Molecular Structure of Proline Containing Amyloid Fibrils Formed by Residues 127 to 147 of the Human Prion Protein
Date Issued
2008
Date
2008
Author(s)
Lin, Ni-Shine
Abstract
Prion disease is a kind of amyloid disease, which is caused by the conversion of prion protein from its normal cellular form (cellular prion protein, PrPC) to the disease-specific form (scrapie prion protein, PrPSc). PrPSc exists in the form of amyloid fibrils, which are inherent insoluble and non-crystalline solids. Due to this reason, the detailed structural information of PrPSc is difficult to obtain by conventional techniques such as X-ray crystallography or solution-state NMR. It has recently been shown that solid-state nuclear magnetic resonance (SSNMR) is a particularly useful method for the structural elucidation of amyloid fibrils. In our study, amyloid fibrils are prepared by incubating the peptide fragment of human prion protein (HuPrP127-147), Ac-GYMLGSAMSRPIIHFGSDYED-NH2, in PBS at 37?C. HuPrP127-147 is believed to be an infectious fragment of the amyloidogenic region. In addition, HuPrP127-147 contains a proline residue, whose structure is highly constrained. Therefore, studying the fibrillar structure of HuPrP127-147 is an interesting topic of biophysics. Accordingly, ThT fluorescence spectra are obtained to confirm the fibril formation and the fibril morphology is studied by TEM and AFM. The fibrils have twist morphology and the twist period is about 70 to 80 nm The fibril height is between 3 and 4 nm. SSNMR measurements are carried out to probe for the molecular structure of the fibril samples. Our data show that the fibrils are formed by parallel in-registered alignment of peptides adopting b-strand conformation. In particular, each peptide constituting the fibrils has a b-strand region, viz. 129-142. With the proline (P137) as the boundary, the b-strand region near the N terminal (b1) has higher structural order than that near the C terminus (b2), which is associated with considerable dynamic motions. We also use FT-IR measurements to detect the vibrational dipole coupling in isotope-edited polypeptides. The results show that the b1 region conforms to the cross-b structure, but not the b2 region. We speculate that the b2 region is mainly stabilized by the side-chain-side-chain interactions.
Subjects
amyloid fibril
solid state NMR
SDGs
Type
thesis
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