Misfolded proteins in the ER lumen are recognized and transported back to the cytosol for degradation by the ER-associated degradation or ERAD pathway. The pathway starts in the ER lumen with the enzyme α-mannosidase I, interacting with the terminally misfolded protein to trim mannose residues from the attached glycans. OS-9, a lectin chaperone bound to the luminal domain of the protein retrotranslocation complex, recognizes the trimmed glycan on the misfolded protein. Hrd1 protein is the crucial member of this complex that acts as a channel as well as a ubiquitin ligase. Other constituent proteins of the retrotranslocation complex push the misfolded protein into the Hrd1 channel. As the protein emerges on the cytosolic side, it is ubiquitinated by the Hrd1 protein, while the N-glycanase removes the attached glycans. The ubiquitinated protein segment then recruits the newly assembled Cdc48 AAA-ATPase complex, which uses ATP hydrolysis to pull the remaining protein through the channel. After the complete retrotranslocation into the cytosol, chaperones like Bag6 pass on the ubiquitinated protein into the proteasome for degradation.