title: Combined effects of ankylosing spondylitis-associated ERAP1 polymorphisms outside the catalytic and peptide-binding sites on the processing of natural HLA-B27 ligands.
abstract: ERAP1 polymorphism involving residues 528 and 575/725 is associated with ankylosing spondylitis among HLA-B27-positive individuals. We used four recombinant variants to address the combined effects of the K528R and D575N polymorphism on the processing of HLA-B27 ligands. The hydrolysis of a fluorogenic substrate, Arg-528/Asp-575 < Lys-528/Asp-575 < Arg-528/Asn-575 < Lys-528/Asn-575, indicated that the relative activity of variants carrying Arg-528 or Lys-528 depends on residue 575. Asp-575 conferred lower activity than Asn-575, but the difference depended on residue 528. The same hierarchy was observed with synthetic precursors of HLA-B27 ligands, but the effects were peptide-dependent. Sometimes the epitope yields were variant-specific at all times. For other peptides, concomitant generation and destruction led to similar epitope amounts with all the variants at long, but not at short, digestion times. The generation/destruction balance of two related HLA-B27 ligands was analyzed in vitro and in live cells. Their relative yields at long digestion times were comparable with those from HLA-B27-positive cells, suggesting that ERAP1 was a major determinant of the abundance of these peptides in vivo. The hydrolysis of fluorogenic and peptide substrates by an HLA-B27 ligand or a shorter peptide, respectively, was increasingly inhibited as a function of ERAP1 activity, indicating that residues 528 and 575 affect substrate inhibition of ERAP1 trimming. The significant and complex effects of co-occurring ERAP1 polymorphisms on multiple HLA-B27 ligands, and their potential to alter the immunological and pathogenetic features of HLA-B27 as a function of the ERAP1 context, explain the epistatic association of both molecules in ankylosing spondylitis.
authors.affiliation: From the Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma), 28049 Madrid, Spain.
authors.forename: Adrian
authors.initials: A
authors.lastname: Martín-Esteban
authors.forename: Patricia
authors.initials: P
authors.lastname: Gómez-Molina
authors.forename: Alejandro
authors.initials: A
authors.lastname: Sanz-Bravo
authors.forename: José A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D000626:Aminopeptidases / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D015796:HLA-B27 Antigen / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D006801:Humans; D008024:Ligands; D015778:Minor Histocompatibility Antigens; D011110:Polymorphism, Genetic; D013167:Spondylitis, Ankylosing / Q000235:genetics / Q000276:immunology / Q000473:pathology
chemical_list: D000939:Epitopes; D015796:HLA-B27 Antigen; D008024:Ligands; D015778:Minor Histocompatibility Antigens; D000626:Aminopeptidases; C464841:ERAP1 protein, human
keywords: Aminopeptidase; Antigen Processing; Arthritis; Major Histocompatibility Complex (MHC); Pathogenesis; Peptides