title: A Golgi-localized mannosidase (MAN1B1) plays a non-enzymatic gatekeeper role in protein biosynthetic quality control.
abstract: Conformation-based disorders are manifested at the level of protein structure, necessitating an accurate understanding of how misfolded proteins are processed by the cellular proteostasis network. Asparagine-linked glycosylation plays important roles for protein quality control within the secretory pathway. The suspected role for the MAN1B1 gene product MAN1B1, also known as ER mannosidase I, is to function within the ER similar to the yeast ortholog Mns1p, which removes a terminal mannose unit to initiate a glycan-based ER-associated degradation (ERAD) signal. However, we recently discovered that MAN1B1 localizes to the Golgi complex in human cells and uncovered its participation in ERAD substrate retention, retrieval to the ER, and subsequent degradation from this organelle. The objective of the current study was to further characterize the contribution of MAN1B1 as part of a Golgi-based quality control network. Multiple lines of experimental evidence support a model in which neither the mannosidase activity nor catalytic domain is essential for the retention or degradation of the misfolded ERAD substrate Null Hong Kong. Instead, a highly conserved, vertebrate-specific non-enzymatic decapeptide sequence in the luminal stem domain plays a significant role in controlling the fate of overexpressed Null Hong Kong. Together, these findings define a new functional paradigm in which Golgi-localized MAN1B1 can play a mannosidase-independent gatekeeper role in the proteostasis network of higher eukaryotes.
authors.affiliation: Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030; Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Iannotti
authors.affiliation: Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030; Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Lauren
authors.initials: L
authors.lastname: Figard
authors.affiliation: Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030; Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Sokac
authors.affiliation: Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030; Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas 77030; Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030. Electronic address: rsifers@bcm.edu.
authors.forename: Richard N
authors.initials: RN
authors.lastname: Sifers
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D006056:Golgi Apparatus / Q000201:enzymology*; D006367:HeLa Cells; D006801:Humans; D008361:Mannosidases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D011786:Quality Control; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D008361:Mannosidases
keywords: Carbohydrate Glycoprotein; ER Quality Control; ER-associated Degradation; ERAD; Glycoprotein Secretion; Glycosidases; Protein Degradation; Protein Evolution; Protein Misfolding; Protein Sorting