Mechanisms of γ-Secretase Activation and Substrate Processing

Area of Science:

• Biochemistry
• Computational Biology
• Neuroscience

Background:

• Alzheimer's disease (AD) is characterized by amyloid plaques, primarily composed of amyloid β-peptide.
• Amyloid β-peptide is generated by the intramembrane proteolysis of amyloid precursor protein (APP) via γ-secretase.
• The precise mechanisms of γ-secretase-mediated intramembrane proteolysis and substrate processing are not fully understood.

Purpose of the Study:

• To investigate the mechanisms of γ-secretase substrate processing for both wildtype and mutant amyloid precursor protein (APP).
• To combine all-atom simulations with biochemical experiments to elucidate enzyme activation and cleavage site dynamics.

Main Methods:

• Utilized Gaussian accelerated molecular dynamics (GaMD) simulations for all-atom modeling.
• Performed complementary biochemical experiments, including mass spectrometry and Western blotting.
• Analyzed distinct low-energy conformational states, substrate secondary structures, and active-site subpockets.

Main Results:

• GaMD simulations captured spontaneous γ-secretase activation, with key catalytic residues and water molecules positioned for APP proteolysis at the ε cleavage site.
• Familial AD mutations I45F and T48P were shown to enhance initial ε cleavage, while the M51F mutation shifted the cleavage site.
• Simulation findings on enzyme states, substrate structures, and active-site interactions were consistent with experimental results.

Conclusions:

• The study successfully elucidated the mechanisms of γ-secretase activation and APP substrate processing using a combined simulation and experimental approach.
• Findings provide crucial insights into how familial AD mutations affect γ-secretase activity.
• This work lays the foundation for rational computer-aided drug design targeting γ-secretase for Alzheimer's disease therapy.