title: Polymorphisms in the F Pocket of HLA-B27 Subtypes Strongly Affect Assembly, Chaperone Interactions, and Heavy-Chain Misfolding.
abstract: HLA-B27 is associated with the inflammatory spondyloarthritides (SpA), although subtypes HLA-B*27:06 and HLA-B*27:09 are not. These subtypes differ from the HLA-B*27:05 disease-associated allele primarily at residues 114 and 116 of the heavy chain, part of the F pocket of the antigen-binding groove. Dimerization of HLA-B27 during assembly has been implicated in disease onset. The purpose of this study was to investigate the factors that influence differences in dimerization between disease-associated and non-disease-associated HLA-B27 alleles.
  
  
  
  HLA-B*27:05 and mutants resembling the HLA-B*27:06 and 09 subtypes were expressed in the rat C58 T cell line, the human CEM T cell line and its calnexin-deficient variant CEM.NKR. Immunoprecipitation, pulse-chase experiments, flow cytometry, and immunoblotting were performed to study the assembly kinetics, heavy-chain dimerization, and chaperone associations.
  
  
  
  By expressing HLA-B*27:05, 06-like, and 09 alleles on a restrictive rat transporter associated with antigen processing background, we demonstrate that a tyrosine expressed at p116, either alone or together with an aspartic acid residue at p114, inhibited HLA-B27 dimerization and increased the assembly rate. F-pocket residues altered the associations with chaperones of the early major histocompatibility complex class I folding pathway. Calnexin was demonstrated to participate in endoplasmic reticulum (ER) stress-mediated degradation of dimers, whereas the oxidoreductase ERp57 does not appear to influence dimerization.
  
  
  
  Residues within the F pocket of the peptide-binding groove, which differ between disease-associated and non-disease-associated HLA-B27 subtypes, can influence the assembly process and heavy-chain dimerization, events which have been linked to the initiation of disease pathogenesis.
authors.affiliation: Stratford Campus, University of East London, London, UK.
authors.forename: David B
authors.initials: DB
authors.lastname: Guiliano
authors.affiliation: NHS Blood and Transplant, Colindale Blood Centre, London, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: North
authors.affiliation: NHS North West Surrey Clinical Commissioning Group, Weybridge, UK.
authors.forename: Eleni
authors.initials: E
authors.lastname: Panayoitou
authors.affiliation: University of St. Andrews, St. Andrews, UK.
authors.forename: Elaine C
authors.initials: EC
authors.lastname: Campbell
authors.affiliation: University of Oxford, Oxford, UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: McHugh
authors.affiliation: University of St. Andrews, St. Andrews, UK.
authors.forename: Fiona G M
authors.initials: FG
authors.lastname: Cooke
authors.affiliation: University of St. Andrews, St. Andrews, UK.
authors.forename: Marine
authors.initials: M
authors.lastname: Silvestre
authors.affiliation: University of Oxford, Oxford, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Bowness
authors.affiliation: University of St. Andrews, St. Andrews, UK.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Powis
authors.affiliation: Stratford Campus, University of East London, London, UK.
authors.forename: Antony N
authors.initials: AN
authors.lastname: Antoniou
mesh_terms: D000818:Animals; D002460:Cell Line; D015796:HLA-B27 Antigen / Q000145:classification* / Q000235:genetics*; D018832:Molecular Chaperones / Q000502:physiology*; D017510:Protein Folding; D055503:Protein Multimerization; D051381:Rats
chemical_list: D015796:HLA-B27 Antigen; D018832:Molecular Chaperones