M28 Zn-peptidase nicastrin, a main component of gamma-secretase complex
Peptidase M28 family, nicastrin subfamily. Nicastrin is a main component of the gamma-secretase complex, which also contains presenilin, Pen-2 and Aph-1. Its extracellular domain sequence resembles aminopeptidases, but certain catalytic residues are not conserved. It is mainly localized to the endoplasmic reticulum and Golgi. It is highly glycosylated (Mr 120 kDa) and is essential for substrate recognition of the N-terminus of gamma-secretase substrates derived from APP and Notch. Nicastrin facilitates substrate cleavage by the catalytic presenilin subunit in the gamma-secretase complex. One conserved glutamate is especially important, probably because this residue forms an ion pair with the amino terminus of the substrate. This substrate-binding domain is often called the DAP domain (named after DYIGS, the amino acid stretch that modulates amyloid precursor protein (APP) processing, and Peptidase homologous region). The sequence of the substrate N-terminus is apparently not critical for the interaction, but a free amino group is. Thus, nicastrin can be considered a kind of gatekeeper for the gamma-secretase complex: type I membrane proteins that have not shed their ectodomains cannot interact properly with nicastrin and do not gain access to the active site. Dysfunction of gamma-secretase is thought to cause Alzheimer's disease, with most mutations derived from Alzheimer's disease mapping to the catalytic subunit presenilin 1 (PS1).
Comment:The substrate-binding domain of nicastrin is often called the DAP domain (named after DYIGS, the amino acid stretch that modulates amyloid precursor protein (APP) processing, and Peptidase homologous region).
Jiyao W et al.(2023). "The conserved domain database in 2023.",