Hendershot: Identification and disposal of misfolded secretory pathway proteins

Proteins that fail to fold properly in the ER must be identified and retrotranslocated across the ER membrane for degradation by the 26S proteasome in a process that has been termed ER associated degradation (ERAD).  The turnover of unfolded glycoproteins that use the calnexin/calreticulin chaperone system has been the focus of a number of recent studies and involves recognition of modifications to the N-linked glycans that decorate these proteins.  However, much less is understood about how unglycosylated, misfolded proteins that rely on the BiP chaperone system for folding are distinguished from proteins that are in the process of folding.  We have recently begun to delineate this pathway and found that the disposal of BiP associated proteins requires they be partially unfolded.  Their transport back to the cytosol is dependent on Derin-1, Herp, the AAA ATPase p97, and Hrd1.  Derlin-1 and Herp do not appear to be required for the extraction of misfolded proteins that use the calnexin system, suggesting that there are distinct pathways for the disposal of these two groups of proteins.  To better understand this process, we are 1) examining the involvement of various ER DnaJ proteins in assisting BiP in folding versus degradation, 2) determining the structural features on proteins that allow them to be identified and retrotranslocated for degradation, and 3) investigating the role of various E3 ligases in the ubiquitination of ERAD substrates.