Oligomerization of the Human Prion Protein Proceeds via a Molten Globule Intermediate

• Published in: The Journal of biological chemistry 2007-03, Vol.282 (9), p.6300-6307
• Main Authors: Gerber, Remo, Tahiri-Alaoui, Abdessamad, Hore, P.J., James, William
• Format: Article
• Language: English
• Subjects: Amyloid - chemistry; Dimerization; Humans; Magnetic Resonance Spectroscopy; Prions - chemistry; Protein Conformation; Protein Folding; Protein Structure, Secondary
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M608926200

The conformational transition of the human prion protein from an α-helical to a β-sheet-rich structure is believed to be the critical event in prion pathogenesis. The molecular mechanism of misfolding and the role of intermediate states during this transition remain poorly understood. To overcome the obstacle of insolubility of amyloid fibrils, we have studied a β-sheet-rich misfolded isoform of the prion protein, the β-oligomer, which shares some structural properties with amyloid, including partial proteinase resistance. We demonstrate here that the β-oligomer can be studied by solution-state NMR spectroscopy and obtain insights into the misfolding mechanism via its transient monomeric precursor. It is often assumed that misfolding into β-sheet-rich isoforms proceeds via a compatible precursor with a β-sheet subunit structure. We show here, on the contrary, evidence for an almost natively α-helix-rich monomeric precursor state with molten globule characteristics, converting in vitro into the β-oligomer. We propose a possible mechanism for the formation of the β-oligomer, triggered by intermolecular contacts between constantly rearranging structures. It is concluded that the β-oligomer is not preceded by precursors with β-sheet structure but by a partially unfolded clearly distinguishable α-helical state.