title: Identification of a beta-secretase activity, which truncates amyloid beta-peptide after its presenilin-dependent generation.
abstract: The beta-amyloid precursor protein (beta APP) is proteolytically processed by two secretase activities to produce the pathogenic amyloid beta-peptide (A beta). N-terminal cleavage is mediated by beta-secretase (BACE) whereas C-terminal intramembraneous cleavage is exerted by the presenilin (PS) gamma-secretase complex. The A beta-generating gamma-secretase cleavage principally occurs after amino acid 40 or 42 and results in secretion of A beta-(1-40) or A beta-(1-42). Upon overexpression of BACE in cultured cells we unexpectedly noticed a reduction of secreted A beta-(1-40/42). However, mass spectrometry revealed a truncated A beta species, which terminates at amino acid 34 (A beta-(1-34)) suggesting an alternative gamma-secretase cut. Indeed, expression of a loss-of-function variant of PS1 inhibited not only the production of A beta-(1-40) and A beta-(1-42) but also that of A beta-(1-34). However, expression levels of BACE correlate with the amount of A beta-(1-34), and A beta-(1-34) is produced at the expense of A beta-(1-40) and A beta-(1-42). Since this suggested that BACE is involved in a C-terminal truncation of A beta, we incubated purified BACE with A beta-(1-40) in vitro. Under these conditions A beta-(1-34) was generated. Moreover, when conditioned media containing Abeta-(1-40) and A beta-(1-42) were incubated with cells expressing a loss-of-function PS1 variant together with BACE, A beta-(1-34) was efficiently produced in vivo. These data demonstrate that an apparently gamma-secretase-dependent A beta derivative is produced after the generation of the non-truncated A beta via an additional and unexpected activity of BACE.
authors.affiliation: Adolf-Butenandt Institute, Department of Biochemistry, Laboratory for Alzheimer's and Parkinson's Disease Research, Schillerstrasse 44, Ludwig-Maximilians University, 80336 Munich, Germany.
authors.forename: Regina
authors.initials: R
authors.lastname: Fluhrer
authors.forename: Gerd
authors.initials: G
authors.lastname: Multhaup
authors.forename: Andrea
authors.initials: A
authors.lastname: Schlicksupp
authors.forename: Masayasu
authors.initials: M
authors.lastname: Okochi
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Takeda
authors.forename: Sven
authors.initials: S
authors.lastname: Lammich
authors.forename: Michael
authors.initials: M
authors.lastname: Willem
authors.forename: Gil
authors.initials: G
authors.lastname: Westmeyer
authors.forename: Wolfram
authors.initials: W
authors.lastname: Bode
authors.forename: Jochen
authors.initials: J
authors.lastname: Walter
authors.forename: Christian
authors.initials: C
authors.lastname: Haass
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D010450:Endopeptidases / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D053764:Presenilin-1; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection
chemical_list: D016564:Amyloid beta-Protein Precursor; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D053764:Presenilin-1; D011994:Recombinant Proteins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509284:BACE2 protein, human; C509280:BACE1 protein, human