The polymorphic nature of amyloid assembly: Exploring fibril morphology and the structural relationship towards mechanical stability

The polymorphic nature of amyloid fibrils is important in the understanding of structural based relationships, such as a morphology influence on cytotoxicity and disease progression. The work reported here uses Atomic force microscopy (AFM) to enhance the understanding of fibril morphology in addition to the relationship between structure and stability towards breakage. A novel quantitative cluster analysis was developed here to identify the vast range of fibril morphologies present within a population. Using fibrils formed from three peptide sequences identified by the WALTZ algorithm, we have characterised the polymorphism displayed by each fibril population and provided structural models to predict the likely filament arrangements accessible to each. The range of fibril polymorphism also conveys mechanical differences, defined here by persistence length values for each respective population. These mechanical differences subsequently affect fibrils stability towards breakage, quantified here using AFM and subsequent image analysis. Additionally, using AFM, a structural comparison was performed between Sup35NM amyloid fibrils formed in vitro and those formed in situ using a synthetic biology approach with the Curli-dependent amyloid generator (C-DAG) in E. Coli. Structural similarities between fibrils formed using this system and those formed in vitro is of great value given the importance of a sequence-structure relationship. The work in this thesis expands on possible fibril morphologies and the related mechanical properties, which has implications in the understanding of disease enhancing structural motifs and the utilisation of amyloid fibrils in a biotechnology role