A "Retrochaperone" Function for Cdc48: the Cdc48 Complex is Required for Retrotranslocated ERAD-M Substrate Solubility [Protein Synthesis and Degradation]

A surprising feature of ER-associated degradation (ERAD) is the movement, or retrotranslocation, of ubiquitinated substrates from the ER lumen or membrane to the cytosol where they are degraded by the 26S proteasome. Multispanning ER membrane proteins, called ERAD-M substrates, are retrotranslocated to the cytosol as full-length intermediates during ERAD and we have investigated how they maintain solubility. Using an in vivo assay, we show that retrotranslocated ERAD-M substrates are moved to the cytoplasm as part of the normal ERAD pathway, where they are part of a solely proteinacious complex. Using proteomics and direct biochemical confirmation, we found that Cdc48 serves as a critical retrochaperone for these ERAD-M substrates. Cdc48 binding to retrotranslocated, ubiquitinated ERAD-M substrates is required for their solubility; removal of the polyubiquitin chains, or competition for binding by addition of free polyubiquitin liberated Cdc48 from retrotranslocated proteins and rendered them insoluble. All components of the canonical Cdc48 complex Cdc48/Npl4/Ufd1 were present in solubilized ERAD-M substrates. This function of the complex was observed for both HRD and DOA pathway substrates. Thus, in addition to the long-known ATP-dependent extraction of ERAD substrates during retrotranslocation, the Cdc48 complex is generally and critically needed for the solubility of retrotranslocated ERAD-M intermediates.

from #AlexandrosSfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2iIVlAE
via IFTTT