Monitoring Prion Protein Stability by NMR

Abstract

Prion diseases, or transmissible spongiform encephalopathies (TSE), are a group of fatal neurological diseases that affect both humans and animals. At the end of the 20th century, bovine spongiform encephalopathy (BSE), better known as mad cow disease, was shown to be transmissible to humans. This resulted in considerable concern for public health and a number of questions for scientists. The first question answered was the possible source of the disease, which appears to be the prion protein (PrP). There are two major forms of this protein: the native, noninfectious form (PrP^C), and the misfolded infectious form (PrP^Sc). PrP^C is mainly α-helical in structure, whereas PrP^Sc aggregates into an assembly of β-sheets, forming amyloid fibrils. Since the first solution structure of the noninfectious form of the mouse prion protein, about 30 structures of the globular portion of PrP^C have been characterized from different organisms. However, only a few minor differences are observed when comparing one PrP^C structure to another. The key to understanding prion formation may then be not in the structure of PrP^C, but in the mechanism underlying PrP^C unfolding and then conversion into a misfolded fibril state. To identify the possible region(s) of PrP^C responsible for initiating the conversion into the amyloid fibril formation, nuclear magnetic resonance (NMR) was applied to characterize the stability and structure of PrP^C and intermediate states during the conversion from PrP^C to PrP^Sc. Subsequently urea was used to induce unfolding, and data analysis revealed region-specific structural stabilities that may bring insights into the mechanisms underlying conversion of protein into an infectious prion.

Acknowledgements

The authors are grateful to Dr. Subhrangsu Chatterjee for many helpful discussions. The authors thank Angela Thiessen, Elia Fong, and Christa Chisholm (University of Guelph) for the protein expression and purification, and Ryan McKay (NANUC) for help with spectra acquisition. This work was supported by the Alberta Prion Research Institute, operated by Alberta Ingenuity, and PrioNet Canada funded from the Networks of Centres of excellence Canada program. We thank the Canadian National High Field NMR Centre (NANUC) for its assistance and use of its facilities, and the Canadian Institutes of Health Research (CIHR), the Natural Science and Engineering Research Council of Canada (NSERC), and the University of Alberta Heritage Fund for operation of NANUC. O. Julien is a recipient of an Alberta Heritage Foundation for Medical Research studentship and a Frederick Banting and Charles Best Canada Graduate Scholarship from CIHR.