Doctor of Philosophy (PhD)
This work demonstrates peptide-based aggregation mediation of fibril forming peptides, notably β-amyloid (1-40), Aβ1-40. To achieve the goals of this work, Aβ1-40 aggregation was governed by ionic strength, temperature, and pH. After controlling and reproducing Aβ1-40 aggregate formation (fibrils), each peptide-based aggregation mediator was evaluated for its ability to self-aggregate and to possess surface-active properties. The incorporation of these mediators in Aβ1-40 solutions changed the surface tension and produced aggregate complexes of mediator and Aβ1-40. Evidence that Aβ1-40 fibril formation may be mediated by disorder-to-order transitions has been observed by layer formation on top of a β-sheet monolayer of another fibril forming, but cyclic, peptide. Governance of Aβ1-40 aggregation was performed by controlling the environment (ionic strength and temperature) of both the stock and sample conditions. Sample containment was important in controlling aggregation, as a certain brand of vessels induced Aβ1-40 aggregation. Each peptide-based aggregation mediator was characterized to determine any self-aggregation. It was found that AMY-1, developed at Louisiana State University, and an inhibitor developed by Dr. Regina Murphy at the University of Wisconsin sparsely aggregated. AMY-2, also developed at L.S.U., favored deposition on mica. The Murphy inhibitor produced no change in surface activity over a wide concentration range, while AMY-1 and AMY-2 displayed surface activity and critical micelle concentrations just below 1 mM. The introduction of some mediators displayed changes in surface tension to solutions of Aβ1-40; Murphy’s inhibitor increased the surface tension, whereas AMY-1 and AMY-2 decreased the surface tension of Aβ1-40 solutions. Complex formation between each mediator and Aβ1-40 inhibited fibril formation and formation of amorphous aggregates, as evidenced by scanning force and transmission electron microscopy. The adsorption of a monolayer of Aβ1-40 onto a β-sheet monolayer of cyclic peptides was observed. These cyclic peptides, initially thought to be fibril inhibitors, were found to be potent fibril formers themselves and attached only to exposed sites of highly oriented pyrolytic graphite. The ability for a surface to induce fibril formation may allow a more thorough understanding of Aβ1-40 fibril formation.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Aucoin, Jed Paul, "Protein aggregation studies: inhibiting and encouraging β-amyloid aggregation" (2004). LSU Doctoral Dissertations. 1839.