Human PrP primary structure. (a) Schematic diagram of human PrP primary structure showing the location of epitopes for the MAR-1 capture antibody (used in CDI) and the 3F4 detection antibody (used in CDI and western blotting) and the regions corresponding to the 18-30 kDa PrPres bands and the ~8 kDa PrPres band. Blue circles indicate the position of the glycan moieties at amino acids 181 and 197. Note that MAR-1 epitope is discontinuous and depends on an intact C-terminal disulphide bond, which is absent from the ~8 kDa PrPres fragment seen in cases of VPSPr. Due to the position of the MAR-1 capture epitope, only PrPSc with an intact C-terminus is detectable by CDI. (b) Schematic diagram indicating the approximate migration positions of bands obtained when samples from sCJD brain or VPSPr brain are treated with PK and analysed by immunoblotting using the anti-PrP monoclonal antibody 3F4 (epitope amino acids 106-112). The upper ~19 and ~23 kDa bands observed in some VPSPr cases have mobilities similar the unglycosylated and monoglycosylated bands of type 2A PrPres in sCJD.