| Protein self-assembly into amyloid fibrils are attracting increased attention for its notorious role in a variety of mammalian maladies. The most well known example is amyloid beta peptide (Abeta) that assembles into amyloid fibrils, and is tightly associated with the onset of Alzheimer's disease. Accumulating evidence showed that many proteins can form amyloid fibrils, indicating amyloidogenesis as an intrinsic property of proteins (Dobson 2003). Though considered extremely important, the structure, the assembly pathway and the regulatory factors of amyloid fibrils are still poorly understood. In this dissertation, self-assembly of several short peptides originating from amyloid-beta peptide was investigated and was specifically probed with metal ions.; This study established that Zn2+ is incorporated into Abeta(10-21) exclusively in the nucleation phase and induces short amyloid fibrils. Mutagenesis results supported that initiation of sheet-sheet contacts by Zn2+ is crucial for the formation of nucleus. In order to facilitate Zn2+ incorporation in propagation phase, Abeta(13-21)K16A was design, with exposure of His13/His 14 at peptide terminus. The results showed that Abeta(13-21)K16A indeed binds with Zn2+ on both nucleation and propagation phase. More profoundly, Abeta(13-21)K16A forms typical amyloid fibrils or novel twisted ribbons and nanotubes as a function of Zn2+ concentration. Different His-Zn2+-His coordination modes correlated with different morphologies have been defined, implying the importance of Zn2+-induced sheet-sheet contacts in amyloid formation.; The effect of Cu2+ ions on amyloid assembly was also explored, providing further constraints on amyloid structure. An inhibitory role of Cu2+ on the assembly of both Abeta(10-21) and Abeta(10-21)K16A was clearly demonstrated for the first time, resulting from peptide backbone deprotonation by Cu2+ even at acidic conditions. Based on this knowledge, I successfully designed a new peptide, Ac-Abeta(10-21)H14A, in which Cu2+-induced peptide backbone ionization is eliminated, and both Zn2+ and Cu2+ accelerate amyloid fibril formation with a His-metal-His coordination mode.; This research work provides new insights into the structure of amyloid fibrils and protein self-assembly. The assembled structures, with such ordered and dense packed metal ion sites exposed on the surface, open the possibility to engineer unique catalytic chemistry. |
