Calnexin discriminates between protein conformational states and functions as a molecular chaperone in vitro.
Although calnexin is thought to function as a molecular chaperone for glycoproteins, a prevalent view is that it cannot distinguish between protein conformational states, binding solely through its lectin site to monoglucosylated oligosaccharides. Using purified components in vitro, calnexin effectively prevented the aggregation not only of glycoproteins bearing monoglucosylated oligosaccharides but also proteins lacking N-glycans, an effect enhanced by ATP. It also suppressed the thermal denaturation of nonglycosylated proteins and enhanced their refolding in conjunction with other cellular components. Calnexin formed stable complexes with unfolded conformers of these proteins but not with the native molecules. Therefore, in addition to being a lectin, calnexin functions as a bona fide molecular chaperone capable of interacting with polypeptide segments of folding glycoproteins.
Ihara
Y
Y
Department of Biochemistry, University of Toronto, Ontario, Canada.
Cohen-Doyle
M F
MF
Saito
Y
Y
Williams
D B
DB
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002135:Calcium-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D037281:Calnexin; D002950:Citrate (si)-Synthase / Q000737:chemistry / Q000378:metabolism; D004285:Dogs; D005947:Glucose; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D006031:Glycosylation; D006358:Hot Temperature; D037102:Lectins / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000187:drug effects / Q000378:metabolism*; D009844:Oligosaccharides / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism; D037121:Plant Lectins; D011485:Protein Binding; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D017510:Protein Folding; D030262:Soybean Proteins; D010835:Phytohemagglutinins
D000255:Adenosine Triphosphate; D002135:Calcium-Binding Proteins; D037281:Calnexin; D002950:Citrate (si)-Synthase; D005947:Glucose; D006023:Glycoproteins; D037102:Lectins; D018832:Molecular Chaperones; D009844:Oligosaccharides; D010446:Peptide Fragments; D037121:Plant Lectins; D030262:Soybean Proteins; C028824:soybean lectin; D010835:Phytohemagglutinins