ABSTRACT
Beta amyloid peptides (Aß) play a key role in the pathogenesis of Alzheimer disease (AD). Presenilins (PS) function as the catalytic subunits of γ-secretase, the enzyme that releases Aß from ectodomain cleaved amyloid precursor protein (APP) by intramembrane proteolysis. Familial Alzheimer disease (FAD)-linked PSEN mutations alter APP processing in a manner that increases the relative abundance of longer Aß42 peptides to that of Aß40 peptides. The mechanisms by which Aß40 and Aß42 peptides are produced in a ratio of ten to one by wild type presenilin (PS) and by which Aß42 is overproduced by FAD-linked PS variants are not completely understood. We generated chimeras of the amyloid precursor protein C-terminal fragment (C99) and PS to address this issue. We found a chimeric protein where C99 is fused to the PS1 N-terminus undergoes in cis processing to produce Aß and that a fusion protein harboring FAD-linked PS1 mutations overproduced Aß42. To change the molecular interactions within the C99-PS1 fusion protein, we made sequential deletions of the junction between C99 and PS1. We found differential effects of deletion in C99-PS1 on Aß40 and 42 production. Deletion of the junction between APP CTF and PS1 in the fusion protein decreased Aß40, while it did not decrease Aß42 production in the presence or absence of FAD-linked PS1 mutation. These results are consistent with the idea that the APP/PS interaction is differentially regulated during Aß40 and 42 production.
