title: On the mechanism of alpha-helix to beta-sheet transition in the recombinant prion protein.
abstract: It is believed that the critical event in the pathogenesis of transmissible spongiform encephalopathies is the conversion of the prion protein from an alpha-helical form, PrP(C), to a beta-sheet-rich conformer, PrP(Sc). Recently, we have shown that incubation of the recombinant prion protein under mildly acidic conditions (pH 5 or below) in the presence of low concentrations of guanidine hydrochloride results in a transition to PrP(Sc)-like beta-sheet-rich oligomers that show fibrillar morphology and an increased resistance to proteinase K digestion [Swietnicki, W., Morillas, M, Chen, S., Gambetti, P., and Surewicz, W. K. (2000) Biochemistry 39, 424-431]. To gain insight into the mechanism of this transition, in the present study we have characterized the biophysical properties of the recombinant human prion protein (huPrP) at acidic pH in the presence of urea and salt. Urea alone induces unfolding of the protein but does not result in protein self-association or a conversion to beta-sheet structure. However, a time-dependent transition to beta-sheet structure occurs upon addition of both urea and NaCl to huPrP, even at a sodium chloride concentration as low as 50 mM. This transition occurs concomitantly with oligomerization of the protein. At a given protein and sodium chloride concentration, the rate of monomeric alpha-helix to oligomeric beta-sheet transition is strongly dependent on the concentration of urea. Low and medium concentrations of the denaturant accelerate the reaction, whereas strongly unfolding conditions are not conducive to the conversion of huPrP into an oligomeric beta-sheet-rich structure. The present data strongly suggest that partially unfolded intermediates may be involved in the transition of the monomeric recombinant prion protein into the oligomeric scrapie-like form.
authors.affiliation: Department of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: M
authors.initials: M
authors.lastname: Morillas
authors.forename: D L
authors.initials: DL
authors.lastname: Vanik
authors.forename: W K
authors.initials: WK
authors.lastname: Surewicz
mesh_terms: D002021:Buffers; D002942:Circular Dichroism; D006801:Humans; D007700:Kinetics; D008027:Light; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D018620:PrPSc Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D012492:Salts; D012542:Scattering, Radiation; D019346:Sodium Acetate; D012965:Sodium Chloride; D014508:Urea / Q000737:chemistry
chemical_list: D002021:Buffers; D010446:Peptide Fragments; D018620:PrPSc Proteins; D011994:Recombinant Proteins; D012492:Salts; D012965:Sodium Chloride; D019346:Sodium Acetate; D014508:Urea