Partial Purification and Characterization of -Secretase from Post-mortem Human Brain*

One characteristic feature of Alzheimer’s disease is the deposition of amyloid -peptide (A ) as amyloid plaques within specific regions of the human brain. A is derived from the amyloid -peptide precursor protein ( -APP) by the intramembranous cleavage activity of -secretase. Studies in cells have revealed that -secretase is a large multimeric membrane-bound protein complex that is functionally dependent on several proteins, including presenilin, nicastrin, Aph-1, and Pen-2. However, the precise biochemical and molecular nature of -secretase is as yet to be fully elucidated, and no investigations have analyzed -secretase in human brain. To address this we have developed a novel in vitro -secretase activity assay using detergent-solubilized cell membranes and a -APP-derived fluorescent probe. We report that human brain-derived -secretase activity co-purifies with a high molecular weight protein complex comprising presenilin, nicastrin, Aph-1, and Pen-2. The inhibitor profile and solubility characteristics of brain-derived -secretase are similar to those described in cells, and proteolysis occurs at the A and A generating cleavage sites. The ability to isolate -secretase from post-mortem human brain may facilitate the identification of brain-specific modulators of -APP processing and provide new insights into the biology of this important factor in the pathogenesis of Alzheimer’s disease.