Nicastrin functions to sterically hinder γ-secretase-substrate interactions driven by substrate transmembrane domain
David M Bolduc1, Daniel R Montagna1, Yongli Gu1
1Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.
Summary
Gamma-secretase cleavage is driven by substrate transmembrane domains, not ectodomain interactions. Nicastrin acts as a gatekeeper, preventing larger substrates from binding to the gamma-secretase complex.
Area of Science:
- Biochemistry
- Molecular Biology
- Protease Function
Background:
- Gamma-secretase is an intramembrane-cleaving protease crucial for processing type-I integral membrane proteins.
- Substrate recognition and recruitment by gamma-secretase are poorly understood, with prior hypotheses involving ectodomain interactions with nicastrin.
- Understanding this mechanism is vital for comprehending protein processing and potential therapeutic interventions.
Purpose of the Study:
- To elucidate the mechanism by which gamma-secretase recognizes and binds its substrates.
- To investigate the role of the substrate's ectodomain and transmembrane domain in gamma-secretase binding and catalysis.
- To determine the function of the nicastrin component within the gamma-secretase complex regarding substrate selection.
Main Methods:
- Investigated substrate binding and cleavage by gamma-secretase using in vitro assays.
- Manipulated substrate ectodomain length and nicastrin structure to assess their impact on gamma-secretase activity.
- Compared the substrate binding mechanism of gamma-secretase to that of rhomboid proteases.
Main Results:
- Substrate ectodomain shedding is dispensable for gamma-secretase cleavage; binding is primarily driven by substrate transmembrane domains.
- Gamma-secretase-substrate interaction is distinct from the mechanism employed by rhomboid proteases.
- Disrupting the nicastrin fold enhances cleavage of substrates with longer ectodomains, suggesting nicastrin acts as a steric gatekeeper.
Conclusions:
- Gamma-secretase substrate recognition relies on transmembrane domain interactions, not ectodomain binding.
- Nicastrin functions as a molecular gatekeeper, regulating substrate access to the catalytic site through steric hindrance.
- This finding reframes the understanding of intramembrane protease substrate selection mechanisms.
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