A single bottleneck in HLA-C assembly.
Poor assembly of class I major histocompatibility HLA-C heavy chains results in their intracellular accumulation in two forms: free of and associated with their light chain subunit (beta(2)-microglobulin). Both intermediates are retained in the endoplasmic reticulum by promiscuous and HLA-dedicated chaperones and are poorly associated with peptide antigens. In this study, the eight serologically defined HLA-C alleles and the interlocus recombinant HLA-B46 allele (sharing the HLA-C-specific motif KYRV at residues 66-76 of the alpha1-domain alpha-helix) were compared with a large series of HLA-B and HLA-A alleles. Pulse-labeling experiments with HLA-C transfectants and HLA homozygous cell lines demonstrated that KYRV alleles accumulate as free heavy chains because of both poor assembly and post-assembly instability. Reactivity with antibodies to mapped linear epitopes, co-immunoprecipitation experiments, and molecular dynamics simulation studies additionally showed that the KYRV motif confers association to the HLA-dedicated chaperones TAP and tapasin as well as reduced plasticity and unfolding in the peptide-binding groove. Finally, in vitro assembly experiments in cell extracts of the T2 and 721.220 mutant cell lines demonstrated that HLA-Cw1 retains the ability to form a peptide-receptive interface despite a lack of TAP and functional tapasin, respectively. In the context of the available literature, these results indicate that a single locus-specific biosynthetic bottleneck renders HLA-C peptide-selective (rather than peptide-unreceptive) and a preferential natural killer cell ligand.
Sibilio
Leonardo
L
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy.
Martayan
Aline
A
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy.
Setini
Andrea
A
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy.
Monaco
Elisa Lo
EL
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy.
Tremante
Elisa
E
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy.
Butler
Richard H
RH
Cell Biology Institute, Consiglio Nazionale delle Ricerche, Via E. Ramarini 32, 00016 Monterotondo Scalo Rome, Italy.
Giacomini
Patrizio
P
Laboratory of Immunology, Regina Elena National Cancer Research Institute, Centro della Ricerca Sperimentale, Via delle Messi d'Oro 156, 00158 Rome, Italy. Electronic address: giacomini@ifo.it.
D000483:Alleles; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000276:immunology; D002460:Cell Line; D003198:Computer Simulation; D003720:Densitometry; D015235:HLA-B Antigens; D015236:HLA-C Antigens / Q000737:chemistry*; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018583:Pliability; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013816:Thermodynamics; D001613:beta 2-Microglobulin / Q000378:metabolism
D015235:HLA-B Antigens; D015236:HLA-C Antigens; C047431:HLA-Cw1 antigen; D026901:Membrane Transport Proteins; D001613:beta 2-Microglobulin; C107762:tapasin