Residues at P2-P1 positions of epsilon- and zeta-cleavage sites are important in formation of beta-amyloid peptide.

Most of the Alzheimer's disease (AD)-linked mutations in amyloid precursor protein (APP), which cause abnormal production of beta-amyloid (Abeta), are localized at the major beta-secretase-and gamma-secretase cleavage sites. In this study, using an APP-knockout mouse neuronal cell line, our data demonstrated that at the P2-P1 positions of the epsilon-cleavage site at Abeta49 and the zeta-cleavage site at Abeta46, aromatic amino acids caused a strong reduction in total Abeta. On the other hand, residues with a long side chain caused a decrease in Abeta(40) and a concomitant increase in Abeta(42) and Abeta(38). These findings indicate that the structures of the substituting residues at these key positions strongly determine the efficiency and preference of gamma-secretase-mediated APP processing, which determines the ratio of different secreted Abeta species, a crucial factor in the disease development. Our findings provide new insight into the mechanisms of gamma-secretase-mediated APP processing and, specifically, into why most AD-linked APP mutations are localized at major gamma-secretase cleavage sites. This information may contribute to the development of methods of prevention and treatment of Alzheimer's disease aimed at modulating gamma-secretase activity.