Physical studies of conformational plasticity in a recombinant prion protein.

PrPSc is known to be the major, if not the only, component of the infectious prion. Limited proteolysis of PrPSc produces an N-terminally truncated polypeptide of about 142 residues, designated PrP 27−30. Recently, a recombinant protein (rPrP) of 142 residues corresponding to the Syrian hamster PrP 27−30 was expressed in Escherichia coli and purified (Mehlhorn et al., 1996). rPrP has been refolded into both α-helical and β-sheet structures as well as various intermediates in aqueous buffers. The β-sheet state and two pH-dependent α-helical states were characterized by CD and NMR. The α-helical conformation occurred only after the formation of an intramolecular disulfide bond, whereas the β-sheet form was accessible either with or without the disulfide. Of the different α-helical forms studied, only those refolded in the pH range 5−8 were substantially soluble at physiological pH, exhibiting similar conformations and monomeric analytical sedimentation profiles throughout the above pH range. Furthermore, re...