Photo-induced crosslinking of prion protein oligomers and prions.

Prion diseases are caused by a unique type of infectious agent, which is thought to consist of a misfolded beta-sheeted form of the alpha-helical cellular prion protein (PrP(C)). This misfolded isoform (PrP(Sc)) tends to form insoluble amyloid-like aggregates, impeding classical structural analysis by X-ray crystallography or NMR. Intermolecular crosslinking may provide a means of stabilizing notoriously elusive oligomers for further analysis and may be used for analyzing aggregate architecture by characterising intermolecular contact sites. Using a photo-induced crosslinking method (PICUP), aggregates of recombinant PrP (rPrP) and PrP(Sc) were linked at interacting surfaces via amino acid side chains. The degree of crosslinking within PrP aggregates was adjustable using varying light intensities and could efficiently be monitored by fluorescence correlation spectroscopy. Specific intermolecular crosslinking of PrP(Sc) molecules was achieved even in crude brain homogenate. Functional studies showed that stabilized aggregates of rPrP did not loose their capacity to induce further protein aggregation and crosslinking of PrP(Sc) did not alter significantly the level of infectivity, indicating that photo-induced covalent linkage of PrP(Sc) does not destruct surfaces important for prion propagation.