Assembly of γ-secretase occurs through stable dimers after exit from the endoplasmic reticulum

gamma-Secretase affects many physiological processes through targeting >100 substrates; malfunctioning links.-secretase to cancer and Alzheimer's disease. The spatiotemporal regulation of its stoichiometric assembly remains unresolved. Fractionation, biochemical assays, and imaging support prior formation of stable dimers in the ER, which, after ER exit, assemble into full complexes. In vitro ER budding shows that none of the subunits is required for the exit of others. However, knockout of any subunit leads to the accumulation of incomplete subcomplexes in COPII vesicles. Mutating a DPE motif in presenilin 1 (PSEN1) abrogates ER exit of PSEN1 and PEN-2 but not nicastrin. We explain this by the preferential sorting of PSEN1 and nicastrin through Sec24A and Sec24C/D, respectively, arguing against full assembly before ER exit. Thus, dimeric subcomplexes aided by Sec24 paralog selectivity support a stepwise assembly of gamma-secretase, controlling final levels in postGolgi compartments.

Automated summary

gamma-secretase plays a role in various physiological processes by targeting over 100 substrates, with dysfunction linking it to cancer and Alzheimer's disease. The spatiotemporal regulation of its assembly remains unclear, but evidence suggests a stepwise process controlled by selective sorting mechanisms, leading to final levels in postGolgi compartments.