title: Processing by endoplasmic reticulum mannosidases partitions a secretion-impaired glycoprotein into distinct disposal pathways.
abstract: In the early secretory pathway, a distinct set of processing enzymes and family of lectins facilitate the folding and quality control of newly synthesized glycoproteins. In this regard, we recently identified a mechanism in which processing by endoplasmic reticulum mannosidase I, which attenuates the removal of glucose from asparagine-linked oligosaccharides, sorts terminally misfolded alpha(1)-antitrypsin for proteasome-mediated degradation in response to its abrogated physical dissociation from calnexin (Liu, Y., Choudhury, P., Cabral, C., and Sifers, R. N. (1999) J. Biol. Chem. 274, 5861-5867). In the present study, we examined the quality control of genetic variant PI Z, which undergoes inappropriate polymerization following biosynthesis. Here we show that in stably transfected hepatoma cells the additional processing of asparagine-linked oligosaccharides by endoplasmic reticulum mannosidase II partitions variant PI Z away from the conventional disposal mechanism in response to an arrested posttranslational interaction with calnexin. Intracellular disposal is accomplished by a nonproteasomal system that functions independently of cytosolic components but is sensitive to tyrosine phosphatase inhibition. The functional role of ER mannosidase II in glycoprotein quality control is discussed.
authors.affiliation: Cell and Molecular Biology Graduate Program, Departments of Pathology and Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Cabral
authors.forename: P
authors.initials: P
authors.lastname: Choudhury
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: R N
authors.initials: RN
authors.lastname: Sifers
mesh_terms: D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002240:Carbohydrate Sequence; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D014644:Genetic Variation; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008114:Liver Neoplasms, Experimental; D008361:Mannosidases / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000378:metabolism; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012969:Sodium Fluoride / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014638:Vanadates / Q000494:pharmacology; D000515:alpha 1-Antitrypsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001152:Arsenicals; D006023:Glycoproteins; D009844:Oligosaccharides; D011994:Recombinant Proteins; D000515:alpha 1-Antitrypsin; C076715:pervanadate; C029341:oxophenylarsine; D019319:Okadaic Acid; D014638:Vanadates; D012969:Sodium Fluoride; D008361:Mannosidases; C046090:mannosyl-oligosaccharide 1,2-alpha-mannosidase