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.