes.

Pore-forming agents can bind at the interface of and permeabilize cell membranes. Understanding and mitigating this mechanism is pragmatic for developing bionanomaterials and strategies against biologically active species that target the cell membrane. Herein, we explore the molecular interactions between melittin, a membrane-active pore-forming peptide from honeybee venom, and a series of structurally similar polyphenols. We sought to better understand the biophysical bases by which pore-forming toxins interact with cell membranes and to establish a materials-based strategy using small molecules to control peptide assembly and biotoxin activity at the membrane interface. Building on our previous discovery that epigallocatechin gallate reduces the membrane affinity of melittin by decreasing the extent of its solvent-exposed hydrophobicity and promoting its oligomerization into larger species that interact with a markedly lower affinity to cell membranes, we now establish a structure-activity relationship using five polyphenols. Combining biophysical measurements, assays using SH-SY5Y cells, and first-principles computational modeling, we show that the polyphenol-induced oligomerization of melittin correlates strongly with its reduced toxicity. Specifically, the degree of neutralization is predicted well by the binding affinity of the polyphenol to melittin and the resulting size of the supramolecular melittin-polyphenol complex, with larger assemblies exhibiting markedly diminished cytotoxicity due to the sequestration of the toxic, monomeric form of melittin. The stabilized melittin-polyphenol complexes also demonstrate differential resistances to dissociation using a chaotropic agent. These findings highlight the relevance of physicochemical properties in the ability of proteinaceous toxins to interface with cell membranes and suggest that modulating peptide assembly through molecular binding is a viable strategy to rationally assemble and control pore-forming toxins. This work offers a mechanistic framework for designing small molecule-stabilized biomaterials that can regulate interfaces, with relevance to nanomaterials and nanomedicine.