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

The Alzheimer's amyloid-beta precursor protein (beta APP) is a type 1 membrane-spanning protein from which the Alzheimer's disease amyloid-beta peptide (A beta) is proteolytically derived. To date, attempts to identify the enzymes responsible for A beta generation have failed. Here we report the accumulation of A beta-immunoreactive peptides in yeast expressing human beta APP. Characterization of these peptides by metabolic labeling, immunoprecipitation with A beta-specific antibodies, and N-terminal radiosequencing indicates that these peptides include the A beta peptide at their N termini. The A beta-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 A beta N terminus indicates that the molecular identification of yeast beta-secretase-like enzymes may be accomplished using genetic screens or empirical approaches based upon the sequenced genome of Saccharomyces cerevisiae.