Interaction of the Antimicrobial Peptide Aurein 1.2 and Charged Lipid Bilayer

Durgesh K. Rai,Shuo Qian

doi:10.1038/s41598-017-03795-6

Abstract

Aurein 1.2 is a potent antimicrobial peptide secreted by frog Litoria aurea. As a short membrane-active peptide with only 13 amino acids in sequence, it has been found to be residing on the surface of lipid bilayer and permeabilizing bacterial membranes at high concentration. However, the detail at the molecular level is largely unknown. In this study, we investigated the action of Aurein 1.2 in charged lipid bilayers composed of DMPC/DMPG. Oriented Circular Dichroism results showed that the peptide was on the surface of lipid bilayer regardless of the charged lipid ratio. Only at a very high peptide-to-lipid ratio (~1/10), the peptide became perpendicular to the bilayer, however no pore was detected by neutron in-plane scattering. To further understand how it interacted with charged lipid bilayers, we employed Small Angle Neutron Scattering to probe lipid distribution across bilayer leaflets in lipid vesicles. The results showed that Aurein 1.2 interacted strongly with negatively charged DMPG, causing strong asymmetry in lipid bilayer. At high concentration, while the vesicles were intact, we found additional structure feature on the bilayer. Our study provides a glimpse into how Aurein 1.2 disturbs anionic lipid-containing membranes without pore formation.

Highlights

Aurein peptides are a large family of peptides discovered in the skin secretions of Litoria genus of Australian frogs with various degree of antimicrobial activity
What is absent are intermediate states transiting from S state to I state as the peptide-to-lipid ratio (P/L) increases
Many well-studied antimicrobial peptides such as alamethicin, melittin, etc. have been observed to undergo a gradual transition from S state to I state as peptide concentration increases[17, 19]

Summary

Introduction

Aurein peptides are a large family of peptides discovered in the skin secretions of Litoria genus of Australian frogs with various degree of antimicrobial activity. Through the action on membranes like many other antimicrobial peptides, it inhibits both intact Gram-negative and Gram-positive bacteria[3] It shows a moderate anti-cancer activity on 52 out of the 54 cancer cells in the NCI testing program, at the concentrations that can kill bacterial and cancer cells without harming mammalian cells[2]. With SANS, we’ve found that some of the well-studied membrane-active peptides such as alamthicin and melittin are capable of modifying charged lipids or cholesterol distribution in lipid bilayers even at the low concentrations that are below their pore formation concentrations[20,21,22]. Our results suggest that aurein binding on the bilayer causes a strong redistribution of the charged lipid in the outer leaflet, and the formation of lipid-aurein complex Such rearrangement makes membrane fragile and permeable, prone to further defect that is deadly. Such actions of aurein could well damage the membrane integrity without forming any transmembrane pore

Methods

Results

Conclusion