title: Glycan-dependent and -independent association of vesicular stomatitis virus G protein with calnexin.
abstract: Calnexin (CNX) is a membrane-bound molecular chaperone that associates with newly synthesized proteins in the endoplasmic reticulum. Although several studies have indicated that it interacts exclusively with glycoproteins that carry monoglucosylated N-linked oligosaccharides, others have reported that it can bind to proteins that have no glycans. To address this discrepancy, we translated wild-type vesicular stomatitis virus G protein and nonglycosylated mutant forms in the presence of microsomes and examined their association with CNX. Individual G protein molecules were found to efficiently associate with CNX when both glycans were present and less efficiently if there was only a single glycan. Nonglycosylated G protein also interacted with CNX, but only when misfolded and present in high molecular weight aggregates. The results indicated that CNX can interact with G protein in two ways: through an oligosaccharide-dependent mechanism that involves individual substrate proteins; and in an oligosaccharide-independent association with large aggregates.
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Cannon
authors.forename: D N
authors.initials: DN
authors.lastname: Hebert
authors.forename: A
authors.initials: A
authors.lastname: Helenius
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D037281:Calnexin; D016384:Consensus Sequence; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D008562:Membrane Glycoproteins; D008861:Microsomes / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010957:Plasmids; D017354:Point Mutation; D014176:Protein Biosynthesis; D017510:Protein Folding; D011817:Rabbits; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D017384:Sequence Deletion; D014158:Transcription, Genetic; D014162:Transfection; D014721:Vesicular stomatitis Indiana virus / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; C028391:G protein, vesicular stomatitis virus; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D014759:Viral Envelope Proteins; D037281:Calnexin