title: The Peptidome of Behçet's Disease-Associated HLA-B*51:01 Includes Two Subpeptidomes Differentially Shaped by Endoplasmic Reticulum Aminopeptidase 1.
abstract: OBJECTIVE
  To characterize the peptidome of the Behçet's disease-associated HLA-B*51:01 allotype as well as the differential features of major peptide subsets and their distinct endoplasmic reticulum aminopeptidase 1 (ERAP-1)-mediated processing.
  
  
  METHODS
  The endogenous B*51:01-bound peptidome was characterized from 721.221 transfectant cells, after affinity chromatography and acid extraction, by tandem mass spectrometry. Recombinant ERAP-1 variants were used to digest synthetic B*51:01 ligands. HLA and transporter associated with antigen processing (TAP) binding affinities of peptide ligands were calculated with well-established algorithms. ERAP-1 and ERAP-2 from 721.221 cells were characterized by genomic sequencing and Western blotting.
  
  
  RESULTS
  The B*51:01 peptidome consisted of 29.5% octamers, 61.7% nonamers, 4.8% decamers, and 4.0% longer peptides. The major peptide motif consisted of Pro and Ala at position 2, aliphatic/aromatic position 3 residues, and Val and Ile at the C-terminal position. The ligands with Pro or Ala at position 2 constituted 2 distinct subpeptidomes. Peptides with Pro at position 2 showed higher affinity for B*51:01 and lower affinity for TAP than those with Ala at position 2. Most important, both peptide subsets differed drastically in the susceptibility of their position 1 residues to ERAP-1, revealing a distinct influence of this enzyme on both subpeptidomes, which may alter their balance, affecting the global affinity of B*51:01-peptide complexes.
  
  
  CONCLUSIONS
  ERAP-1 has a significant influence on the B*51:01 peptidome and its affinity. This influence is based on very distinct effects on the 2 subpeptidomes, whereby only peptides in the subpeptidome with Ala at position 2 are extensively destroyed, except when their position 1 residues are ERAP-1 resistant. This pattern provides a mechanism for the epistatic association of ERAP-1 and B*51:01 in Behçet's disease.
authors.affiliation: CSIC, Centro de Biología Molecular Severo Ochoa, Madrid, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Guasp
authors.affiliation: CSIC, Centro de Biología Molecular Severo Ochoa, Madrid, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Alvarez-Navarro
authors.affiliation: CSIC, Centro de Biología Molecular Severo Ochoa, Madrid, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Gomez-Molina
authors.affiliation: CSIC, Centro de Biología Molecular Severo Ochoa, Madrid, Spain.
authors.forename: Adrian
authors.initials: A
authors.lastname: Martín-Esteban
authors.affiliation: CSIC, Madrid, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Marcilla
authors.affiliation: Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Eilon
authors.initials: E
authors.lastname: Barnea
authors.affiliation: Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Arie
authors.initials: A
authors.lastname: Admon
authors.affiliation: CSIC, Centro de Biología Molecular Severo Ochoa, Madrid, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000626:Aminopeptidases / Q000235:genetics* / Q000378:metabolism; D001528:Behcet Syndrome / Q000378:metabolism*; D002460:Cell Line; D002846:Chromatography, Affinity; D005838:Genotype; D059949:HLA-B51 Antigen / Q000378:metabolism*; D006801:Humans; D015778:Minor Histocompatibility Antigens; D010455:Peptides / Q000378:metabolism*; D020641:Polymorphism, Single Nucleotide; D053719:Tandem Mass Spectrometry
chemical_list: D018528:ATP-Binding Cassette Transporters; D059949:HLA-B51 Antigen; D015778:Minor Histocompatibility Antigens; D010455:Peptides; C477327:transporter associated with antigen processing (TAP); D000626:Aminopeptidases; C464841:ERAP1 protein, human; C503944:ERAP2 protein, human