Investigation of Interaction of Antimicrobial Peptides with Lipid Monolayers

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Abstract

With the increasing occurrence of multi-drug resistant bacteria, which has put the health of modern society under serious threat, novel anti-infective agents are needed in order to tackle this crisis. Antimicrobial peptides are a class of molecules which, due to their non-selective interactions via disrupting or permeabilizing bacterial membranes, have big potential in being developed as such novel therapeutics. An important step in understanding the antimicrobial mechanism of action of antimicrobial peptides is to understand the binding and interaction behaviour of the peptides with the membranes and how the membrane composition and properties affect their action mechanisms. Thus, motivated by this fact, the scope of this thesis is to study how a de novo designed antimicrobial peptide with the sequence G(IIKK)4-I-NH2 (denoted G4) interacts with model lipid monolayers mimicking the cell membranes of hosts (mammals) and those of pathogens (Gram-positive and Gram-negative bacteria). This was achieved by combining surface pressure measurements, Brewster angle microscopy (BAM), external reflection Fourier transform infrared (ER-FTIR) spectroscopy and neutron reflectivity (NR). In the course of this thesis model lipid monolayers of one, two and three components were created. Then it was assessed how the charge, acyl chain saturation and lateral packing of the monolayers affect the binding of the antimicrobial peptide G4. Comparative studies of peptide-lipid interactions using natural peptides such as LL-37 and the designed G4 peptide have revealed that G4 could permeabilize the membrane via a pore formation mechanism. Moreover, the monolayer measurements agree well with the minimum inhibitory concentrations and haemolytic activities of these peptides. In conclusion, this thesis has demonstrated how model lipid monolayers and the combined approach of several surface sensitive techniques could help in gaining important information regarding the selective interactions of antimicrobial peptides. As a result, a number of follow-up studies have been planned in the future to explore this area and to help unravel the mechanism of action of designed peptides such as G4. Moreover, the gained knowledge can be used to develop shorter peptides with greater antimicrobial activity and less cytotoxicity to mammalian host cells.

Keyword(s)

antimicrobial peptide; lipid monolayer; neutron reflectometry

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