Reversible monomer-oligomer transition in human prion protein

Abstract

The structure and the dissociation reaction of oligomers PrP oligo from reduced human prion huPrP C (23-231) have been studied by 1 H-NMR and tryptophan fluorescence spectroscopy at varying pressure, along with circular dichroism and atomic force microscopy. The 1 H-NMR and fluorescence spectral feature of the oligomer is consistent with the notion that the N-terminal residues including all seven Trp residues, are free and mobile, while residues 105~210, comprising the AGAAAAGA motif and S1-Loop-HelixA-Loop-S2-Loop-HelixC, are engaged in intra-and/ or inter-molecular interactions. By increasing pressure to 200 MPa, the oligomers tend to dissociate into monomers which may be identified with PrP C* , a rare metastable form of PrP C stabilized at high pressure (Kachel et al., BMC Struct Biol 6:16). The results strongly suggest that the oligomeric form PrP oligo is in dynamic equilibrium with the monomeric forms via PrP C* , namely huPrP C  huPrP C*  huPrP oligo .

Conformational Properties of β-PrP

“…From 15 N studies on ␣-PrP (6, 59), we can conclude that, as in ␣-PrP, these residues are predomi-nantly unstructured (58). This is in contrast to full-length ␤-PrP (residues 23-231), where residues 105-210 appear to be engaged in intra-and/or intermolecular interactions (35). The NMR characteristics of ␤-PrP appear similar to other partially folded molten globule and oligomeric states of PrP (30,32,33), which also contain a predominantly disordered N-terminal region (residues 91-126) and a line broadened, unobservable region corresponding to the folded domain of ␣-PrP.…”

“…Subsequently, a related study examining the role of the disulfide bond in PrP folding confirmed that a monomeric molten globule-like form of PrP was formed on refolding the disulfide-reduced protein at acidic pH, but reported that, under their conditions, the circular dichroism response interpreted as ␤-sheet structure was associated with protein oligomerization (45). Indeed, atomic force microscopy on oligomeric full-length ␤-PrP (residues 23-231) shows small, round particles, showing that it is capable of formation of oligomers without forming fibrils (35). Notably, however, saltinduced oligomeric ␤-PrP has been shown to be a potent inhibitor of the 26 S proteasome, in a similar manner to PrP Sc (46).…”

“…One such PrP folding intermediate, termed ␤-PrP, differs from the majority of studied PrP intermediate states in that it is formed by refolding the PrP molecule from the native ␣-helical conformation (here termed ␣-PrP), at acidic pH in a reduced state, with the disulfide bond broken (22,35). Although no covalent differences between the PrP C and PrP Sc have been consistently identified to date, the role of the disulfide bond in prion propagation remains disputed (25, 36 -39).…”

“…Although no covalent differences between the PrP C and PrP Sc have been consistently identified to date, the role of the disulfide bond in prion propagation remains disputed (25, 36 -39). ␤-PrP is rich in ␤-sheet structure (22,35), and displays many of the charac-teristics of a PrP Sc -like precursor molecule, such as partial resistance to proteinase K digestion, and the ability to form amyloid fibrils in the presence of physiological concentrations of salts (40).…”

Ceramic cells for high pressure NMR spectroscopy of proteins

“…By observing the pressure response of proteins one obtains not only data on the local and global mechanical and dynamical properties of the macromolecule [4] but can also shift conformational equilibria and stabilize folding and functional intermediates [5][6][7][8]. In addition, physicochemical processes such as pressure induced denaturation, depolymerization, and dissociation can be studied in detail [7,9,10].…”