Self-association and BiP dissociation are not sufficient for activation of the ER stress sensor Ire1.
Ire1 is a type I transmembrane protein located on the endoplasmic reticulum (ER). Upon ER stress, Ire1 releases the ER chaperone BiP and self-associates. This activates Ire1 and triggers the unfolded protein response in the yeast Saccharomyces cerevisiae. We isolated and characterized an Ire1 luminal domain mutant lacking both the N-terminal and the juxtamembrane loosely folded subregions. Although this 'core' mutant was able to self-associate and failed to bind BiP even under nonstressed conditions, its activation was still dependent on ER stress. Furthermore, although substitution of Pro for Ser103 (S103P) in the luminal domain of full-length Ire1 caused neither BiP dissociation nor a change in self-association, the substitution in combination with the core mutation resulted in constitutive activation. This phenotype of the S103P mutation required a cluster of positively charged amino acid residues (Arg or Lys) located close to the mutation site in the Ire1 sequence. These observations indicate that in addition to BiP dissociation and self-association of Ire1, another unknown change on the luminal side is crucial for Ire1 activation.
Oikawa
Daisuke
D
Laboratory of Molecular and Cell Genetics, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
Kimata
Yukio
Y
Kohno
Kenji
K
D019943:Amino Acid Substitution; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D001665:Binding Sites; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D047468:Immunoprecipitation; D007763:Lac Operon / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology
D050976:Basic-Leucine Zipper Transcription Factors; C091341:HAC1 protein, S cerevisiae; D018840:HSP70 Heat-Shock Proteins; D008562:Membrane Glycoproteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014415:Tunicamycin; C082863:IRE1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases