title: Analysis of the mutant HLA-A*0201 heavy chain H74L: impaired TAP-dependent peptide loading.
abstract: A mutation of the HLA-A*0201 heavy chain at position 74 from histidine to leucine (H74L) resulted in a molecule with an interesting phenotype. H74L-expressing targets were recognized by peptide-specific HLA-A*0201-restricted cytotoxic T lymphocytes at lower peptide concentrations than wild type HLA-A*0201. H74L's improved ability to sensitize cells for tysis was due to its enhanced capability to bind exogenous peptide. Furthermore, this phenotype of improved exogenous binding and functional recognition was not peptide-specific. In contrast, the H74L molecule failed to present the HIV- HLA-A2-restricted pol peptide when expressed and processed endogenously. The inability to bind endogenous pol could be rescued by preceding the pol peptide with a signal sequence. The defect affecting endogenous presentation, therefore, appeared to be limited to the TAP-dependent pathway. Surprisingly, the H74L heavy chain was able to enter the defined MHC class I pathway and associate with beta2M, calreticulin, tapasin, and TAP. Despite the presence of the H74L heavy chain at the TAP complex, H74L was functionally inefficient at loading TAP-dependent peptides. H74L may help elucidate further steps in the process of loading TAP-dependent peptides into the class I cleft.
authors.affiliation: Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, 27599-7290, USA.
authors.forename: R R
authors.initials: RR
authors.lastname: Caley
authors.forename: A L
authors.initials: AL
authors.lastname: Peace-Brewer
authors.forename: M
authors.initials: M
authors.lastname: Matsui
authors.forename: J A
authors.initials: JA
authors.lastname: Frelinger
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000276:immunology; D017951:Antigen Presentation; D001692:Biological Transport; D015684:Gene Products, pol / Q000276:immunology; D015497:HIV-1 / Q000276:immunology; D015789:HLA-A2 Antigen / Q000235:genetics / Q000276:immunology*; D015395:Histocompatibility Antigens Class I / Q000276:immunology; D006801:Humans; D007424:Intracellular Fluid / Q000276:immunology; D009154:Mutation; D010455:Peptides / Q000276:immunology; D011506:Proteins / Q000276:immunology; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000276:immunology
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015684:Gene Products, pol; D015789:HLA-A2 Antigen; D015395:Histocompatibility Antigens Class I; C031540:M-protein, influenza virus; D010455:Peptides; D011506:Proteins; C073119:TAP1 protein, human; D014763:Viral Matrix Proteins; C071692:TAP2 protein, human