Hydration and Packing Effects on Prion Folding and β-Sheet Conversion

• Published in: The Journal of biological chemistry Vol. 279; no. 31; p. 32354
• Main Authors: Yraima Cordeiro, Julia Kraineva, Revanur Ravindra, Luís Maurício T. R. Lima, Mariana P. B. Gomes, Debora Foguel, Roland Winter, Jerson L. Silva
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 30.07.2004
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M404295200

The main hypothesis for prion diseases proposes that the cellular protein (PrP C ) can be altered into a misfolded, β-sheet-rich isoform (PrP Sc ), which undergoes aggregation and triggers the onset of transmissible spongiform encephalopathies. Here, we compare the stability against pressure and the thermomechanical properties of the α-helical and β-sheet conformations of recombinant murine prion protein, designated as α-rPrP and β-rPrP, respectively. High temperature induces aggregates and a large gain in intermolecular antiparallel β-sheet (β-rPrP), a conformation that shares structural similarity with PrP Sc . α-rPrP is highly stable, and only pressures above 5 kilobars (1 kilobar = 100 MegaPascals) cause reversible denaturation, a process that leads to a random and turnrich conformation with concomitant loss of α-helix, as measured by Fourier transform infrared spectroscopy. In contrast, aggregates of β-rPrP are very sensitive to pressure, undergoing transition into a dissociated species that differs from the denatured form derived from α-rPrP. The higher susceptibility to pressure of β-rPrP can be explained by its less hydrated structure. Pressure perturbation calorimetry supports the view that the accessible surface area of α-rPrP is much higher than that of β-rPrP, which explains the lower degree of hydration of β-rPrP. Our findings shed new light on the mechanism of prion conversion and show how water plays a prominent role. Our results allow us to propose a volume and free energy diagram of the different species involved in the conversion and aggregation. The existence of different folded conformations as well as different denatured states of PrP may explain the elusive character of its conversion into a pathogenic form.