Evidence that enzyme processivity mediates differential Aβ production by PS1 and PS2

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• The γ-secretase complex, composed of presenilin-1 (PS1) or presenilin-2 (PS2) subunits, cleaves amyloid precursor protein (APP).
• PS1-containing γ-secretase complexes are known to generate more total amyloid-β (Aβ) than PS2-containing complexes.
• The cleavage activity at the APP ε-site, producing the APP intracellular domain (AICD), has not been directly compared between PS1 and PS2.

Purpose of the Study:

• To investigate whether PS1 and PS2 exhibit differential cleavage activity at the APP ε-site, analogous to their known differential activity at the APP γ-site.
• To compare the production of AICD generated by PS1-containing versus PS2-containing γ-secretase complexes.
• To assess the impact of PS1 and PS2 on Notch intracellular domain (NICD) production as a related measure of cleavage activity.

Main Methods:

• Utilized a novel Swedish APP-GVP substrate for parallel detection of Aβ and AICD.
• Employed PS1-/-/PS2-/- cells co-transfected with either PS1 or PS2.
• Quantified Aβ, AICD, and NICD production to assess γ-secretase activity.

Main Results:

• PS1-containing complexes generated more total Aβ than PS2-containing complexes, confirming previous findings.
• Unexpectedly, PS1 and PS2 generated equal amounts of AICD product.
• PS1 and PS2 also produced equivalent amounts of NICD, indicating similar cleavage activity at the Notch S3-site.

Conclusions:

• PS1 and PS2 exhibit differential activity in Aβ production but equivalent activity in AICD and NICD production.
• Processivity differences between PS1 and PS2 likely explain the differential production of Aβ peptide.
• These findings provide novel insights into γ-secretase biology and have implications for therapeutic strategies targeting this complex.