Extracellular interface between APP and Nicastrin regulates Aβ length and response to γ‐secretase modulators

Abstract

γ‐Secretase complexes ( GSEC s) are multimeric membrane proteases involved in a variety of physiological processes and linked to Alzheimer's disease ( AD ). Presenilin ( PSEN , catalytic subunit), Nicastrin ( NCT ), Presenilin Enhancer 2 ( PEN ‐2), and Anterior Pharynx Defective 1 ( APH 1) are the essential subunits of GSEC s. Mutations in PSEN and the Amyloid Precursor Protein ( APP ) cause early‐onset AD . GSEC s successively cut APP to generate amyloid‐β (Aβ) peptides of various lengths. AD ‐causing mutations destabilize GSEC ‐ APP /Aβ n interactions and thus enhance the production of longer Aβs, which elicit neurotoxic events underlying pathogenesis. Here, we investigated the molecular strategies that anchor GSEC and APP /Aβ n during the sequential proteolysis. Our studies reveal that a direct interaction between NCT ectodomain and APP C99 influences the stability of GSEC ‐Aβn assemblies and thereby modulates Aβ length. The data suggest a potential link between single‐nucleotide variants in NCSTN and AD risk. Furthermore, our work indicates that an extracellular interface between the protease ( NCT , PSEN ) and the substrate ( APP ) represents the target for compounds ( GSM s) modulating Aβ length. Our findings may guide future rationale‐based drug discovery efforts.

Aβ43‐producing PS1 FAD mutants cause altered substrate interactions and respond to γ‐secretase modulation

“…The resulting longer substrate residence time would thereby allow more efficient carboxy-terminal processing toward shorter Ab species. As shown very recently, these effects relate functionally to the proximity of K28 to NCT [36,43] and indicate this contact region with C99 and/or Ab also as part of a GSM binding site [44]. As shown very recently, these effects relate functionally to the proximity of K28 to NCT [36,43] and indicate this contact region with C99 and/or Ab also as part of a GSM binding site [44].…”

Side-by-side comparison of Notch- and C83 binding to γ-secretase in a complete membrane model at physiological temperature

“…The RMSF of NCT-ECD in gsecretase-C83 displayed several high peaks as expected and discussed above, whereas the region Phe240-Glu245, which interacts with the extracellular part of C83, displayed small uctuations (1.3-1.6 A). NCT-ECD motions are important because they likely affect the dynamic stability of g-secretase-Ab assemblies and thereby modulate Ab length, 105 and some gsecretase modulators tend to bind at the extracellular interface between NCT and PS1. 106 The dynamics of Ser241 and Ile242 in the proximity of NCT interacting with Lys12 of C83 (corresponding to Lys699 in APP) were explored by measuring the minimum distance between these residues (Fig.…”

“…S6 †), which interacts with the TM of APP. 105,107 The binding induces a conformational change in PS1. 108 Unlike PS1 fAD mutations, g-secretase modulators probably increase the stability of the g-secretase-Ab complex and decrease the premature dissociation of Ab, which results in additional trimming of the substrate.…”

“…8) provide a possibility that this part of NCT affects the stability of the enzymesubstrate complex which in turn would modulate the Ab length, according to the FIST model 80,121 and experimental evidence. 105 To understand the energetic difference in substrate recognition, we computed the binding free energy for both complexes, using the equilibrated snapshots from the last 300 ns, with the MM/PBSA approach (Table S5 †). We found that the energetic contributions from different components of Notch and C83 were similar in nature.…”

Mechanisms of γ-Secretase Activation and Substrate Processing

“…Computational modeling, especially molecular dynamics (MD) simulation, has proven useful in understanding the structural dynamics of γ -secretase. Previous studies have provided valuable insights into the conformational changes [15][16][17][18] , enzyme allosteric modulation 19 , substrate binding 15,18,[20][21][22] , water distribution [15][16] , lipid interactions 16 and ligand binding of γ -secretase [23][24][25] .…”