title: Co-chaperone Specificity in Gating of the Polypeptide Conducting Channel in the Membrane of the Human Endoplasmic Reticulum.
abstract: In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic polypeptide-conducting channel, the heterotrimeric Sec61 complex. Previous work has characterized the Sec61 complex as a potential ER Ca(2+) leak channel in HeLa cells and identified ER lumenal molecular chaperone immunoglobulin heavy-chain-binding protein (BiP) as limiting Ca(2+) leakage via the open Sec61 channel by facilitating channel closing. This BiP activity involves binding of BiP to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344. Of note, the Y344H mutation destroys the BiP binding site and causes pancreatic β-cell apoptosis and diabetes in mice. Here, we systematically depleted HeLa cells of the BiP co-chaperones by siRNA-mediated gene silencing and used live cell Ca(2+) imaging to monitor the effects on ER Ca(2+) leakage. Depletion of either one of the ER lumenal BiP co-chaperones, ERj3 and ERj6, but not the ER membrane-resident co-chaperones (such as Sec63 protein, which assists BiP in Sec61 channel opening) led to increased Ca(2+) leakage via Sec6 complex, thereby phenocopying the effect of BiP depletion. Thus, BiP facilitates Sec61 channel closure (i.e. limits ER Ca(2+) leakage) via the Sec61 channel with the help of ERj3 and ERj6. Interestingly, deletion of ERj6 causes pancreatic β-cell failure and diabetes in mice and humans. We suggest that co-chaperone-controlled gating of the Sec61 channel by BiP is particularly important for cells, which are highly active in protein secretion, and that breakdown of this regulatory mechanism can cause apoptosis and disease.
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schorr
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Klein
authors.affiliation: Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany.
authors.forename: Igor
authors.initials: I
authors.lastname: Gamayun
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Armin
authors.initials: A
authors.lastname: Melnyk
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Martin
authors.initials: M
authors.lastname: Jung
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Nico
authors.initials: N
authors.lastname: Schäuble
authors.affiliation: the Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada, and.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: the Division of Biophysics, Universität Osnabrück, FB Biologie/Chemie, 49076 Osnabrück, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Hemmis
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Florian
authors.initials: F
authors.lastname: Bochen
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Markus
authors.initials: M
authors.lastname: Greiner
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Pavel
authors.initials: P
authors.lastname: Lampel
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Sabine Katharina
authors.initials: SK
authors.lastname: Urban
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Sarah
authors.initials: S
authors.lastname: Hassdenteufel
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and.
authors.forename: Johanna
authors.initials: J
authors.lastname: Dudek
authors.affiliation: the Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada, and.
authors.forename: Xing-Zhen
authors.initials: XZ
authors.lastname: Chen
authors.affiliation: the Division of Biophysics, Universität Osnabrück, FB Biologie/Chemie, 49076 Osnabrück, Germany.
authors.forename: Richard
authors.initials: R
authors.lastname: Wagner
authors.affiliation: Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany.
authors.forename: Adolfo
authors.initials: A
authors.lastname: Cavalié
authors.affiliation: From the Departments of Medical Biochemistry and Molecular Biology and richard.zimmermann@uks.eu.
authors.forename: Richard
authors.initials: R
authors.lastname: Zimmermann
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics; D003920:Diabetes Mellitus / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D020868:Gene Silencing; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D021381:Protein Transport; D000069816:SEC Translocation Channels
chemical_list: C494648:DNAJB11 protein, human; C494651:DNAJC3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D000069816:SEC Translocation Channels; C000613244:SEC61A1 protein, human; D002118:Calcium
keywords: BiP; ER calcium leakage; Sec61 complex gating; calcium imaging; cellular calcium homeostasis; chaperone; diabetes; endoplasmic reticulum (ER); protein translocation