Substrate docking to γ-secretase allows access of γ-secretase modulators to an allosteric site

Abstract

γ-Secretase generates the peptides of Alzheimer's disease, Aβ40 and Aβ42, by cleaving the amyloid precursor protein within its transmembrane domain. γ-Secretase also cleaves numerous other substrates, raising concerns about γ-secretase inhibitor off-target effects. Another important class of drugs, γ-secretase modulators, alter the cleavage site of γ-secretase on amyloid precursor protein, changing the Aβ42/Aβ40 ratio, and are thus a promising therapeutic approach for Alzheimer's disease. However, the target for γ-secretase modulators is uncertain, with some data suggesting that they function on γ-secretase, whereas others support their binding to the amyloid precursor. In this paper we address this controversy by using a fluorescence resonance energy transfer-based assay to examine whether γ-secretase modulators alter Presenilin-1/γ-secretase conformation in intact cells in the absence of its natural substrates such as amyloid precursor protein and Notch. We report that the γ-secretase allosteric site is located within the γ-secretase complex, but substrate docking is needed for γ-secretase modulators to access this site.

γ-Secretase Modulator (GSM) Photoaffinity Probes Reveal Distinct Allosteric Binding Sites on Presenilin

“…Additionally, we made the surprising observation that the labeling of E2012-BPyne to PS1-NTF is enhanced in the presence of very low concentrations of the active site-directed GSI L458, suggesting a degree of cooperativity between the ␥-secretase active site and the GSM binding site(s). Although we did not observe any significant difference in the ability of E2012-BPyne to bind and label PS1-NTF in cells overexpressing wild type APP, it is possible that various ␥-secretase substrates could also influence specific GSM binding sites, and this is an important area for further investigation (51,52). In summary, these results support the hypothesis that multiple binding sites exist within the ␥-secretase complex, each of which contribute to different modes of modulatory or inhibitory action.…”

Allosteric regulation of γ-secretase activity by a phenylimidazole-type γ-secretase modulator

“…3D). In contrast, helical peptide enabled ibuprofen and fenofibrate to alter the conformation of PS1 (40). Notably, we have reported that acidic-type GSMs target TM1 (24,41).…”

Alzheimer’s disease mutations in APP but not γ-secretase modulators affect epsilon-cleavage-dependent AICD production

“…The complex contains a total of 19 a-helices embedded in the membrane bilayer, which allows the overall structure to adopt different conformations upon binding with the substrate or different chemical compounds 9,10 . Moreover, the catalytic aspartate residues (Asp257/385) in hPS1 are buried into the lipid bilayer and surrounded by hydrophobic helices and the electron microscopy density maps suggested the existence of two pores in the globular structure of g-secretase, which can explain the entrance of water molecules necessary for the hydrolysis of the peptide bond 11 .…”