What is ERAD?
ERAD is ER-associated degradation, the pathway that recognizes misfolded ER proteins, retrotranslocates them, ubiquitinates them, and degrades them via the proteasome
How are proteins targeted for ERAD through mannosidases?
Mannose trimming acts as a time-dependent quality-control signal: if a protein fails to fold in time, mannosidase-mediated trimming marks it for ERAD recognition
Describe protein glycosylation in the ER.
Proteins entering the ER receive N-linked glycans, which are then trimmed and used in the calnexin/calreticulin folding cycle to monitor folding status
Which major factors/enzymes participate in ER glycosylation?
Major factors include OST, glucosidase I, glucosidase II, UGGT, calreticulin/calnexin, PDI, and Ero1.
Describe the protein-folding cycle in the ER. (Drawing also allowed)
Nascent proteins enter through the translocon, are glycosylated by OST, trimmed by glucosidases, bind CNX/CRT, undergo disulfide-bond formation via PDI/Ero1, and if not properly folded are reglucosylated by UGGT for another cycle or sent to ERAD if folding fails.
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