Graduation Year

2016

Document Type

Thesis

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

Martin Muschol, Ph.D.

Committee Member

W. Garrett Matthews, Ph.D.

Committee Member

Ghanim Ullah, Ph.D.

Committee Member

Sagar Pandit, Ph.D.

Committee Member

Vladimir Uversky, Ph.D.

Keywords

Lysozyme, Transthyretin, Beta2-micro globulin, Prion, Polyglutamic Acid, Dynamic Light Scattering

Abstract

Growth and deposition of amyloid fibrils, polymers of proteins with a cross beta-sheet structure, are associated with a significant number of human pathologies including Alzheimer’s disease, Parkinson’s disease, prion diseases, type II diabetes, and senile systematic or dialysis-related amyloidoses. The broader objective of my research is to identify the basic mechanisms regulating nucleation and growth of amyloid fibrils. There is increasing evidence that amyloid formation may proceed along at least two distinct assembly pathways for the formation of rigid fibrils. One pathway involves the nucleated polymerization of the characteristic rigid fibrils from partially denatured monomers and the other proceeds via the growth of globular oligomers and their associated curvilinear fibrils (also known as protofibrils) which, in ways yet to be determined, transform into late-stage rigid fibrils. These oligomeric intermediates of fibril assembly, in particular, have been implicated as the predominant aggregate species causing cellular toxicity in amyloid diseases. Yet, amyloid oligomers and curvilinear fibrils are considered transient, metastable aggregates. This raises the question whether and how such transient aggregate species can be responsible for most of the cell/tissue toxicity?

In this dissertation, I report on my investigation of several basic questions related to the mechanisms of amyloid formation. Using the model amyloid hen egg-white lysozyme, I participated in research to characterize the distinct kinetics of amyloid formation along distinct assembly pathways, to determine the morphological features of the various aggregate species emerging along either pathway, and to investigate the structural evolution of the monomers from their native state to the amyloid cross- sheet structure (chapter 3). Chapters 4-6 represent the core of my dissertation work. There I investigated whether amyloid aggregates from three different amyloid proteins, formed under denaturing condition, could undergo prion-like proliferation upon return to physiological solution conditions. I was also intimately involved in a project on the conditions inducing amyloid spherulites formation by polyglutamic acid and the mechanisms resulting in the formation of this often-overlooked amyloid aggregate structure (chapter 7). In the appendix I provide a short summary of the various experimental techniques I have used in the above experiments.

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