title: A role for calnexin in the assembly of the MHC class I loading complex in the endoplasmic reticulum.
abstract: Heterodimers of MHC class I glycoprotein and beta(2)-microglobulin (beta(2)m) bind short peptides in the endoplasmic reticulum (ER). Before peptide binding these molecules form part of a multisubunit loading complex that also contains the two subunits of the TAP, the transmembrane glycoprotein tapasin, the soluble chaperone calreticulin, and the thiol oxidoreductase ERp57. We have investigated the assembly of the loading complex and provide evidence that after TAP and tapasin associate with each other, the transmembrane chaperone calnexin and ERp57 bind to the TAP-tapasin complex to generate an intermediate. These interactions are independent of the N:-linked glycan of tapasin, but require its transmembrane and/or cytoplasmic domain. This intermediate complex binds MHC class I-beta(2)m dimers, an event accompanied by the loss of calnexin and the acquisition of calreticulin, generating the MHC class I loading complex. Peptide binding then induces the dissociation of MHC class I-beta(2)m dimers, which can be transported to the cell surface.
authors.affiliation: Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: G
authors.initials: G
authors.lastname: Diedrich
authors.forename: N
authors.initials: N
authors.lastname: Bangia
authors.forename: M
authors.initials: M
authors.lastname: Pan
authors.forename: P
authors.initials: P
authors.lastname: Cresswell
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism / Q000502:physiology; D017920:Antiporters / Q000378:metabolism / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D037281:Calnexin; D037282:Calreticulin; D002461:Cell Line, Transformed; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D006680:HLA Antigens / Q000378:metabolism*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism / Q000502:physiology; D007535:Isomerases / Q000378:metabolism; D007700:Kinetics; D008285:Major Histocompatibility Complex; D026901:Membrane Transport Proteins; D011485:Protein Binding / Q000276:immunology; D019704:Protein Disulfide-Isomerases; D012261:Ribonucleoproteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D006680:HLA Antigens; D006360:Heat-Shock Proteins; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; D012261:Ribonucleoproteins; C073119:TAP1 protein, human; C107762:tapasin; D037281:Calnexin; D007535:Isomerases; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human