The stress-sensing domain of activated IRE1α forms helical filaments in narrow ER membrane tubes

• DOI: 10.1101/2021.02.24.432779
• Publication Date: 2021-02-25T09:00:17Z
• Authors: Stephen D. Carter; Ngoc-Han Tran; Ann De Mazière; Avi Ashkenazi; Judith Klumperman; Grant J. Jensen; Peter Walter
• Keywords: 570; General Science & Technology; 610; Protein Serine-Threonine Kinases; Cell Line; 03 medical and health sciences; Research Support, N.I.H., Extramural; Protein Domains; Cell Line, Tumor; Endoribonucleases; Journal Article; Humans; General; 0303 health sciences; Tumor; Cryoelectron Microscopy; Biological Sciences; Endoplasmic Reticulum Stress; 620; Unfolded Protein Response; Biochemistry and Cell Biology; Generic health relevance; Protein Multimerization; Research Support, U.S. Gov't, Non-P.H.S.; Signal Transduction

The signaling network of the unfolded protein response (UPR) adjusts the protein folding capacity of the endoplasmic reticulum (ER) according to need. The most conserved UPR sensor, IRE1α, spans the ER membrane and activates through oligomerization. IRE1α oligomers accumulate in dynamic foci. We determined thein-situstructure of IRE1α foci by cryogenic correlated light and electron microscopy (cryo-CLEM), combined with electron cryo-tomography (cryo-ET) and complementary immuno-electron microscopy. IRE1α oligomers localize to a network of narrow anastomosing ER tubes (diameter ~28 nm) with complex branching. The lumen of the tubes contains protein filaments, likely composed of linear arrays of IRE1α lumenal domain dimers, arranged in two intertwined, left-handed helices. Our findings define a previously unrecognized ER subdomain and suggest positive feedback in IRE1 signaling.