title: Acid-induced molten globule state of a prion protein: crucial role of Strand 1-Helix 1-Strand 2 segment.
abstract: The conversion of a cellular prion protein (PrP(C)) to its pathogenic isoform (PrP(Sc)) is a critical event in the pathogenesis of prion diseases. Pathogenic conversion is usually associated with the oligomerization process; therefore, the conformational characteristics of the pre-oligomer state may provide insights into the conversion process. Previous studies indicate that PrP(C) is prone to oligomer formation at low pH, but the conformation of the pre-oligomer state remains unknown. In this study, we systematically analyzed the acid-induced conformational changes of PrP(C) and discovered a unique acid-induced molten globule state at pH 2.0 termed the "A-state." We characterized the structure of the A-state using far/near-UV CD, 1-anilino-8-naphthalene sulfonate fluorescence, size exclusion chromatography, and NMR. Deuterium exchange experiments with NMR detection revealed its first unique structure ever reported thus far; i.e. the Strand 1-Helix 1-Strand 2 segment at the N terminus was preferentially unfolded, whereas the Helix 2-Helix 3 segment at the C terminus remained marginally stable. This conformational change could be triggered by the protonation of Asp(144), Asp(147), and Glu(196), followed by disruption of key salt bridges in PrP(C). Moreover, the initial population of the A-state at low pH (pH 2.0-5.0) was well correlated with the rate of the β-rich oligomer formation, suggesting that the A-state is the pre-oligomer state. Thus, the specific conformation of the A-state would provide crucial insights into the mechanisms of oligomerization and further pathogenic conversion as well as facilitating the design of novel medical chaperones for treating prion diseases.
authors.affiliation: School of Medicine and Gifu University, Yanagido 1-1, Gifu 501-1193, Japan.
authors.forename: Ryo P
authors.initials: RP
authors.lastname: Honda
authors.affiliation: United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, Yanagido 1-1, Gifu 501-1194, Japan.
authors.forename: Kei-Ichi
authors.initials: KI
authors.lastname: Yamaguchi
authors.affiliation: School of Medicine and Gifu University, Yanagido 1-1, Gifu 501-1193, Japan; United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, Yanagido 1-1, Gifu 501-1194, Japan; Department of Gene and Development, Graduate School of Medicine, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan and. Electronic address: kuwata@gifu-u.ac.jp.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kuwata
mesh_terms: D000818:Animals; D006863:Hydrogen-Ion Concentration; D051379:Mice; D010446:Peptide Fragments / Q000737:chemistry; D018621:PrPC Proteins / Q000737:chemistry*; D011328:Prions / Q000737:chemistry; D011489:Protein Denaturation; D055503:Protein Multimerization; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017186:Titrimetry; D014508:Urea / Q000737:chemistry
chemical_list: D010446:Peptide Fragments; D018621:PrPC Proteins; D011328:Prions; C507417:prion protein (90-231); D014508:Urea
keywords: A-state; Aggregation; Molten Globule State; Prion; Protein Dynamic; Protein Folding; Protein Misfolding; beta-rich Oligomer