title: Deficiency of α-glucosidase I alters glycoprotein glycosylation and lifespan in Caenorhabditis elegans.
abstract: Endoplasmic reticulum (ER) α-glucosidase I is an enzyme that trims the distal α1,2-linked glucose (Glc) residue from the Glc3Man9GlcNAc2 oligosaccharide following its addition to nascent glycoproteins in the initial step of processing. This reaction is critical to the subsequent processing of N-glycans and thus defects in α-glucosidase I gene in human cause congenital disorder of glycosylation (CDG) type IIb. We identified the Caenorhabditis elegans α-glucosidase I gene (F13H10.4, designated agl-1) that encodes a polypeptide with 36% identity to human α-glucosidase I. The agl-1 cDNA restored the expression of complex-type N-glycans on the cell surface of α-glucosidase I-defective Chinese hamster ovary Lec23 cells. RNAi knockdown of agl-1 [agl-1(RNAi)] produced worms that were visibly similar to wild-type, but lifespan was reduced to about half of the control. Analyses of N-glycosylation in agl-1(RNAi) animals by western blotting and mass spectrometry showed reduction of paucimannose and complex-type glycans and dramatic increase of glucosylated oligomannose glycans. In addition, a significant amount of unusual terminally fucosylated N-glycans were found in agl-1(RNAi) animals. ER stress response was also provoked, leading to the accumulation of large amounts of triglucosylated free oligosaccharides (FOSs) (Glc3Man4-5GlcNAc1-2) in agl-1(RNAi) animals. Acceleration of ER-associated degradation in response to the accumulation of unfolded glycoproteins and insufficient interaction with calnexin/calreticulin in the ER lumen likely accounts for the increase of FOSs. Taken together, these studies in C. elegans demonstrate that decreased ER α-glucosidase I affects the entire N-glycan profile and induces chronic ER stress, which may contribute to the pathophysiology of CDG-IIb in humans.
authors.affiliation: Complex Carbohydrate Research Center, The University of Georgia, Athens, GA 30602-4712, USA.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Katoh
authors.forename: Juri
authors.initials: J
authors.lastname: Takase
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Tani
authors.forename: Ryuta
authors.initials: R
authors.lastname: Amamoto
authors.forename: Naofumi
authors.initials: N
authors.lastname: Aoshima
authors.forename: Michael
authors.initials: M
authors.lastname: Tiemeyer
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Hisashi
authors.initials: H
authors.lastname: Ashida
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D059865:Endoplasmic Reticulum Stress; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D008136:Longevity; D009844:Oligosaccharides / Q000378:metabolism; D059748:Proteolysis; D034741:RNA, Small Interfering / Q000235:genetics; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D006023:Glycoproteins; D009844:Oligosaccharides; D034741:RNA, Small Interfering; C587193:AGL-1 protein, C elegans; D000520:alpha-Glucosidases
keywords: Caenorhabditis elegans; N-glycan; congenital disorder of glycosylation; free oligosaccharide; α-glucosidase I