Structure of γ-Secretase and Its Trimeric Pre-activation Intermediate by Single-particle Electron Microscopy

The gamma-secretase membrane protein complex is responsible for proteolytic maturation of signaling precursors and catalyzes the final step in the production of the amyloid beta-peptides implicated in the pathogenesis of Alzheimer disease. The incorporation of PEN-2 (presenilin enhancer 2) into a pre-activation intermediate, composed of the catalytic subunit presenilin and the accessory proteins APH-1 (anterior pharynx-defective 1) and nicastrin, triggers the endoproteolysis of presenilin and results in an active tetrameric gamma-secretase. We have determined the three-dimensional reconstruction of a mature and catalytically active gamma-secretase using single-particle cryo-electron microscopy. gamma-Secretase has a cup-like shape with a lateral belt of similar to 40-50 angstrom in height that encloses a water-accessible internal chamber. Active site labeling with a gold-coupled transition state analog inhibitor suggested that the gamma-secretase active site faces this chamber. Comparison with the structure of a trimeric pre-activation intermediate suggested that the incorporation of PEN-2 might contribute to the maturation of the active site architecture.