title: Presentation of cytosolically stable peptides by HLA-B27 is not dependent on the canonic interactions of N-terminal basic residues in the A pocket.
abstract: HLA-B27 binds peptides with R at position 2. Additionally, a substantial fraction of the HLA-B27-bound peptide repertoire has basic residues at position 1. It is unclear whether this is determined by structural complementarity with the A pocket of the peptide-binding site, by the increased availability of peptides with dibasic N-terminal sequences resulting from their cytosolic stability, or both. To distinguish between these possibilities two B*2705 mutants were generated in which one or two A pocket surface residues stabilizing the peptidic R1 side chain were changed: E163T and E163T-W167S. Both mutants bound a large fraction of the constitutive peptide repertoire of B*2705. Moreover, 90 B*2705 ligands of known sequence were examined for their endogenous presentation by the mutants. The E163T mutation alone had a limited effect on binding of peptides with R1 or K1 and on the relative frequencies of N-terminal residues. However, it decreased the overall stability of the molecule. The E163T-W167S mutant also bound many of the B*2705 ligands with N-terminal basic residues, but its preference for G1 was significantly decreased. The results indicate that the capacity of HLA-B27 to bind peptides with N-terminal basic residues is largely independent of the canonic interactions that stabilize at least the R1 side chain. Thus, the prevalence of HLA-B27 ligands with dibasic N-terminal sequences may be significantly influenced by the increased availability of these peptides resulting from their cytosolic stability. This confers to HLA-B27 a unique capacity to present Ags generated in low amounts, but resistant to intracellular degradation.
authors.affiliation: Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), Universidad Autónoma, Madrid, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Gómez
authors.forename: Carla
authors.initials: C
authors.lastname: Mavian
authors.forename: Begoña
authors.initials: B
authors.lastname: Galocha
authors.forename: Noel
authors.initials: N
authors.lastname: García-Medel
authors.forename: José A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology*; D045744:Cell Line, Tumor; D003600:Cytosol / Q000276:immunology* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology; D018698:Glutamic Acid / Q000235:genetics; D015235:HLA-B Antigens / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D015796:HLA-B27 Antigen; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000276:immunology / Q000378:metabolism; D008024:Ligands; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D012694:Serine / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013816:Thermodynamics; D013912:Threonine / Q000235:genetics; D014364:Tryptophan / Q000235:genetics
chemical_list: D015235:HLA-B Antigens; C464936:HLA-B*27:05 antigen; D015796:HLA-B27 Antigen; D008024:Ligands; D010446:Peptide Fragments; D013912:Threonine; D018698:Glutamic Acid; D012694:Serine; D014364:Tryptophan