Allosteric Modulation of PS1/γ-Secretase Conformation Correlates with Amyloid β42/40 Ratio

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Abstract
Presenilin 1(PS1) is the catalytic subunit of γ-secretase, the enzyme responsible for the Aβ C-terminal cleavage site, which results in the production of Aβ peptides of various lengths. Production of longer forms of the Aβ peptide occur in patients with autosomal dominant Alzheimer disease (AD) due to mutations in presenilin. Many modulators of γ-secretase function have been described. We hypothesize that these modulators act by a common mechanism by allosterically modifying the structure of presenilin. To test this hypothesis we generated a genetically encoded GFP-PS1-RFP (G-PS1-R) FRET probe that allows monitoring of the conformation of the PS1 molecule in its native environment in live cells. We show that G-PS1-R can be incorporated into the γ-secretase complex, reconstituting its activity in PS1/2 deficient cells. Using Förster resonance energy transfer (FRET)-based approaches we show that various pharmacological and genetic manipulations that target either γ-secretase components (PS1, Pen2, Aph1) or γ-secretase substrate (amyloid precursor protein, APP) and are known to change Aβ42 production are associated with a consistent conformational change in PS1. These results strongly support the hypothesis that allosteric changes in PS1 conformation underlie changes in the Aβ42/40 ratio. Direct measurement of physiological and pathological changes in the conformation of PS1/γ-secretase may provide insight into molecular mechanism of Aβ42 generation, which could be exploited therapeutically.

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