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Title: Investigating structural properties of lipid bilayers through the use of molecular rotors
Author: Dent, Michael
ISNI:       0000 0004 6421 0381
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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As the physical boundary separating the cell interior from the outside world, the plasma membrane is arguably one of the most important cellular organelles. Along with the proteins embedded within it, the plasma membrane plays a part in a number of vital roles including intercellular communication, cell motility and homeostasis. Despite this, comparatively little is known about the exact structure of the plasma membrane. The plasma membrane is a lipid bilayer that is widely believed to undergo transient phase separation into domains of different viscosities, which may be responsible for certain membrane properties. By using molecular rotors (organic fluorophores whose fluorescence properties depend on the viscosity of their surrounding environment) in conjunction with fluorescence lifetime imaging microscopy (FLIM), it is possible to generate a viscosity map of a heterogeneous biological system. In this thesis, we use molecular rotors to investigate the viscoelastic properties and phase behaviour of a range of lipid bilayer systems. We begin by using molecular rotors based on a boron-dipyrrin (BODIPY) core to investigate membrane viscosity within model systems, finding that different lipid phases display different viscosities, and visualising lipid phase separation within giant vesicles. We go on to use BODIPY rotors to image viscosity within the plasma membranes of live Escherichia coli bacteria at different temperatures, finding that they display a much higher degree of membrane ordering than previously observed in eukaryotic cells. Next we explore synthetic alternatives to the conventionally used BODIPY rotors in order to address their shortcomings, before using molecular rotors based on a thiophene moiety to determine the viscosity of the plasma membranes of live human cell lines. Our results from these studies suggest that phase-separation may indeed occur within the plasma membrane.
Supervisor: Kuimova, Marina ; Brooks, Nicholas ; Bull, James ; Krams, Rob Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral