title: ERAD and protein import defects in a sec61 mutant lacking ER-lumenal loop 7.
abstract: BACKGROUND
  The Sec61 channel mediates protein translocation across the endoplasmic reticulum (ER) membrane during secretory protein biogenesis, and likely also during export of misfolded proteins for ER-associated degradation (ERAD). The mechanisms of channel opening for the different modes of translocation are not understood so far, but the position of the large ER-lumenal loop 7 of Sec61p suggests a decisive role.
  
  
  RESULTS
  We show here that the Y345H mutation in L7 which causes diabetes in the mouse displays no ER import defects in yeast, but a delay in misfolded protein export. A complete deletion of L7 in Sec61p resulted in viable, cold- and tunicamycin-hypersensitive yeast cells with strong defects in posttranslational protein import of soluble proteins into the ER, and in ERAD of soluble substrates. Membrane protein ERAD was only moderately slower in sec61∆L7 than in wildtype cells. Although Sec61∆L7 channels were unstable in detergent, co-translational protein integration into the ER membrane, proteasome binding to Sec61∆L7 channels, and formation of hetero-heptameric Sec complexes were not affected.
  
  
  CONCLUSIONS
  We conclude that L7 of Sec61p is required for initiation of posttranslational soluble protein import into and misfolded soluble protein export from the ER, suggesting a key role for L7 in transverse gating of the Sec61 channel.
authors: Thomas
authors: T
authors: Tretter
authors: Fábio P
authors: FP
authors: Pereira
authors: Ozlem
authors: O
authors: Ulucan
authors: Volkhard
authors: V
authors: Helms
authors: Susanne
authors: S
authors: Allan
authors: Kai-Uwe
authors: KU
authors: Kalies
authors: Department of Microbiology, Faculty of Natural Sciences and Technology VIII, Saarland University, Campus A1,5, 66123 Saarbrücken, Germany. k.roemisch@mx.uni-saarland.de.
authors: Karin
authors: K
authors: Römisch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism; D060746:Endoplasmic Reticulum-Associated Degradation / Q000235:genetics*; D015870:Gene Expression; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein
chemical_list: D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins