Abstract
Cerebral deposition of amyloid beta-protein (A beta) is believed to play a key role in the pathogenesis of Alzheimer's disease. Because A beta is produced from the processing of amyloid beta-protein precursor (APP) by beta- and gamma-secretases, these enzymes are considered important therapeutic targets for identification of drugs to treat Alzheimer's disease. Unlike beta-secretase, which is a monomeric aspartyl protease, gamma-secretase activity resides as part of a membrane-bound, high molecular weight, macromolecular complex. Pepstatin and L685458 are among several structural classes of gamma-secretase inhibitors identified so far. These compounds possess a hydroxyethylene dipeptide isostere of aspartyl protease transition state analogs, suggesting gamma-secretase may be an aspartyl protease. However, the mechanism of inhibition of gamma-secretase by pepstatin and L685458 has not been elucidated. In this study, we report that pepstatin A methylester and L685458 unexpectedly displayed linear non-competitive inhibition of gamma-secretase. Sulfonamides and benzodiazepines, which do not resemble transition state analogs of aspartyl proteases, also displayed potent, non-competitive inhibition of gamma-secretase. Models to rationalize how transition state analogs inhibit their targets by non-competitive inhibition are discussed.
Highlights
Non-competitive Inhibition of ␥-Secretase by L685458, Sulfonamides, and Benzodiazepines—To determine whether this type of non-competitive inhibition is PME-specific, we investigated the inhibition kinetics for three other types of ␥-secretase inhibitors
The simplest interpretation of the linear non-competitive inhibition by PME is that PME binds to a non-catalytic, allosteric site of ␥-secretase, which can be adequately described by a simple kinetic scheme as shown by Equation 7
It is known that ␥-secretase is a high molecular weight, macromolecular complex [13, 14]. This complex contains at least two functional units, presenilin (1 or 2) and nicastrin [13]
Summary
A, -amyloid; APP, amyloid precursor protein; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate; CHAPSO, 2-hydoxy-CHAPS; CTF, C-terminal fragment of presenilin; CTF␣, CTF of ␣-secretase-cleaved APP (C83); CTF, CTF fragment of -secretase-cleaved APP (C99); NTF, N-terminal fragment of presenilin; PME, pepstatin A methylester; PS, presenilin; RAA40, rabbit anti-A40; MES, 4-morpholineethanesulfonic acid. Recent pepstatin-derived affinity chromatography of PS1 [23], photo affinity labeling of PS1 with transition state analog L685458 [12], and chemical affinity labeling of PS1 with difluoro peptidomimetics [24] further support ␥-secretase as an aspartyl protease and have led to the tentative identification of presenilins as the catalytic components of ␥-secretase. These transition state analogs have been extensively used as tools to probe the structure and mechanism, as well as the biochemical and cellular functions, of ␥-secretase, the mechanisms of ␥-secretase inhibition by these compounds have not been elucidated. A number of theoretical models are discussed in an attempt to rationalize this phenomenon
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
