Polyubiquitin serves as a recognition signal, rather than a ratcheting molecule, during retrotranslocation of proteins across the endoplasmic reticulum membrane

Dennis Flierman, Yihong Ye, Min Dai, Vincent Chau, Tom A. Rapoport

    Research output: Contribution to journalArticlepeer-review

    85 Scopus citations

    Abstract

    Polyubiquitination is required for retrotranslocation of proteins from the endoplasmic reticulum back into the cytosol, where they are degraded by the proteasome. We have tested whether the release of a polypeptide chain into the cytosol is caused by a ratcheting mechanism in which the attachment of polyubiquitin prevents the chain from moving back into the endoplasmic reticulum. Using a permeabilized cell system in which major histocompatibility complex class I heavy chains are retrotranslocated under the influence of the human cytomegalovirus protein US11, we demonstrate that polyubiquitination alone is insufficient to provide the driving force for retrotranslocation. Substrate release into the cytosol requires an additional ATP-dependent step. Release requires a lysine 48 linkage of ubiquitin chains. It does not occur when polyubiquitination of the substrate is carried out with glutathione S-transferase (GST)-ubiquitin, and this correlates with poly-GST-ubiquitin not being recognized by a ubiquitin-binding domain in the Ufdl-Npl4 cofactor of the ATPase p97. These data suggest that polyubiquitin does not serve as a ratcheting molecule. Rather, it may serve as a recognition signal for the p97-Ufdl-Np14 complex, a component implicated in the movement of substrate into the cytosol.

    Original languageEnglish (US)
    Pages (from-to)34774-34782
    Number of pages9
    JournalJournal of Biological Chemistry
    Volume278
    Issue number37
    DOIs
    StatePublished - Sep 12 2003

    All Science Journal Classification (ASJC) codes

    • Biochemistry
    • Molecular Biology
    • Cell Biology

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