title: Mammalian ER mannosidase I resides in quality control vesicles, where it encounters its glycoprotein substrates.
abstract: Endoplasmic reticulum α1,2 mannosidase I (ERManI), a central component of ER quality control and ER-associated degradation (ERAD), acts as a timer enzyme, modifying N-linked sugar chains of glycoproteins with time. This process halts glycoprotein folding attempts when necessary and targets terminally misfolded glycoproteins to ERAD. Despite the importance of ERManI in maintenance of glycoprotein quality control, fundamental questions regarding this enzyme remain controversial. One such question is the subcellular localization of ERManI, which has been suggested to localize to the ER membrane, the ER-derived quality control compartment (ERQC), and, surprisingly, recently to the Golgi apparatus. To try to clarify this controversy, we applied a series of approaches that indicate that ERManI is located, at the steady state, in quality control vesicles (QCVs) to which ERAD substrates are transported and in which they interact with the enzyme. Both endogenous and exogenously expressed ERManI migrate at an ER-like density on iodixanol gradients, suggesting that the QCVs are derived from the ER. The QCVs are highly mobile, displaying dynamics that are dependent on microtubules and COP-II but not on COP-I vesicle machinery. Under ER stress conditions, the QCVs converge in a juxtanuclear region, at the ERQC, as previously reported. Our results also suggest that ERManI is turned over by an active autophagic process. Of importance, we found that membrane disturbance, as is common in immunofluorescence methods, leads to an artificial appearance of ERManI in a Golgi pattern.
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Ron
authors.initials: R
authors.lastname: Benyair
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Navit
authors.initials: N
authors.lastname: Ogen-Shtern
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Niv
authors.initials: N
authors.lastname: Mazkereth
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Ben
authors.initials: B
authors.lastname: Shai
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ehrlich
authors.affiliation: Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel gerardo@post.tau.ac.il.
authors.forename: Gerardo Z
authors.initials: GZ
authors.lastname: Lederkremer
mesh_terms: D000818:Animals; D001343:Autophagy; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D059865:Endoplasmic Reticulum Stress; D060746:Endoplasmic Reticulum-Associated Degradation; D031541:Fluorescence Resonance Energy Transfer; D006023:Glycoproteins / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008361:Mannosidases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D041681:NIH 3T3 Cells; D013379:Substrate Specificity; D059008:Time-Lapse Imaging / Q000379:methods
chemical_list: D006023:Glycoproteins; D008164:Luminescent Proteins; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D008361:Mannosidases; C046090:mannosyl-oligosaccharide 1,2-alpha-mannosidase