Presenilin 1 is linked with gamma-secretase activity in the detergent solubilized state

gamma-Secretase is a membrane-associated protease that cleaves within the t ransmembrane region of amyloid precursor protein to generate the C termini of the two AP peptide isoforms, A beta 40 and A beta 42, Here we report the detergent solubilization and partial characterization of gamma-secretase. The activity of solubilized gamma-secretase was measured with a recombinant substrate, C100Flag, consisting largely of the C-terminal fragment of amyl oid precursor protein downstream of the beta-secretase cleavage site. Cleav age of C100Flag by gamma-secretase was detected by electrochemiluminescence using antibodies that specifically recognize the A beta 40 or A beta 42 te rmini. Incubation of C100Flag with HeLa cell membranes or detergent-solubil ized HeLa cell membranes generates both the A beta 40 and A beta 42 termini , Recovery of catalytically competent, soluble gamma-secretase critically d epends on the choice of detergent; CHAPSO (3-[(3-cholamidopropyl)dimethylam monio]-2-hydroxy-1-propanesulfonate) but not Triton X-100 is suitable, Solu bilized gamma-secretase activity is inhibited by pepstatin and more potentl y by a novel aspartyl protease transition-state analog inhibitor that block s formation of A beta 40 and A beta 42 in mammalian cells, Upon gel exclusi on chromatography, solubilized gamma-secretase activity coelutes with prese nilin 1 (PS1) at an apparent relative molecular weight of approximately 2.0 x 10(6). Anti-PS1 antibody immunoprecipitates gamma-secretase activity fro m the solubilized gamma-secretase preparation. These data suggest that gamm a-secretase activity is catalyzed by a PS1-containing macromolecular comple x.