title: A novel UGGT1 and p97-dependent checkpoint for native ectodomains with ionizable intramembrane residue.
abstract: Only native polypeptides are released from the endoplasmic reticulum (ER) to be transported at the site of activity. Persistently misfolded proteins are retained and eventually selected for ER-associated degradation (ERAD). The paradox of a structure-based protein quality control is that functional polypeptides may be destroyed if they are architecturally unfit. This has health-threatening implications, as shown by the numerous "loss-of-function" proteopathies, but also offers chances to intervene pharmacologically to promote bypassing of the quality control inspection and export of the mutant, yet functional protein. Here we challenged the ER of human cells with four modular glycopolypeptides designed to alert luminal and membrane protein quality checkpoints. Our analysis reveals the unexpected collaboration of the cytosolic AAA-ATPase p97 and the luminal quality control factor UDP-glucose:glycoprotein glucosyltransferase (UGGT1) in a novel, BiP- and CNX-independent checkpoint. This prevents Golgi transport of a chimera with a native ectodomain that passes the luminal quality control scrutiny but displays an intramembrane defect. Given that human proteopathies may result from impaired transport of functional polypeptides with minor structural defects, identification of quality checkpoints and treatments to bypass them as shown here upon silencing or pharmacologic inhibition of UGGT1 or p97 may have important clinical implications.
authors.affiliation: Institute for Research in Biomedicine, Protein Folding and Quality Control, CH-6500 Bellinzona, Switzerland Università della Svizzera Italiana, CH-6900 Lugano, Switzerland Graduate School for Cellular and Biomedical Sciences, University of Bern, CH-3000 Bern, Switzerland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Merulla
authors.affiliation: Institute for Research in Biomedicine, Protein Folding and Quality Control, CH-6500 Bellinzona, Switzerland Università della Svizzera Italiana, CH-6900 Lugano, Switzerland.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Soldà
authors.affiliation: Institute for Research in Biomedicine, Protein Folding and Quality Control, CH-6500 Bellinzona, Switzerland Università della Svizzera Italiana, CH-6900 Lugano, Switzerland Ecole Polytechnique Fédérale de Lausanne, School of Life Sciences, CH-1015 Lausanne, Switzerland maurizio.molinari@irb.usi.ch.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Molinari
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D037281:Calnexin / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D060746:Endoplasmic Reticulum-Associated Degradation / Q000502:physiology*; D005964:Glucosyltransferases / Q000378:metabolism*; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D000099237:UDP-Galactose Translocators
chemical_list: D000251:Adenosine Triphosphatases; D037281:Calnexin; D000091342:Endoplasmic Reticulum Chaperone BiP; D005964:Glucosyltransferases; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D009687:Nuclear Proteins; C404942:p97 ATPase; C000731541:UGGT1 protein, human; D000099237:UDP-Galactose Translocators