A model membrane approach for interrogating membrane morphological responses induced by membrane-active peptides surfactants
Kim, Min Chul
Date of Issue2017-12-08
School of Materials Science and Engineering
Centre for Biomimetic Sensor Science
The cellular membrane is a complex, self-assembled biological structure that is responsible for numerous physiological functions and also serves to compartmentalize various cell organelles. There is great interest in understanding how membrane-active agents perturb cellular membranes from diverse origins, e.g., mammalian and bacterial, as well as other biological entities such as much smaller, enveloped viruses. This interest has directed countless efforts to attempt to mimic the complex nature of cellular membranes in order to create different types of model membrane platforms. In this thesis, the main objective is to examine the biophysical interactions between membrane-active agents such as amphipathic peptides, fatty acids, and monoglycerides, and model membrane platforms in order to distinguish the corresponding membrane morphological responses. The overall hypothesis is that probing membrane morphological responses induced in model lipid membrane platforms can distinguish the mechanisms of action of membrane-active peptides and monoglycerides, thereby revealing novel biophysical insights into molecular evolution and anti-infective applications. Within this scope, three main experimental studies were conducted that were aimed at developing more biologically relevant model platforms as well as investigating unexplored monoglyceride molecules of biological importance. In the first study, in order to create a defect-free supported lipid bilayer, an α-helical (AH) peptide derived from nonstructural protein (NS5A) of the hepatitis C virus, was employed to repair the still unruptured vesicles trapped in the initially formed bilayer after the vesicle fusion, revealing a correlation between vesicle size and rupture potency. For the second study, the preparation of giant unilamellar vesicles (GUVs) that include fractions of human liver microsome (HLM) extracts was conducted in order to study the interactions against AH peptide. Based on the experimental results obtained at different HLM fractions and peptide concentrations in a systematic fashion, it was identified that HLM-GUVs were more resistant to peptide-induced disruption in direct comparison with DOPC-GUVs, which are composed of wholly synthetic lipids. In the third study, the interaction between GUVs and glycerol monolaurate was explored for the first time. Depending on the aggregation state of glycerol monolaurate (monomeric versus micellar states), vesicle fission and fusion behaviors were observed in both simple and complex GUV compositions. This is the first example of a single molecule that can induce both vesicle fusion and fission, highlighting the potentially significant role of monoglycerides in evolutionary biology as a more advanced molecular structure going beyond the earliest, primitive cellular membranes composed of fatty acids. In summary, the findings in this thesis contribute to a fundamental understanding of how different classes of molecules – peptides, fatty acids, monoglycerides – induce membrane morphological responses in biologically relevant model membranes and offer insights into the roles in which these morphological responses play in therapeutic applications as well as molecular evolution.