Cooperative Roles of Hydrophilic Loop 1 and the C-Terminus of Presenilin 1 in the Substrate-Gating Mechanism of {gamma}-Secretase

-Secretase is a multisubunit protease complex that is responsible for generating amyloid-β peptides, which are associated with Alzheimer disease. The catalytic subunit of -secretase is presenilin 1 (PS1), which contains an initial substrate-binding site that is distinct from the catalytic site. Processive cleavage is suggested in the intramembrane-cleaving mechanism of -secretase. However, it largely remains unknown as to how -secretase recognizes its substrate during proteolysis. Here, we identified that the α-helical structural region of hydrophilic loop 1 (HL1) and the C-terminal region of human PS1 are distinct substrate-binding sites. Mutational analyses revealed that substrate binding to the HL1 region is critical for both - and -cleavage, whereas binding to the C-terminal region hampers -cleavage. Moreover, we propose that substrate binding triggers conformational changes in PS1, rendering it suitable for catalysis. Our data provide new insights into the complicated catalytic mechanism of PS1.