| dc.description.abstract | Cell membranes function as physical barriers, as well as interactive interfaces, between the highly regulated and controlled environment inside the cell and the rapidly changing and potentially harmful environment outside the cell. The physical arrangement of lipids has a large contribution to the physical properties of the membrane, which in turn affect its interaction with external influences. This thesis aims to investigate the effects of two exogenous, membrane-active, biological substances on cell membranes and membrane models.
Epsilon toxin (Etx) is a potent cytolytic agent which acts by forming pores in a host cell membrane, causing cell lysis. The mechanism of action of pore-forming toxins can be divided into three stages (binding, oligomerisation, and pore-formation) the details of which are not well known for Etx. This project aims to characterise the interaction of Etx with lipid membranes by assessing toxicity of mutated Etx variants (Y42A, Y43A, and H162A) at each stage of action.
Chitosan is a polysaccharide with many unique applications involving cell membranes. It is known to affect the membrane but does not form pores, the interaction instead being thought to be associated with the physical state of the lipids within the membrane. This action was investigated by observing the changes to mammalian cell representative mixtures of lipid monolayers in a Langmuir trough, firstly by measuring surface pressure changes, then by measuring x-ray reflectivity and diffraction.
The results of Etx action on cell membranes have shed light on the complexity of binding mechanisms that Etx can employ in RBCs. We found that the H162A variant, previously thought to be non-toxic, became active at physiological temperature and we explain this through discussion of thermal fluctuations in the lipid environment. The observations of chitosan and lipid monolayers showed that it is strongly attracted to the inner leaflet lipid mixture, through electrostatic, H-bonding and hydrophobic interactions, disrupting lateral order and stiffening the monolayer. This could have medical implications in cases where chitosan is used as a medicine or as a drug delivery system to cells, where the strong attraction to the inner leaflet may cause chitosan to penetrate through the outer leaflet. | en_GB |
