Polymorphisms in the F Pocket of HLA-B27 Subtypes Strongly Affect Assembly, Chaperone Interactions, and Heavy-Chain Misfolding

David B. Guiliano, Helen North, Eleni Panayoitou, Elaine C. Campbell, Kirsty Mchugh, Fiona G. M. Cooke, Marine Silvestre, Paul Bowness, Simon J. Powis, Antony N. Antoniou

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

Objective
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.

Methods
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.

Results
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.

Conclusion
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.
Original languageEnglish
Pages (from-to)610-621
Number of pages12
JournalArthritis & Rheumatology
Volume69
Issue number3
Early online date9 Oct 2016
DOIs
Publication statusPublished - 1 Mar 2017

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