Generation of amyloid β protein from its precursor is sequence specific

AbstractCerebral deposition of amyloid β protein (Aβ) is an early and critical feature of Alzheimer's disease. Here we analyze the substrate requirements of proteases (“β-secretases”) that cleave the R-amyloid precursor protein (βAPP) at the N-terminus of Aβ (Asp-597 of βAPP695)fis5) in intact human cells. The cleavage requires a membrane-bound substrate but tolerates shifts in the distance of the hydrolyzed bond from the membrane. The major protease has a minimum recognition region of Val-594 to Ala-598; most substitutions in this sequence strongly decrease or eliminate Aβ production. Only the Swedish familial Alzheimer's disease mutation (K595N/M596L) strongly increases AD production. Moreover, in this mutant but not in the wild type, the entire cytoplasmic tail with its reinternalization signals can be deleted without affecting Aβ N-terminal cleavage, consistent with the concept that cleavage of this mutant occurs in a different cellular compartment than that of wild-type molecules. Our results have important implications for current intensive approaches to develop assays for and identify enzymes with β-secretase activity