title: N-linked glycosylation is required for nicotinic receptor assembly but not for subunit associations with calnexin.
abstract: We investigated how asparagine (N)-linked glycosylation affects assembly of acetylcholine receptors (AChRs) in the endoplasmic reticulum (ER). Block of N-linked glycosylation inhibited AChR assembly whereas block of glucose trimming partially blocked assembly at the late stages. Removal of each of seven glycans had a distinct effect on AChR assembly, ranging from no effect to total loss of assembly. Because the chaperone calnexin (CN) associates with N-linked glycans, we examined CN interactions with AChR subunits. CN rapidly associates with 50% or more of newly synthesized AChR subunits, but not with subunits after maturation. Block of N-linked glycosylation or trimming did not alter CN-AChR subunit associations nor did subunit mutations prevent N-linked glycosylation. Additionally, CN associations with subunits lacking N-linked glycans occurred without subunit aggregation or misfolding. Our data indicate that CN associates with AChR subunits without N-linked glycan interactions. Furthermore, CN-subunit associations only occur early in AChR assembly and have no role in events later that require N-linked glycosylation.
authors.affiliation: Committee on Neurobiology and Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Christian P
authors.initials: CP
authors.lastname: Wanamaker
authors.forename: William N
authors.initials: WN
authors.lastname: Green
mesh_terms: D001216:Asparagine / Q000378:metabolism; D037281:Calnexin / Q000502:physiology*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D007668:Kidney / Q000166:cytology; D011134:Polysaccharides / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D011978:Receptors, Nicotinic / Q000096:biosynthesis* / Q000737:chemistry*
chemical_list: D011134:Polysaccharides; D011978:Receptors, Nicotinic; D037281:Calnexin; D001216:Asparagine; D005947:Glucose