The Involvement of C-Terminal Amino Acids in the Formation of Prion Protein Dimers
Accumulations o f abnormal prion protein are thought to be the cause o f the transmissible spongiform encephalopathies, which are degenerative brain diseases. Throughout the disease process it is hypothesized that there is some sort of binding that occurs among the proteins. This research project involved the search for a strong, most likely covalent, linkage in a dimer of prion proteins. The focus was on the amino acid sequence o f the prion protein from 220 to 232. The lysine residue in this sequence was of particular concern due to its involvement in covalent linkages in other proteins (Priola et al., 1995; Reiser et al., 1992). The following amino acid deletions were made to determine if their absence resulted in a loss of binding between the segments o f amino acids o f two proteins: Lys, Glu, Ser, Lys/Glu, and Glu/Ser at positions 220, 221, 222, 220/222, and 221/222, respectively. It was hypothesized that the mutant with lysine deleted from its sequence would not be involved in dimer formation. However, an SDSpolyacrylamide gel electrophoresis of these mutant proteins indicated dark bands at approximately 60 kDa, the size o f two linked 30 kDa prion proteins, indicating that all the proteins were still able to dimerize. Therefore, the binding site o f two molecules of prion protein must involve other amino acids.