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Title: Novel fluorescence techniques to probe protein aggregation
Author: Taylor, Christopher George
ISNI:       0000 0001 0862 8511
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2018
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The self-assembly of amyloidogenic proteins to form cytotoxic species that give rise to brain deterioration underlies numerous neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases. Increasing evidence indicates that it is the rare, low-molecular-weight species (oligomers) rather than the more abundant high-molecular-weight fibrils of certain proteins that are the most cytotoxic in several neurodegenerative diseases. However, these species have proven difficult to study using traditional methods due to their transient nature and the heterogeneity of aggregation mixtures. In this thesis, I describe my work to develop advanced methods where I combine single-molecule and ensemble fluorescence techniques with microfluidic strategies to enable the study of protein aggregation, spanning small, transient oligomers to large, insoluble aggregates. In Chapter 1 I give an overview of the biological context and relevance of this work, including the background of neurodegenerative disease, amyloidogenic aggregation and key proteins involved. I then briefly review fluorescence microscopy techniques and the field of microfluidics. In Chapter 2 I describe how complex microfluidics can be integrated with single-molecule confocal techniques to provide a highly sensitive method to continuously probe protein aggregation in vitro. I show, for the first time, that the dilution of aggregating mixtures may be automated, by up to five orders of magnitude, down to the picomolar concentrations suitable for single-molecule measurements. By incorporating this microfluidic dilution device I greatly improve the temporal resolution of the technique and facilitate the observation of more transient species through the ability to rapidly dilute and take fluorescence measurements of samples. In Chapter 3 I overcome the need for in situ labels to monitor amyloidogenic aggregation using single-molecule confocal microscopy. I describe my work to adapt the single-molecule confocal technique to achieve the ultrasensitive detection of individual aggregate species under flow without covalently-attached labels. I have demonstrated the ability of this new method to monitor the aggregation of label-free amyloidogenic proteins using extrinsic labels ex-aggregation, opening the way for biological samples to be probed in a high-throughput manner. In Chapter 4 I describe my work to combine the high precision of confocal microscopy with a microfluidic device developed to directly characterise the sizes and interactions of biomolecules in the continuous phase. By monitoring the spatial and temporal mass transport on the micron scale, the diffusion coefficient, and thus hydrodynamic radius, of species may be determined. The technique delivers much greater sensitivity for size quantification, allowing scarce and other challenging samples to be characterised, and provides significant steps towards accurate sizing for single-molecule aggregation experiments under flow. In Chapter 5 I describe my work to determine the microscopic driving force for the spatial propagation of amyloid-beta. The epifluorescence instrument I built has enabled the proliferation of aggregate species to be monitored over a macro distance on a timescale of minutes. This has greatly improved the scope of the experimental data attained, which will be used in conjunction with Monte Carlo simulations to deliver a model for the propagation of amyloid-beta in vitro. Together this thesis represents my work developing the above novel fluorescence techniques to improve their temporal and size resolution, sensitivity and adaptability to study highly complex and fundamental protein aggregation linked to neurodegenerative disease.
Supervisor: Knowles, Tuomas ; Klenerman, David Sponsor: Frances and Augustus Newman Foundation
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: single-molecule ; fluorescence ; aggregation ; neurodegeneration ; microscopy