title: EDEM3, a soluble EDEM homolog, enhances glycoprotein endoplasmic reticulum-associated degradation and mannose trimming.
abstract: Quality control in the endoplasmic reticulum ensures that only properly folded proteins are retained in the cell through mechanisms that recognize and discard misfolded or unassembled proteins in a process called endoplasmic reticulum-associated degradation (ERAD). We previously cloned EDEM (ER degradation-enhancing alpha-mannosidase-like protein) and showed that it accelerates ERAD of misfolded glycoproteins. We now cloned mouse EDEM3, a soluble homolog of EDEM. EDEM3 consists of 931 amino acids and has all the signature motifs of Class I alpha-mannosidases (glycosyl hydrolase family 47) in its N-terminal domain and a protease-associated motif in its C-terminal region. EDEM3 accelerates glycoprotein ERAD in transfected HEK293 cells, as shown by increased degradation of misfolded alpha1-antitrypsin variant (null (Hong Kong)) and of TCRalpha. Overexpression of EDEM3 also greatly stimulates mannose trimming not only from misfolded alpha1-AT null (Hong Kong) but also from total glycoproteins, in contrast to EDEM, which has no apparent alpha1,2-mannosidase activity. Furthermore, overexpression of the E147Q EDEM3 mutant, which has the mutation in one of the conserved acidic residues essential for enzyme activity of alpha1,2-mannosidases, abolishes the stimulation of mannose trimming and greatly decreases the stimulation of ERAD by EDEM3. These results show that EDEM3 has alpha1,2-mannosidase activity in vivo, suggesting that the mechanism whereby EDEM3 accelerates glycoprotein ERAD is different from that of EDEM.
authors.affiliation: Department of Molecular and Cellular Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8397, Japan, CREST, JST, Saitama 332-0012, Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Hirao
authors.forename: Yuko
authors.initials: Y
authors.lastname: Natsuka
authors.forename: Taku
authors.initials: T
authors.lastname: Tamura
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wada
authors.forename: Daisuke
authors.initials: D
authors.lastname: Morito
authors.forename: Shunji
authors.initials: S
authors.lastname: Natsuka
authors.forename: Pedro
authors.initials: P
authors.lastname: Romero
authors.forename: Barry
authors.initials: B
authors.lastname: Sleno
authors.forename: Linda O
authors.initials: LO
authors.lastname: Tremblay
authors.forename: Annette
authors.initials: A
authors.lastname: Herscovics
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nagata
authors.forename: Nobuko
authors.initials: N
authors.lastname: Hosokawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000502:physiology*; D020224:Expressed Sequence Tags; D006023:Glycoproteins / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D017510:Protein Folding; D012995:Solubility; D043323:alpha-Mannosidase / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; C510458:EDEM3 protein, mouse; D043323:alpha-Mannosidase; D008358:Mannose