Membrane-Binding Properties of the Antimicrobial Peptide Maximin 3

Abstract

Antimicrobial peptides (AMPs) are part of the innate immune system of most organisms, where they protect the organism from a variety of microbial agents. Research is ongoing to utilize AMPs and their derivatives for medicinal purposes, such as antibiotics that are less likely to induce antibiotic resistance in bacteria. This work focuses on the AMP Maximin 3, which is derived from the skin secretions of the toad Bombina maxima. Maximin 3 is a 27 amino acid cationic peptide that has strong activity against a variety of bacterial, fungal, and viral microbes and is thought to cause toxicity by interaction with the plasma membrane, though this interaction has not previously been observed. However, Maximin 3 is also toxic to mammalian cells and cannot be used therapeutically. The goal of this work is to characterize the membrane-binding of Maximin 3 with the ultimate goal of redesigning its sequence to increase selectivity for microbial membranes.This work examines four aspects of Maximin 3's interaction with membranes. First, fluorescence anisotropy was used to quantify the binding of Maximin 3 to model lipid membranes that mimic the composition of microbial or mammalian membranes. Maximin 3 was also observed binding to E. coli using fluorescence microscopy. Second, Forster resonance energy transfer was used to examine the structural changes that Maximin 3 undergoes upon membrane binding and to probe for structural differences between Maximin 3 bound to bacterial and mammalian model membranes. Third, fluorescence-based vesicle leakage assays were used to directly monitor membrane disruption caused by Maximin 3. And fourth, predicted structures of Maximin 3 and other Maximin peptides bound to membranes were prepared using Rosetta. Our results provide a comprehensive picture of Maximin 3 membrane interactions and suggest sequence modifications that may increase selectivity of the peptide.