title: Calreticulin functions in vitro as a molecular chaperone for both glycosylated and non-glycosylated proteins.
abstract: Calreticulin (CRT) is thought to be a molecular chaperone that interacts with glycoproteins exclusively through a lectin site specific for monoglucosylated oligosaccharides. However, this chaperone function has never been directly demonstrated nor is it clear how lectin-oligosaccharide interactions facilitate glycoprotein folding. Using purified components, we show that CRT suppresses the aggregation not only of a glycoprotein bearing monoglucosylated oligosaccharides but also that of non-glycosylated proteins. Furthermore, CRT forms stable complexes with unfolded, non-glycosylated substrates but does not associate with native proteins. ATP and Zn(2+) enhance CRT's ability to suppress aggregation of non- glycoproteins, whereas engagement of its lectin site with purified oligosaccharide attenuates this function. CRT also confers protection against thermal inactivation and maintains substrates in a folding-competent state. We conclude that in addition to being a lectin CRT possesses a polypeptide binding capacity capable of discriminating between protein conformational states and that it functions in vitro as a classical molecular chaperone.
authors.affiliation: Department of Biochemistry, Medical Sciences Building, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Y
authors.initials: Y
authors.lastname: Saito
authors.forename: Y
authors.initials: Y
authors.lastname: Ihara
authors.forename: M R
authors.initials: MR
authors.lastname: Leach
authors.forename: M F
authors.initials: MF
authors.lastname: Cohen-Doyle
authors.forename: D B
authors.initials: DB
authors.lastname: Williams
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000502:physiology*; D037282:Calreticulin; D002712:Chlorides / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000378:metabolism; D006031:Glycosylation; D007136:Immunoglobulins / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008854:Microscopy, Electron; D018832:Molecular Chaperones / Q000502:physiology*; D009844:Oligosaccharides / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D011817:Rabbits; D012261:Ribonucleoproteins / Q000502:physiology*; D012542:Scattering, Radiation; D013696:Temperature; D013997:Time Factors; D017967:Zinc Compounds / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002712:Chlorides; C016512:IgY; D007136:Immunoglobulins; D037102:Lectins; D018832:Molecular Chaperones; D009844:Oligosaccharides; D012261:Ribonucleoproteins; D017967:Zinc Compounds; C016837:zinc chloride; D000255:Adenosine Triphosphate; D008291:Malate Dehydrogenase; D002950:Citrate (si)-Synthase