Graduation Year

2019

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

Martin M. Muschol, Ph.D.

Committee Member

Zhimin Shi, Ph.D.

Committee Member

Jianjun Pan, Ph.D.

Committee Member

Piyush Koria, Ph.D.

Keywords

Amino Acids, Amyloid β Aggregation, Carbonyl Double Bond, Cytotoxicity, Deep-blue Autofluorescence, Lysozyme

Abstract

Amyloidosis is a group of diseases in which amyloid fibrils accumulate and deposit into plaques and intracellular inclusions which lead to disruption of the tissue architecture and function. Most of the amyloid diseases are incurable due to a lack of understanding of the amyloid formation, as well as associated toxicity. My research work is focused on three different aspects of amyloid aggregation.

The aim of the first project is to investigate the potential use of deep-blue autofluorescence (dbAF) as an intrinsic optical probe to study amyloid self-assembly. This novel fluorescence signal is excited at the long wavelength edge of the UV and emits in the deep blue and believed to emerge as a result of protein aggregation. However, we are able to show that dbAF is present at the level of monomeric proteins and even poly- and single amino acids. We are interested in finding the molecular origin of this fluorescence signal and our data implicates the carbonyl double bonds in amino acids as the likely source. Furthermore, we have shown that dbAF is sensitive to both the chemical identity and solution environment of amino acids and has the potential to use as a tool for studying the structure and dynamics of amino acids, proteins and, by extension, DNA and RNA.

The amyloid aggregate species mediate the cytotoxicity associated with many amyloid disorders still remain elusive. In the second project, the focus is to investigate the cytotoxicity of oligomeric vs. fibrillar amyloid aggregates formed by hen egg white lysozyme (HEWL). Both of these amyloid aggregates form macroscopic structures once they are transferred to physiological media from growth conditions. The HEWL oligomeric species form gel-like clusters similar to diffuse plaques in Alzheimer’s patients and show no significant toxicity in cell culture experiments. Conversely, fibrillar plaques with the ordered internal structure are analogous to neuritic plaques and induced toxic effects to the cells. However, interestingly, the most toxic effect is observed from the background solution of the fibrillary aggregates. Our data reveal that these background solutions contain amyloidogenic oligomeric species which differ from monomer derived oligomers in origin, structure, and toxicity.

The third project is focused on studying the mechanisms of amyloid β peptide aggregation associated with Alzheimer’s disease. Previously we have shown that amyloid aggregation occurs in two different pathways, oligomeric and oligomer-free for two different amyloid proteins. Using amyloid β 1-40 and 1-42 peptides, we show a sharp transition in the kinetics of amyloid assembly as a function of peptide concentration, from oligomer-free to oligomer-dominated rigid fibril formation under near-physiological conditions.

Download

Share

COinS