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Department of Chemistry and Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
(RECEIVED February 25, 2005; FINAL REVISION May 19, 2005; ACCEPTED May 19, 2005)
Prion diseases appear to be caused by the aggregation of the cellular prion protein (PrPC) into an infectious form denoted PrPSc. The in vitro aggregation of the prion protein has been extensively investigated, yet many of these studies utilize truncated polypeptides. Because the C-terminal portion of PrPSc is protease-resistant and retains infectivity, it is assumed that studies on this fragment are most relevant. The full-length protein can be distinguished from the truncated protein because it contains a largely structured, 
-helical, C-terminal region in addition to an N terminus that is unstructured in the absence of metal ion binding. Herein, the in vitro aggregation of a truncated portion of the prion protein (PrP 90–231) and a full-length version (PrP 23–231) were compared. In each case, concentration-dependent aggregation was analyzed to discern whether it proceeds by a nucleation-dependent pathway. Both protein constructs appear to aggregate via a nucleated polymerization with a small nucleus size, yet the later steps differ. The full-length protein forms larger aggregates than the truncated protein, indicating that the N terminus may mediate higher-order aggregation processes. In addition, the N terminus has an influence on the assembly state of PrP before aggregation begins, causing the full-length protein to adopt several oligomeric forms in a neutral pH buffer. Our results emphasize the importance of studying the full-length protein in addition to the truncated forms for in vitro aggregation studies in order to make valid hypotheses about the mechanisms of prion aggregation and the distribution of aggregates in vivo.
Keywords: prion protein; aggregation; full-length prion protein; N-terminal domain
Abbreviations: PrP, prion protein • PrPC, cellular form of the prion protein • PrPSc, scrapie/infective form of the prion protein • PrP 23–231, full-length recombinant mouse prion protein • PrP 90–231, truncated recombinant mouse prion protein • CJD, Creutzfeldt-Jakob disease • GSS, Gerstmann-Sträussler syndrome • FFI, fatal familial insomnia • BSE, bovine spongiform encephalopathy • GPI, glycosyl phosphatidylinositol • GdnHCl, guanidine hydrochloride • TfT, thioflavin T • CD, circular dichroism • AUC, analytical ultracentrifugation • n*, nucleus size
Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.051434005.
Reprint requests to: Jeffery Kelly, Department of Chemistry and Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road BCC-506, La Jolla, CA 92037, USA; e-mail: jkelly{at}scripps.edu; fax: (858) 784-9610.
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