Sampling the conformational space of the catalytic subunit of human γ-secretase

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Medicine

Background:

• Human gamma-secretase (γ-secretase) is an intramembrane protease involved in cleaving substrates like Notch and amyloid precursor protein.
• Dysfunctional γ-secretase activity is linked to cancer and Alzheimer's disease.
• Previous cryo-electron microscopy (cryo-EM) structures showed disorder in the presenilin subunit.

Purpose of the Study:

• To characterize the molecular plasticity of γ-secretase at the secondary structure level.
• To identify distinct conformations of γ-secretase.
• To investigate the structural basis of substrate entry into the enzyme's active site.

Main Methods:

• Development of an image classification procedure for cryo-EM data.
• Analysis of γ-secretase structures to identify conformational states.
• Determination of a γ-secretase structure in complex with the inhibitor DAPT.

Main Results:

• Identified three distinct conformations of γ-secretase, revealing molecular plasticity.
• Observed an uncharacterized transmembrane helix in one conformation.
• Demonstrated that DAPT binding or the additional helix reduces conformational mobility in presenilin's transmembrane helices 2 and 6.

Conclusions:

• Presenilin's conformational mobility is modulated by inhibitor binding and an additional helix.
• These findings provide a new model for substrate translocation into the transmembrane domain of γ-secretase.
• Understanding γ-secretase conformations is crucial for developing therapeutics for associated diseases.