Biochemical characterization of prions

Prion disease or transmissible spongiform encephalopathies are characterized by the presence of the abnormal form of the prion protein (PrP(Sc)). The pathological and transmissible properties of PrP(Sc) are enciphered in its secondary and tertiary structures. Since it's well established that different strains of prions are linked to different conformations of PrP(Sc), biochemical characterization of prions seems a preliminary but reliable approach to detect, analyze, and compare prion strains. Experimental biochemical procedures might be helpful in distinguishing PrP(Sc) physicochemical properties and include resistance to proteinase K (PK) digestion, insolubility in nonionic detergents, PK-resistance under denaturing conditions and sedimentation properties in sucrose gradients. This biochemical approach has been extensively applied in human prion disorders and subsequently expanded for PrP(Sc) characterization in animals. In particular, in sporadic Creutzfedlt-Jakob disease (sCJD) PrP(Sc) is characterized by two main glycotypes conventionally named Type 1 and Type 2, based on the apparent gel migration at 21 and 19kDa of the PrP(Sc) PK-resistant fragment. An additional PrP(Sc) type was identified in sCJD characterized by an unglycosylated dominant glycoform pattern and in 2010 a variably protease-sensitive prionopathy (VPSPr) was reported showing a PrP(Sc) with an electrophoretic ladder like pattern. Additionally, the presence of PrP(Sc) truncated fragments completes the electrophoretic characterization of different prion strains. By two-dimensional (2D) electrophoretic analysis additional PrP(Sc) pattern was identified, since this procedure provides information about the isoelectric point and the different peptides length related to PK cleavage, as well as to glycosylation extent or GPI anchor presence. We here provide and extensive review on PrP(Sc) biochemical analysis in human and animal prion disorders. Further, we show that PrP(Sc) glycotypes observed in CJD share similarities with PrP(Sc) in bovine spongiform encephalopathy forms (BSE).