| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 95 === Prion disease, a kind of neurodegenerative disease, is commonly believed to be caused by the conversion of the prion protein from its normal cellular form (PrPC) to the disease-specific form (PrPSc). However, the mechanism of fibrillization is still unclear. It is suggested that the presence of PrPSc will induce the misfolding of other PrPC to PrPSc, damaging the nervous system of the victims. Because PrPSc has a strong propensity to form amyloid fibrils, which are insoluble in common solvents and are non-crystalline in nature, it is difficult to use solution-state NMR or X-ray diffraction technique to study PrPSc. Consequently, solid-state NMR is well suited to study PrPSc. Our target is to employ solid-state NMR spectroscopy to investigate the molecular structure of the amyloid fibrils formed by the peptide fragment of prion protein.
In this thesis, our target peptide sequence is the fragment 109 to 122 of Syrian hamster prion protein, MKHMAGAAAAGAVV, which is believed to be the most amyloidogenic region. We successfully obtained fibril sample from the target peptide and characterized the morphology of the fibrils by TEM and AFM. The fibrils in general have a length over 400 nm, a width of 11 nm, and a uniform height of 0.9 ± 0.1 nm. From the chemical shift and linewidth data , the beta-strands forming the fibrils have significant structural order in the hydrophobic region. We measured the backbone Ψ angle values and analysis the linewidth and second chemical shift and found the residues in the hydrophobic region form well-structure area. Furthermore, we found that each fibril comprises of two cross-beta layers. The beta strands within each layer are anti-parallel and aligned in such a way that the Ala 117 forms a linear chain along the fibril axis. Consequently, a molecular model for the fibrils was constructed by molecular dynamics simulations incorporated with structural constraints obtained from solid-state NMR measurements.
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