Solution-State NMR Studies of Salivary Protein Fragment and Human Prion Peptide
Date Issued
2009
Date
2009
Author(s)
Chu, Wen-Chi
Abstract
Solution-state NMR is a powerful method for the structural studies of polypeptides and proteins. Two types of polypeptides are discussed in this work. Human saliva is a supersaturated solution of calcium phosphates, which provides a protective and reparative environment for dental enamel and dentin. Precipitation of calcium phosphates in saliva is inhibited by an acidic phosphoprotein, statherin, which contains 43 residues. The function of statherin is mainly provided by a 15-residue (D1pSpSEEKFLRRIGRFG15) fragment near the N-terminus, viz. SN-15. In this work, we investigate the conformation of SN-15 in aqueous solution with solution-state NMR technique. High resolution 1H-1H NMR spectra (COSY, TOCSY, and NOESY) have been acquired in aqueous solution. Amide hydrogen exchange experiment indicates that SN-15 adopts an α-helical structure. The peptide structure of atomic scale resolution has been successfully calculated from the NMR constrains. The solution structure determined for SN-15 shows that the residues of K6, F7, L8, and R9 exhibit a helical structure, whereas the first 5 residues of the N-terminus are in helix-like conformation. Additional NMR measurements show that the structure of the SN-15 peptide in the supersaturated calcium ion and calcium phosphate solution is essentially the same as that determined in regular pH buffer. This interesting result indicates that the interactions between the SN-15 and calcium phosphates are mainly electrostatic in nature and do not involve any major conformational changes.rion protein (PrP) is closely associated with prion diseases. PrP will become pathogenic when it undergoes structural change from its native α-helix to β-sheet form. In particular, we attempt to study the human PrP fragment compassing residue 106-114, which is highly hydrophilic. We find that the peptides do not form insoluble fibrils after incubation and therefore solution-state NMR is used to characterize its structure. Soluble protofibrils were observed for the HuPrP106-114 peptides from the electron microscopy. Analysis of CD and NMR spectra show that the secondary structure of the HuPrP106-114 peptide is random-coil in aqueous solution. This results indicate that fibril formation for HuPrP106-114 may involve a structural rearrangement of the random aggregate formed by the peptides.
Subjects
solution-state NMR
statherin
hydroxyapatite
prion protein
amloid fibril
protofibril
random aggregate
SDGs
Type
thesis
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