Recognition of an ERAD-L substrate analyzed by site-specific in vivo photocrosslinking.

Misfolded, luminal endoplasmic reticulum (ER) proteins must be recognized before being degraded by a process called ERAD-L. Using site-specific photocrosslinking in Saccharomyces cerevisiae, we tested luminal interactions of a glycosylated ERAD-L substrate with potential recognition components. Major interactions were observed with Hrd3p. These are independent of the glycan and of other ERAD components, and can occur throughout the length of the unfolded substrate. The lectin Yos9p only interacts with a polypeptide segment distant from the degradation signal. Hrd3p may thus be the first substrate-recognizing component. Der1p appears to have a role in a pathway that is parallel to that involving Hrd3p.