γ-Secretase Modulators and Inhibitors Induce Different Conformational Changes of Presenilin 1 Revealed by FLIM and FRET.

Elucidation of γ-secretase structure and dynamic conformational changes is of importance to drug discovery targeting this enzyme. Electron microscopy analyses provided important structural information, but the dynamic changes of γ-secretase in cells need to be explored further. We found that PS1 internal fluorescence resonance energy transfer (FRET) probes can incorporate into γ-secretase complex and possess secretase activity. Our results from fluorescence lifetime image microscopy (FLIM) and acceptor photobleaching FRET show different PS1 internal FRET when PS1 fluorescent probes expressed alone or with other secretase subunits Aph1aL, Nicastrin, and Pen2, indicating that PS1 internal FRET could be applied for probing conformational change of γ-secretase complex. Further, we accessed whether γ-secretase activity interfering compounds induced different conformational changes of PS1. Our results show that both γ-secretase modulators and inhibitors affect PS1 internal FRET but in different manners. These results demonstrate that FLIM and acceptor photobleaching FRET could be applied to monitor different PS1 conformational changes in γ-secretase.