title: Increased efficiency of folding and peptide loading of mutant MHC class I molecules.
abstract: Class I molecules, encoded by diverse alleles at several loci of the major histocompatibility complex (MHC) are assembled in the endoplasmic reticulum (ER) from heavy chain, beta2 microglobulin and peptide in association with accessory proteins of the peptide loading complex. We show here, that mutations in the alpha2 domain (Q115A; D122A) of the human class I allele HLA-A2 cause a lack of apparent association with the loading complex and a faster assembly. Despite the drastically reduced association with the TAP loading complex, i. e. less than 20 % of HLA-A2 expressed in the cells can be co-precipitated with either TAP, calreticulin or tapasin, the mutant proteins are expressed on the cell surface in a stable conformation, and bind a complex set of peptides almost identical to that of wild-type HLA-A2. Furthermore, the mutant class I molecules are more rapidly exported from the ER than wild-type HLA-A2 and undergo faster maturation. The mutation Q115A does not destroy a binding site for the loading complex as this HLA-A2 mutant associates with the loading complex when peptide supply is limited. The association of class I molecules with the TAP-associated loading complex appears to be a reflection of how quickly the stable conformation is gained.
authors.affiliation: Abteilung für Zellgenetik, Institut für Genetik, Universität zu Köln, Köln, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Beissbarth
authors.forename: J
authors.initials: J
authors.lastname: Sun
authors.forename: P B
authors.initials: PB
authors.lastname: Kavathas
authors.forename: B
authors.initials: B
authors.lastname: Ortmann
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000483:Alleles; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D017951:Antigen Presentation; D017920:Antiporters / Q000378:metabolism; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism; D037282:Calreticulin; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015789:HLA-A2 Antigen / Q000737:chemistry* / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D007700:Kinetics; D026901:Membrane Transport Proteins; D008958:Models, Molecular; D009154:Mutation; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D011233:Precipitin Tests; D011487:Protein Conformation; D017510:Protein Folding; D012261:Ribonucleoproteins / Q000378:metabolism; D014162:Transfection; D001613:beta 2-Microglobulin / Q000378:metabolism
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D015789:HLA-A2 Antigen; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; D010455:Peptides; D012261:Ribonucleoproteins; C073119:TAP1 protein, human; D001613:beta 2-Microglobulin; C107762:tapasin