title: Defective ER associated degradation of a model luminal substrate in yeast carrying a mutation in the 4th ER luminal loop of Sec61p.
abstract: The major constituent of the eukaryotic ER protein-translocation channel (Sec61p in yeast, Sec61α in higher eukaryotes) shows a high degree of evolutionary conservation from yeast to humans. The vast majority of eukaryotic species have a conserved di-tyrosine in the 4th ER luminal loop. Previously, we discovered through a screen of ethylnitrosourea- (ENU-) mutagenized mice that substitution of the latter of these tyrosines with histidine (Y344H) of the murine Sec61α protein results in diabetes and hepatic steatosis in mice that is a result of ER stress. To further characterize the mechanism behind ER stress in these mice we made the homologous mutation in yeast Sec61p (Y345H). We found that this mutation increased sensitivity of yeast to ER stressing agents and to reduction of Inositol Requiring Enzyme 1 (IRE1) activity. Furthermore, we found that, while this mutation did not affect translocation, it did delay degradation of the model ER-associated degradation (ERAD) substrate CPY(∗). Replacing both ER luminal tyrosines with alanines resulted in a destabilization of the Sec61 protein that was rescued by over expression of Sss1p. This double mutant still lacked a noticeable translocation defect after stabilization by Sss1p, but exhibited a similar defect in CPY(∗) degradation.
authors.affiliation: The Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Wheeler
authors.forename: Nicholas
authors.initials: N
authors.lastname: Gekakis
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D060746:Endoplasmic Reticulum-Associated Degradation; D006602:Hexosyltransferases / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008956:Models, Chemical; D009154:Mutation; D014176:Protein Biosynthesis; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D006602:Hexosyltransferases; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase; C082863:IRE1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases