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Title: Smart nanomaterials from repeat proteins and amyloid fibrils
Author: Guttenplan, Alexander Pandias Margaronis
ISNI:       0000 0004 7227 0042
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2018
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Protein-based materials are an important area of research for various reasons. Natural protein materials such as spider silk have mechanical properties which compare favourably to artificial or inorganic materials, and in addition are biodegradable and can be produced from easily available feedstocks. It is also possible to produce materials that incorporate the functionality of a natural protein, such as ligand-binding or catalysis of reactions, thus allowing this functionality to be used in the solid rather than solution phase. Two particularly interesting components for protein-based materials are amyloid fibrils and tandem repeat proteins. Amyloid fibrils are exceptionally strong, tough, highly-ordered structures that self-assemble from a wide range of simple building blocks. Meanwhile, tandem repeat proteins are a class of proteins that act as scaffolds to mediate protein-protein interactions and are known to act as elastic springs. Unlike globular proteins, tandem repeat proteins can be designed to bind specific ligands, and their ligand-binding properties and stability can be tuned separately. This work details the synthesis and characterisation of repeat protein and amyloid fibril components for a “smart” hydrogel, the production of these gels, and their characterisation using a microfluidic method that I developed. Although amyloid fibrils have previously been decorated with functional proteins, hitherto, this has usually been done by assembling the fibrils from already-functionalised components. This approach limits the functionality to species that can survive the harsh conditions of amyloid aggregation and do not disturb fibril assembly. Therefore, a method was developed to produce amyloid fibrils that displayed an alkyne functionality on their surface to allow functional proteins or other species to be attached after assembly. This involved the design and synthesis (using solid-phase peptide chemistry) of a peptide based on the previously known TTR105-115 peptide (derived from the amyloidogenic Transthyretin protein). These fibrils were characterised by AFM and TEM and it was then shown that the assembled fibrils could be functionalised using an azide-alkyne “click” reaction. The reaction was shown to work with a variety of ligands including proteins, which were found to retain their structure and function after crosslinking to the fibril. The fibrils with ligands attached were characterised by a variety of methods including LCMS (liquid chromatography-mass spectrometry) and super-resolution optical microscopy. Next, repeat proteins were produced recombinantly containing non-natural azido amino acids at their termini. Incorporation of non-natural amino acids was carried out using a number of different methods including amber codon suppression and methionine replacement. Micron-sized hydrogels were then formed from microfluidic-generated droplets by covalently crosslinking the alkyne-functionalised fibrils with the azide-functionalised repeat proteins. The initial experiments to show proof of principle were carried out with consensus-designed repeat proteins, but repeat proteins based on natural sequences were also used to make hydrogels that could later be tested for potential uptake of peptides known to bind these proteins. These hydrogels could potentially be used for drug delivery or other applications in which a chemical response to a mechanical stimulus is desired. The mechanical properties of the hydrogels were measured using novel microfluidic devices, which were designed and fabricated using standard PDMS-based soft lithography.
Supervisor: Itzhaki, Laura Susan ; Knowles, Tuomas Pertti Jonathan Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Protein-based nanotechnology ; Repeat protein ; Amyloid fibrils ; Microgels ; Microfluidics ; Hydrogels ; Protein engineering ; Non-natural amino acids