Substrate Selection Criteria in Regulated Intramembrane Proteolysis.

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Alzheimer's disease is linked to amyloid-beta (Aβ) peptide deposits, formed by γ-secretase cleavage of APP.
• Understanding γ-secretase substrate recognition is vital, as current knowledge of how substrates enter the catalytic site is limited.
• The enzyme cleaves diverse substrates without a consensus sequence, yet mutations in transmembrane domains (TMDs) significantly alter cleavage efficiency.

Purpose of the Study:

• To investigate the structural and dynamic principles governing γ-secretase substrate recognition.
• To compare the TMDs of known γ-secretase substrates with nonsubstrates to identify distinguishing features.
• To elucidate the role of conformational flexibility and specific sequence motifs in substrate selection.

Main Methods:

• Review of existing 3D structures and dynamics of γ-secretase substrate TMDs.
• Analysis of mutant substrates with altered cleavage efficiencies.
• Presentation of structural and dynamic data for ITGB1, a γ-secretase nonsubstrate.
• Comparative biophysical analysis of TMDs from substrates and nonsubstrates.

Main Results:

• Identified three common motifs in γ-secretase substrates: a flexible TMD, a destabilized cleavage region, and a basic signature at the helix end.
• Conformational flexibility alone enhances cleavage efficiency for substrates like APP and Notch1.
• No single motif is exclusively required; rather, a variable combination determines substrate recognition.

Conclusions:

• Substrate recognition by γ-secretase is determined by a combination of factors, not just conformational flexibility.
• The identified motifs provide insights into the molecular basis of substrate specificity for this intramembrane protease.
• These findings contribute to understanding APP processing and potential therapeutic strategies for Alzheimer's disease.