The Luminal domain, a dimerization domain, of the Serine/Threonine protein kinase, Inositol-requiring protein 1
The Luminal domain is a dimerization domain present in Inositol-requiring protein 1 (IRE1), a serine/threonine protein kinase (STK) and a type I transmembrane protein that is localized in the endoplasmic reticulum (ER). IRE1, also called Endoplasmic reticulum (ER)-to-nucleus signaling protein (or ERN), is a kinase receptor that also contains an endoribonuclease domain in the cytoplasmic side. It plays 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 acts as an ER stress sensor and is the oldest and most conserved component of the UPR in eukaryotes. During ER stress, IRE1 dimerizes through its luminal domain and forms oligomers, allowing the kinase domain to undergo trans-autophosphorylation. This leads to a conformational change that stimulates its endoribonuclease activity and 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. Mammals contain two IRE1 proteins, IRE1alpha (or ERN1) and IRE1beta (or ERN2). IRE1alpha is expressed in all cells and tissues while IRE1beta is found only in intestinal epithelial cells.
Jiyao W et al.(2023). "The conserved domain database in 2023.",