| Affiliations | From the Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute Monash University, and; the Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, Victoria 3800, Australia; the University of Queensland Diamantina Institute, Translational Research Institute, Princess Alexandra Hospital, Brisbane 4102, Australia; the Janssen Research and Development, Pharmaceutical Companies of Johnson & Johnson, Turnhoutseweg 30, B-2340-Beerse, Belgium; the Janssen Research and Development, LLC, Spring House, Pennsylvania 19002, and; From the Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute Monash University, and hugh.reid@monash.edu; From the Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute Monash University, and Jamie.rossjohn@monash.edu; the Institute of Infection and Immunity, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XN, Wales, United Kingdom. | |
| Abstract | The locus is strongly associated with rheumatoid arthritis (RA) susceptibility, whereupon citrullinated self-peptides bind to HLA-DR molecules bearing the shared epitope (SE) amino acid motif. However, the differing propensity for citrullinated/non-citrullinated self-peptides to bind given HLA-DR allomorphs remains unclear. Here, we used a fluorescence polarization assay to determine a hierarchy of binding affinities of 34 self-peptides implicated in RA against three HLA-DRB1 allomorphs (HLA-DRB1*04:01/*04:04/*04:05) each possessing the SE motif. For all three HLA-DRB1 allomorphs, we observed a strong correlation between binding affinity and citrullination at P4 of the bound peptide ligand. A differing hierarchy of peptide-binding affinities across the three HLA-DRB1 allomorphs was attributable to the -chain polymorphisms that resided outside the SE motif and were consistent with sequences of naturally presented peptide ligands. Structural determination of eight HLA-DR4-self-epitope complexes revealed strict conformational convergence of the P4-Cit and surrounding HLA -chain residues. Polymorphic residues that form part of the P1 and P9 pockets of the HLA-DR molecules provided a structural basis for the preferential binding of the citrullinated self-peptides to the HLA-DR4 allomorphs. Collectively, we provide a molecular basis for the interplay between citrullination of self-antigens and HLA polymorphisms that shape peptide-HLA-DR4 binding affinities in RA. | |