3 years ago

The interplay between citrullination and HLA-DRB1 polymorphism in shaping peptide binding hierarchies in Rheumatoid Arthritis.

Jan Petersen, Anthony W Purcell, Jamie Rossjohn, Anish Suri, Sri H Ramarathinam, Stephen W Scally, Daniel G Baker, Hugh H Reid, Yi Tian Ting, Khai L Loh, Ranjeny Thomas
The HLA-DRB1 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 polarisation 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 b-chain polymorphisms that resided outside the SE motif and were consistent with sequences of naturally presented peptide ligands. Structure determination of eight HLA-DR4-self-epitope complexes revealed strict conformational convergence of the P4-Cit and surrounding HLA b-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.

Publisher URL: http://doi.org/10.1074/jbc.RA117.001013

DOI: 10.1074/jbc.RA117.001013

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