Purification and cloning of amyloid precursor protein beta-secretase from human brain

Proteolytic processing of the amyloid precursor protein (APP) generates amy loid beta (A beta) peptide, which is thought to be causal for the pathology and subsequent cognitive decline in Alzheimer's disease. Cleavage by beta- secretase at the amino terminus of the A beta peptide sequence, between res idues 671 and 672 of APP, leads to the generation and extracellular release of beta-cleaved soluble APP(1), and a corresponding cell-associated carbox y-terminal fragment. Cleavage of the C-terminal fragment by gamma-secretase (s) leads to the formation of A beta. The pathogenic mutation K670M671 --> N670L671 at the beta-secretase cleavage site in APP(2), which was discovere d in a Swedish family with familial Alzheimer's disease, leads to increased beta-secretase cleavage of the mutant substrate(3). Here we describe a mem brane-bound enzyme activity that cleaves full-length APP at the beta-secret ase cleavage site, and find it to be the predominant beta-cleavage activity in human brain. We have purified this enzyme activity to homogeneity from human brain using a new substrate analogue inhibitor of the enzyme activity , and show that the purified enzyme has all the properties predicted for be ta-secretase. Cloning and expression of the enzyme reveals that human brain beta-secretase is a new membrane-bound aspartic proteinase.