| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 99 === Prion protein (PrP) is an infectious species that is closely associated with prion diseases. PrP will become pathogenic when it undergoes structural change from its native α-helix (cellular PrP, PrPc) to β-sheet conformation (scrapie PrP, PrPsc). The molecular structure of the amyloid fibrils formed by the wild-type 127–147 peptide fragment of human prion protein (wild-type HuPrP127–147) adopts parallel β-sheet organization with in-registered alignment. There is a spatial constraint due to the side chain of proline, and this constraint may alter the molecular structure of the fibrils. Consequently, the mutation of the highly constrained P137 into other amino acids is a very interesting topic in biophysics.
In this study, we report the results of ThT fluorescence, TEM, CD, FT-IR, and solid-state NMR (SSNMR) data for the fibrils formed by both the wild type and P137A mutant of human prion protein 127–147 fragment. From the TEM data, various morphologies were observed in P137A mutant sample, depending on the incubation conditions. Surprisingly, the P137A mutants exhibit an additional self assembly at a relatively long length scale, viz. the formation of nanotube. The formation of nanotube is only observed under the dialysis conditions, which may facilitate the formation of β-sheet laminates. For the fibril samples prepared under the quiescent conditions, on the other hand, we find the evidence of bend-structure formation from the FT-IR data. Such bending structure most likely would preclude the formation of the nanotube. Consequently, the incubation conditions are crucial in the morphologenesis of our fibril systems. According to the SSNMR data, both the wild type and P137A mutant form in-registered parallel cross-β structures under quiescent incubation conditions, but morphology polymorphism have been observed for the mutant samples only. P137A mutant exhibits higher content of β sheets and faster fibrillization kinetics than the wild-type sample based on the CD and ThT experiments. In addition, the β-sheet structure of P137A mutant remains intact after sonification, whereas the wild-type sample becomes unstructured. These observations may be rationalized by the fact that proline would hinder β-sheet formation.
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