4.G.1.1.1
Presenilin 1 of the γ-secretase (GS) complex.  Substrate proteins are recognized by their transmembrane domains, and nicastrin actively excludes larger substrates through steric hindrance, thus serving as a molecular gatekeeper for substrate binding and catalysis (Bolduc et al. 2015). γ-secretase interacts with the myoinositol transporter (TC#2.A.1.1.25), and this interaction regulates the activity of γ-secretase in its production of Abeta (Teranishi et al. 2015). See family description for more details. gamma-Secretase promotes membrane insertion of the human papillomavirus L2 capsid protein during viral infection (Inoue et al. 2018).
   Anterior pharynx-defective 1A (APH-1A) is a seven transmembrane component of gamma-secretase (GS), an aspartyl protease enzyme involved in the production of toxic amyloid-beta peptides in Alzheimer's disease patients. Cryo-EM structures of the enzyme complex revealed a central cavity in its APH-1A component, similar to water-containing cavities in G-protein coupled receptors (GPCRs). Aguayo-Ortiz and Dominguez 2019 performed molecular dynamics and umbrella sampling simulations to understand the role of the APH-1A cavity in the GS complex. APH-1A is able to store water molecules in its inner cavity and transport some of them between cell spaces. This allows the influx of extracellular cations into a central hydrophilic cavity but cannot transport them into the intracellular space. This may be an alternative APH-1A function besides its complex stabilization role (Aguayo-Ortiz and Dominguez 2019).