ABSTRACT
Because production and deposition of the amyloid-ß peptide (Aß) is intimately linked to the pathogenesis of Alzheimer’s disease (AD), the proteases responsible for excising Aß from the amyloid-ß precursor protein (APP), ß-and γ-secretases, are considered im portant therapeutic targets, ß-secretase is a membrane-anchored aspartyl protease in the pepsin family. In contrast, γ-secretase is a highly complex and unusual protease that catalyzes hydroly sis within the transmembrane domain of its substrates. A large body of evidence now supports the hypothesis that the catalytic component of γ-secretase is presenilin, a multi-pass membrane protein. Genetic analysis identified presenilins as major loci for mutations that cause familial, early onset AD. These mutations affect Aß production by altering the specificity of γ-secretase, and knockout of presenilins eliminates γ-secretase activity. The identification of transition-state analogue inhibitors of γ-secretase suggested an aspartyl protease mechanism. Consistent with all these findings, two conserved transmembrane aspartates in presenilin are critical for γ-secretase activity, and active site directed inhibitors of γ-secretase bind directly to presenilin. Moreover, presenilin copurifies with γ-secretase activity through size exclusion and affinity chromatogra phy, and antibodies to presenilin can precipitate γ-secretase activity. Presenilins by themselves do not possess protease activity. Instead, presenilins are apparently part of a larger protease complex that includes the single-pass protein nicastrin and at least two other components.
