| Popis: |
Misfolded luminal endoplasmic reticulum (ER) proteins undergo ER-associated degradation (ERAD-L): they are retro-translocated into the cytosol, poly-ubiquitinated, and degraded by the proteasome. ERAD-L is mediated by the Hrd1 complex (composed of Hrd1, Hrd3, Der1, Usa1, and Yos9), but the mechanism of retro-translocation remains mysterious. Here, we report a structure of the active Hrd1 complex, as determined by cryo-EM analysis of two sub-complexes. Hrd3 and Yos9 jointly create a luminal binding site that recognizes glycosylated substrates. Hrd1 and the rhomboid-like Der1 protein form two “half-channels” with cytosolic and luminal cavities, respectively, and lateral gates facing one another in a thinned membrane region. Together with crosslinking and molecular dynamics simulation results, the structures suggest how a polypeptide loop of an ERAD-L substrate moves through the ER membrane. |
