title: Two transmembrane aspartates in presenilin-1 required for presenilin endoproteolysis and gamma-secretase activity.
abstract: Accumulation of the amyloid-beta protein (Abeta) in the cerebral cortex is an early and invariant event in the pathogenesis of Alzheimer's disease. The final step in the generation of Abeta from the beta-amyloid precursor protein is an apparently intramembranous proteolysis by the elusive gamma-secretase(s). The most common cause of familial Alzheimer's disease is mutation of the genes encoding presenilins 1 and 2, which alters gamma-secretase activity to increase the production of the highly amyloidogenic Abeta42 isoform. Moreover, deletion of presenilin-1 in mice greatly reduces gamma-secretase activity, indicating that presenilin-1 mediates most of this proteolytic event. Here we report that mutation of either of two conserved transmembrane (TM) aspartate residues in presenilin-1, Asp 257 (in TM6) and Asp 385 (in TM7), substantially reduces Abeta production and increases the amounts of the carboxy-terminal fragments of beta-amyloid precursor protein that are the substrates of gamma-secretase. We observed these effects in three different cell lines as well as in cell-free microsomes. Either of the Asp --> Ala mutations also prevented the normal endoproteolysis of presenilin-1 in the TM6 --> TM7 cytoplasmic loop. In a functional presenilin-1 variant (carrying a deletion in exon 9) that is associated with familial Alzheimer's disease and which does not require this cleavage, the Asp 385 --> Ala mutation still inhibited gamma-secretase activity. Our results indicate that the two transmembrane aspartate residues are critical for both presenilin-1 endoproteolysis and gamma-secretase activity, and suggest that presenilin 1 is either a unique diaspartyl cofactor for gamma-secretase or is itself gamma-secretase, an autoactivated intramembranous aspartyl protease.
authors: Center for Neurologic Diseases, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts 02115, USA. mwolfe@utmem.edu
authors: M S
authors: MS
authors: Wolfe
authors: W
authors: W
authors: Xia
authors: B L
authors: BL
authors: Ostaszewski
authors: T S
authors: TS
authors: Diehl
authors: W T
authors: WT
authors: Kimberly
authors: D J
authors: DJ
authors: Selkoe
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D016466:CHO Cells; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D003067:Coenzymes / Q000378:metabolism; D006224:Cricetinae; D004563:Electrochemistry; D010450:Endopeptidases / Q000378:metabolism*; D005091:Exons; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000378:metabolism; D053764:Presenilin-1; D017510:Protein Folding; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D003067:Coenzymes; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D010446:Peptide Fragments; D053764:Presenilin-1; D011994:Recombinant Proteins; D001224:Aspartic Acid; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human