PS1 N- and C-terminal fragments form a complex that functions in APP processing and Notch signaling

Area of Science:

• Molecular biology
• Neuroscience
• Biochemistry

Background:

• Presenilin proteins are key in cleaving Notch and amyloid precursor protein (APP).
• Presenilin undergoes endoproteolytic processing into N-terminal (NTF) and C-terminal (CTF) fragments.
• Previous studies showed overexpression of full-length presenilin 1 (PS1) does not alter NTF and CTF levels.

Purpose of the Study:

• To determine the active species of presenilin.
• To investigate the role of PS1 NTF and CTF in gamma-secretase activity.
• To elucidate the mechanism by which specific PS1 mutations affect amyloid-beta (Abeta) production.

Main Methods:

• Coexpression of PS1 NTF and CTF in cells.
• Analysis of cellular fragment levels.
• Assessment of gamma-secretase activity in cells with wild-type and mutated PS1.

Main Results:

• Coexpression of PS1 NTF and CTF significantly increases their cellular levels.
• A noncovalent complex of PS1 NTF and CTF was identified as the active presenilin species.
• This complex is necessary but not sufficient for gamma-secretase activity.
• Specific mutations (Asp-257 and Asp-385) directly impair gamma-secretase activity, not PS1 processing.

Conclusions:

• The PS1 NTF/CTF complex is the functional unit of presenilin, essential for gamma-secretase activity.
• Mutations affecting gamma-secretase activity directly impact the enzyme's function rather than presenilin processing.
• This research clarifies the molecular basis of presenilin function in APP metabolism and Abeta generation.