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The Luminal domain, a dimerization domain, of Inositol-requiring protein 1-like proteins The Luminal domain is a dimerization domain present in Inositol-requiring protein 1 (IRE1), eukaryotic translation Initiation Factor 2-Alpha Kinase 3 (EIF2AK3), and similar proteins. IRE1 and EIF2AK3 are serine/threonine protein kinases (STKs) and are type I transmembrane proteins that are localized in the endoplasmic reticulum (ER). They are kinase receptors that are activated through the release of BiP, a chaperone bound to their luminal domains under unstressed conditions. This results in dimerization through their luminal domains, allowing trans-autophosphorylation of their kinase domains and activation. They play roles in the signaling of the unfolded protein response (UPR), which is activated when protein misfolding is detected in the ER in order to decrease the synthesis of new proteins and increase the capacity of the ER to cope with the stress. IRE1, also called Endoplasmic reticulum (ER)-to-nucleus signaling protein (or ERN), contains an endoribonuclease domain in its cytoplasmic side and acts as an ER stress sensor. It is the oldest and most conserved component of the UPR in eukaryotes. Its activation results in the cleavage of its mRNA substrate, HAC1 in yeast and Xbp1 in metazoans, promoting a splicing event that enables translation into a transcription factor which activates the UPR. EIF2AK3, also called PKR-like Endoplasmic Reticulum Kinase (PERK), phosphorylates the alpha subunit of eIF-2, resulting in the downregulation of protein synthesis. It functions as the central regulator of translational control during the UPR pathway. In addition to the eIF-2 alpha subunit, EIF2AK3 also phosphorylates Nrf2, a leucine zipper transcription factor which regulates cellular redox status and promotes cell survival during the UPR. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",