The dynamic conformational landscape of γ-secretase

The structure and function of the γ-secretase proteases are of vast interest because of their critical roles in cellular and disease processes. We established a novel purification protocol for γ-secretase complex that involves a conformation and complex-specific nanobody, yielding highly pure and active enzyme. Using single particle electron microscopy, we analyzed the γ-secretase structure and its conformational variability. Under steady state conditions the complex adopts three major conformations, which are different in overall compactness and relative position of the nicastrin ectodomain. Occupancy of the active or substrate binding sites by inhibitors differentially stabilize sub-populations of particles with compact conformations, whereas a Familial Alzheimer Disease-linked mutation results in enrichment of extended-conformation complexes with increased flexibility. Our study presents the γ-secretase complex as a dynamic population of inter-converting conformations, involving rearrangements at the nanometer scale and high level of structural interdependence between subunits. The fact that protease inhibition or clinical mutations, which affect Aβ generation, enrich for particular subpopulations of conformers indicates the functional relevance of the observed dynamic changes, which are likely instrumental for highly allosteric behavior of the enzyme.