Employing a superior BACE1 cleavage sequence to probe cellular APP processing.
The involvement of beta-secretase (BACE1; beta-site APP-cleaving enzyme) in producing the beta-amyloid component of plaques found in the brains of Alzheimer's patients, has fueled a major research effort to characterize this protease. Here, we describe work toward understanding the substrate specificity of BACE1 that began by considering the natural APP substrate and its Swedish mutant, APPSw, and proceeded on to include oxidized insulin B chain and ubiquitin substrates. From these findings, and the study of additional synthetic peptides, we determined that a decapeptide derived from APP in which the P3-P2' sequence, ...VKM--DA..., was replaced by ...ISY--EV... (-- = beta site of cleavage), yielded a substrate that was cleaved by BACE1 seven times faster than the corresponding APPSw peptide, SEVNL--DAEFR. The expanded peptide, GLTNIKTEEISEISY--EVEFRWKK, was cleaved an additional seven times faster than its decapeptide counterpart (boldface), and provides a substrate allowing assay of BACE1 at picomolar concentrations. Several APP mutants reflecting these beta-site amino acid changes were prepared as the basis for cellular assays. The APPISYEV mutant proved to be a cellular substrate that was superior to APPSw. The assay based on APPISYEV is highly specific for measuring BACE1 activity in cells; its homolog, BACE2, barely cleaved APPISYEV at the beta-site. Insertion of the optimized ISY--EV motif at either the beta-site (Asp1) or beta'-site (Glu11) directs the rate of cellular processing of APP at these two accessible sites. Thus, we have identified optimal BACE1 substrates that will be useful to elucidate the cellular enzymatic actions of BACE1, and for design of inhibitors that might be of therapeutic benefit in Alzheimer's disease.
Tomasselli
Alfredo G
AG
Department of Protein Sciences, Pharmacia Corporation, 301 Henrietta Street, Kalamazoo, MI 49007, USA.
Qahwash
Isam
I
Emmons
Thomas L
TL
Lu
Yifeng
Y
Leone
Joseph W
JW
Lull
June M
JM
Fok
Kam F
KF
Bannow
Carol A
CA
Smith
Clark W
CW
Bienkowski
Michael J
MJ
Heinrikson
Robert L
RL
Yan
Riqiang
R
D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000502:physiology; D016466:CHO Cells; D006224:Cricetinae; D010450:Endopeptidases; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011499:Protein Processing, Post-Translational; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000502:physiology
D016564:Amyloid beta-Protein Precursor; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509284:BACE2 protein, human; C509280:BACE1 protein, human