Fig. 2. Prion protein isoforms. (A) Western immunoblot of brain homogenates from uninfected (lanes 1 and 2) and prion-infected (lanes 3 and 4) SHa. Samples in lanes 2 and 4 were digested with 50 µg/ml proteinase K for 30 min at 37°C. PrPC in lanes 2 and 4 was completely hydrolyzed under these conditions, whereas approximately 67 amino acids were digested from the NH2 terminus of PrPSc to generate PrP 27-30. After polyacrylamide gel electrophoresis (PAGE) and electrotransfer, the blot was developed with anti-PrP R073 polyclonal rabbit antiserum. Molecular size markers are in kilodaltons (kDa). (B) Bar diagram of SHaPrP, which consists of 254 amino acids. Attached carbohydrate (CHO) and a glycosyl-phosphatidylinositol (GPI) anchor are indicated. After processing of the NH2 and COOH termini, both PrPC and PrPSc consist of 209 residues. After limited proteolysis, the NH2 terminus of PrPSc is truncated to form PrP 27-30, which is composed of approximately 142 amino acids.
From: S. B. Prusiner (1998) Prions. Proc. Natl. Acad. Sci. USA 95: 13363-13383 (html)(pdf)