title: Quality control of glycoproteins bearing truncated glycans in an ALG9-defective (CDG-IL) patient.
abstract: We describe an ALG9-defective (congenital disorders of glycosylation type IL) patient who is homozygous for the p.Y286C (c.860A>G) mutation. This patient presented with psychomotor retardation, axial hypotonia, epilepsy, failure to thrive, inverted nipples, hepatomegaly, and pericardial effusion. Due to the ALG9 deficiency, the cells of this patient accumulated the lipid-linked oligosaccharides Man(6)GlcNAc(2)-PP-dolichol and Man(8)GlcNAc(2)-PP-dolichol. It is known that the oligosaccharide structure has a profound effect on protein glycosylation. Therefore, we investigated the influence of these truncated oligosaccharide structures on the protein transfer efficiency, the quality control of newly synthesized glycoproteins, and the eventual degradation of the truncated glycoproteins formed in this patient. We demonstrated that lipid-linked Man(6)GlcNAc(2) and Man(8)GlcNAc(2) are transferred onto proteins with the same efficiency. In addition, glycoproteins bearing these Man(6)GlcNAc(2) and Man(8)GlcNAc(2) structures efficiently entered in the glucosylation/deglucosylation cycle of the quality control system to assist in protein folding. We also showed that in comparison with control cells, patient's cells degraded misfolded glycoproteins at an increasing rate. The Man(8)GlcNAc(2) isomer C on the patient's glycoproteins was found to promote the degradation of misfolded glycoproteins.
authors.affiliation: Laboratory for Molecular Diagnosis, Center for Human Genetics, University of Leuven, Leuven, Belgium.
authors.forename: Wendy
authors.initials: W
authors.lastname: Vleugels
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Keldermans
authors.forename: Jaak
authors.initials: J
authors.lastname: Jaeken
authors.forename: Terry D
authors.initials: TD
authors.lastname: Butters
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Michalski
authors.forename: Gert
authors.initials: G
authors.lastname: Matthijs
authors.forename: François
authors.initials: F
authors.lastname: Foulquier
mesh_terms: D002239:Carbohydrate Metabolism, Inborn Errors / Q000235:genetics / Q000378:metabolism*; D004286:Dolichols / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007223:Infant; D008351:Mannans / Q000378:metabolism*; D008364:Mannosyltransferases / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D017510:Protein Folding
chemical_list: D004286:Dolichols; D006023:Glycoproteins; C404956:Man(6)GlcNAc(2)-PP-dolichol; C545279:Man(8)GlcNAc(2)-PP-dolichol; D008351:Mannans; D008565:Membrane Proteins; C469962:ALG9 protein, human; D008364:Mannosyltransferases