title: Der1 promotes movement of misfolded proteins through the endoplasmic reticulum membrane.
abstract: Misfolded proteins of the secretory pathway are extracted from the endoplasmic reticulum (ER), polyubiquitylated by a protein complex termed the Hmg-CoA reductase degradation ligase (HRD ligase) and degraded by cytosolic 26S proteasomes. The movement of these proteins through the lipid bilayer is assumed to occur via a protein-conducting channel of unknown nature. We show that the integral membrane protein Der1 oligomerizes, which relies on its interaction with the scaffolding protein Usa1. Mutations in the transmembrane domains of Der1 block the passage of soluble proteins across the ER membrane. As determined by site-specific photocrosslinking, the ER-luminal exposed parts of Der1 are in spatial proximity to the substrate receptor Hrd3, whereas the membrane-embedded domains reside adjacent to the ubiquitin ligase Hrd1. Intriguingly, both regions also form crosslinks to client proteins. Our data imply that Der1 initiates the export of aberrant polypeptides from the ER lumen by threading such molecules into the ER membrane and routing them to Hrd1 for ubiquitylation.
authors.affiliation: Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Mehnert
authors.affiliation: 1] Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany [2] Humboldt-University Berlin, Institute of Biology, Invalidenstraße 43, 10115 Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sommer
authors.affiliation: Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Straße 10, 13125 Berlin-Buch, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Jarosch
mesh_terms: D001577:Benzophenones / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics; D003432:Cross-Linking Reagents / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation; D007425:Intracellular Membranes / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000378:metabolism; D017510:Protein Folding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: C488060:4-benzoylphenylalanine; D001577:Benzophenones; D003432:Cross-Linking Reagents; C098515:DER1 protein, S cerevisiae; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D010649:Phenylalanine