title: Misfolded membrane proteins are specifically recognized by the transmembrane domain of the Hrd1p ubiquitin ligase.
abstract: Quality control pathways such as ER-associated degradation (ERAD) employ a small number of factors to specifically recognize a wide variety of protein substrates. Delineating the mechanisms of substrate selection is a principle goal in studying quality control. The Hrd1p ubiquitin ligase mediates ERAD of numerous misfolded proteins including soluble, lumenal ERAD-L and membrane-anchored ERAD-M substrates. We tested if the Hrd1p multispanning membrane domain was involved in ERAD-M specificity. In this work, we have identified site-directed membrane domain mutants of Hrd1p impaired only for ERAD-M and normal for ERAD-L. Furthermore, other Hrd1p variants were specifically deficient for degradation of individual ERAD-M substrates. Thus, the Hrd1p transmembrane region bears determinants of high specificity in the ERAD-M pathway. From in vitro and interaction studies, we suggest a model in which the Hrd1p membrane domain employs intramembrane residues to evaluate substrate misfolding, leading to selective ubiquitination of appropriate ERAD-M clients.
authors.affiliation: Section of Cell and Developmental Biology, Division of Biological Sciences, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
authors.forename: Brian K
authors.initials: BK
authors.lastname: Sato
authors.forename: Daniel
authors.initials: D
authors.lastname: Schulz
authors.forename: Phong H
authors.initials: PH
authors.lastname: Do
authors.forename: Randolph Y
authors.initials: RY
authors.lastname: Hampton
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D004721:Endoplasmic Reticulum / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D010641:Phenotype; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D013379:Substrate Specificity / Q000502:physiology; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D054875:Ubiquitination
chemical_list: D018528:ATP-Binding Cassette Transporters; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C092438:PDR5 protein, S cerevisiae; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C104621:HRD1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases