Presenilin-1 and presenilin-2 exhibit distinct yet overlapping gamma-secretase activities.
Presenilin-1 (PS1) and presenilin 2 (PS2) are proposed to be transmembrane aspartyl proteases that cleave amyloid precursor protein and Notch. PS1- and PS2-mediated activities were individually characterized using blastocyst-derived (BD) cells and membranes from PS1+/--PS2-/- and PS1-/-PS2+/+ mice, respectively. The relative amounts of PS1 and PS2 in the various BD cells were determined from the intensities of the anti-PS1 and anti-PS2 immunoblot signals by comparison with standard curves using radiolabeled PS1 and PS2 standards produced by in vitro transcription and translation. Cellular membranes from wild type, PS1-/-PS2+/+, and PS1+/--PS2-/- but not PS1-/-PS2-/- BD cells generated the Abeta40 and Abeta42 products from the C100FLAG substrate. PS1-associated gamma-secretase displays considerably higher specific activity than PS2-associated gamma-secretase. Moreover, the PS1+/-PS2-/- BD cells and corresponding membranes exhibited much higher gamma-secretase activity as compared with other BD cells and membranes. The PS1-mediated gamma-secretase activity correlated better with the amount of PS1 that is modifiable by a photoactivated active site-directed gamma-secretase inhibitor rather than total PS1; hence, only a small portion (<14%) of the PS1 in wild-type membranes appears to be engaged in an active gamma-secretase complex. This finding suggests that PS1 may serve other biological functions in addition to that associated with its gamma-secretase activity. Furthermore, the PS1 gamma-secretase complex and the PS2 gamma-secretase complex activities can be discriminated on the basis of their susceptibility to inhibition by a potent gamma-secretase inhibitor. The distinct yet overlapping enzymatic properties of the PS1 gamma-secretase complex and the PS2 gamma-secretase complex imply that these two putative aspartyl class proteases may contribute to different biological processes.
Lai
Ming-Tain
MT
Department of Biological Chemistry, Merck Research Laboratories, West Point, Pennsylvania 19486, USA. mingtain_lai@merck.com
Chen
Elizabeth
E
Crouthamel
Ming-Chih
MC
DiMuzio-Mower
Jillian
J
Xu
Min
M
Huang
Qian
Q
Price
Eric
E
Register
R Bruce
RB
Shi
Xiao-Ping
XP
Donoviel
Dorit B
DB
Bernstein
Alan
A
Hazuda
Daria
D
Gardell
Stephen J
SJ
Li
Yue-Ming
YM
D000345:Affinity Labels; D000544:Alzheimer Disease; D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D001755:Blastocyst / Q000201:enzymology; D002462:Cell Membrane / Q000201:enzymology; D003001:Cloning, Molecular; D010450:Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D053764:Presenilin-1; D053766:Presenilin-2; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
D000345:Affinity Labels; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D053764:Presenilin-1; D053766:Presenilin-2; D011994:Recombinant Proteins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse