Derived amyloid fibrils to act as nuclei for the polymerization of full-length PrP would shed light upon the relative importance of different regions as cores for PrP amyloid formation. In this study, three synthetic peptides, mPrP(107?43), mPrP(107?26), and mPrP(127?43), were synthesized and the amyloid fibrils formed from these three peptides were used as seeds to determine the segment within sequence 107?143 which can act as the core region in prion protein amyloidogenesis in vitro, based on the ability of these peptides to cross-seed full-length prion protein mPrP(23?30).lysate was incubated with 0.2 mg/mL of lysozyme and 0.1 mM PMSF for 40 min with continuous stirring, then 1 mg/mL of deoxycholic acid was added and the mixture was incubated for 45 min, followed by addition of 5 mg/mL of DNase I and further 45 min incubation. Inclusion bodies were harvested by centrifugation of the lysate at 12,000g for 30 min at 4uC and solubilized in buffer A (8 M urea, 0.1 M Na2HPO4, 10 mM Tris-HCl, 10 mM reduced glutathione, pH 8.0). After centrifugation at 20000g for 30 minutes at 4uC, the soluble fraction was loaded onto a prepacked Ni column (HisTrapTM FF 1 mL, Amersham Biosciences) previously equilibrated with buffer A and non-bound proteins were removed by washing. Then mPrP(23?30) was eluted with buffer A at pH 4.5. The eluted protein was desalted on a HiPrepTM 26/10 desalting column (Amersham Biosciences) at room temperature using 6 M urea, 0.1 M Tris-HCl, pH 7.5, as desalting buffer. Disulfide bond formation of the prion protein was induced by overnight oxidation at room temperature in the presence of 0.2 mM oxidized glutathione and 5 mM EDTA. The oxidized protein was purified at room temperature by reversephase Title Loaded From File chromatography on a C5 column (Discovery BIO Wide Pore C5, 10 mm, 25 cm610.0 mm, Supelco, USA) with a 30 min Title Loaded From File linear gradient of 28?3 of buffer B (acetonitrile containing 0.1 trifluoroacetic acid). Oxidized mPrP(23?30) was eluted at about 33.3 of buffer B. The eluted protein was lyophilized and identified by ESI-TOF mass spectrometry and SDS-PAGE and stored at 230uC.Thioflavin T (ThT) Binding AssayAmyloid fibril formation of spontaneous and seeded amyloidogenesis of mPrP(23?30) was monitored using the Thioflavin T (ThT) binding assay [34]. Briefly, 30 mL of 200 mM ThT in 140 mM NaCl, 100 mM phosphate buffer (pH 8.5) was mixed with 30 mL of fibril solution for 1 min at room temperature and the fluorescence emission between 460 and 600 nm was measured in a 3-mm path-length rectangular cuvette in a FP-750 spectrofluorometer (JASCO, Japan) with excitation at 442 nm. Both excitation and emission slits were set at 5 nm.Materials and Methods Peptide SynthesisThe prion peptides used were synthesized using the Fmocpolyamide method on a PS3 peptide synthesizer (Rainin, USA) [32]. The N- and C-terminal ends of the peptides were acetylated and amidated, respectively, in order to mimic the polypeptide bond in the full-length protein. The peptides were characterized by mass spectrometry after purification. After lyophilization, the peptides were stored at ?0uC.Spontaneous Amyloid Fibril Formation by Mouse Prion Protein 23977191 and PeptidesPurified recombinant mPrP(23?30) was dissolved in 6 M guanidine hydrochloride (GdnHCl) as a 132 mM stock solution. For fibrillization, 100 mL of the stock solution was diluted to 22 mM in 300 mL of fibril formation buffer (2x phosphate-buffered saline (PBS), 6 M urea, pH 6.0) and 200 mL of de-ionized water to give.Derived amyloid fibrils to act as nuclei for the polymerization of full-length PrP would shed light upon the relative importance of different regions as cores for PrP amyloid formation. In this study, three synthetic peptides, mPrP(107?43), mPrP(107?26), and mPrP(127?43), were synthesized and the amyloid fibrils formed from these three peptides were used as seeds to determine the segment within sequence 107?143 which can act as the core region in prion protein amyloidogenesis in vitro, based on the ability of these peptides to cross-seed full-length prion protein mPrP(23?30).lysate was incubated with 0.2 mg/mL of lysozyme and 0.1 mM PMSF for 40 min with continuous stirring, then 1 mg/mL of deoxycholic acid was added and the mixture was incubated for 45 min, followed by addition of 5 mg/mL of DNase I and further 45 min incubation. Inclusion bodies were harvested by centrifugation of the lysate at 12,000g for 30 min at 4uC and solubilized in buffer A (8 M urea, 0.1 M Na2HPO4, 10 mM Tris-HCl, 10 mM reduced glutathione, pH 8.0). After centrifugation at 20000g for 30 minutes at 4uC, the soluble fraction was loaded onto a prepacked Ni column (HisTrapTM FF 1 mL, Amersham Biosciences) previously equilibrated with buffer A and non-bound proteins were removed by washing. Then mPrP(23?30) was eluted with buffer A at pH 4.5. The eluted protein was desalted on a HiPrepTM 26/10 desalting column (Amersham Biosciences) at room temperature using 6 M urea, 0.1 M Tris-HCl, pH 7.5, as desalting buffer. Disulfide bond formation of the prion protein was induced by overnight oxidation at room temperature in the presence of 0.2 mM oxidized glutathione and 5 mM EDTA. The oxidized protein was purified at room temperature by reversephase chromatography on a C5 column (Discovery BIO Wide Pore C5, 10 mm, 25 cm610.0 mm, Supelco, USA) with a 30 min linear gradient of 28?3 of buffer B (acetonitrile containing 0.1 trifluoroacetic acid). Oxidized mPrP(23?30) was eluted at about 33.3 of buffer B. The eluted protein was lyophilized and identified by ESI-TOF mass spectrometry and SDS-PAGE and stored at 230uC.Thioflavin T (ThT) Binding AssayAmyloid fibril formation of spontaneous and seeded amyloidogenesis of mPrP(23?30) was monitored using the Thioflavin T (ThT) binding assay [34]. Briefly, 30 mL of 200 mM ThT in 140 mM NaCl, 100 mM phosphate buffer (pH 8.5) was mixed with 30 mL of fibril solution for 1 min at room temperature and the fluorescence emission between 460 and 600 nm was measured in a 3-mm path-length rectangular cuvette in a FP-750 spectrofluorometer (JASCO, Japan) with excitation at 442 nm. Both excitation and emission slits were set at 5 nm.Materials and Methods Peptide SynthesisThe prion peptides used were synthesized using the Fmocpolyamide method on a PS3 peptide synthesizer (Rainin, USA) [32]. The N- and C-terminal ends of the peptides were acetylated and amidated, respectively, in order to mimic the polypeptide bond in the full-length protein. The peptides were characterized by mass spectrometry after purification. After lyophilization, the peptides were stored at ?0uC.Spontaneous Amyloid Fibril Formation by Mouse Prion Protein 23977191 and PeptidesPurified recombinant mPrP(23?30) was dissolved in 6 M guanidine hydrochloride (GdnHCl) as a 132 mM stock solution. For fibrillization, 100 mL of the stock solution was diluted to 22 mM in 300 mL of fibril formation buffer (2x phosphate-buffered saline (PBS), 6 M urea, pH 6.0) and 200 mL of de-ionized water to give.
