Generation of the amyloid-beta peptide N terminus in Saccharomyces cerevisiae expressing human Alzheimer's amyloid-beta precursor protein.

Abstract The Alzheimer's amyloid-β precursor protein (βAPP) is a type 1 membrane-spanning protein from which the Alzheimer's disease amyloid-β peptide (Aβ) is proteolytically derived. To date, attempts to identify the enzymes responsible for Aβ generation have failed. Here we report the accumulation of Aβ-immunoreactive peptides in yeast expressing human βAPP. Characterization of these peptides by metabolic labeling, immunoprecipitation with Aβ-specific antibodies, and N-terminal radiosequencing indicates that these peptides include the Aβ peptide at their N termini. The Aβ-like peptides generated in yeast were recovered predominantly as 8- and 12–14-kDa species. A 4-kDa species was recovered either when a protease-deficient strain was used to prevent breakdown or when the 8- and 12–14-kDa species were treated with disaggregating agents. The likely existence in yeast of enzymes generating the Aβ N terminus indicates that the molecular identification of yeast β-secretase-like enzymes may be accomplished using genetic screens or empirical approaches based upon the sequenced genome of Saccharomyces cerevisiae.