The Solvent-Inaccessible Cys67 Residue of HLA-B27 Contributes to T Cell Recognition of HLA-B27/Peptide Complexes

Abstract

Crystallographic studies have suggested that the cysteine at position 67 (Cys67) in the B pocket of the MHC molecule HLA-B*2705 is of importance for peptide binding, and biophysical studies have documented altered thermodynamic stability of the molecule when Cys67 was mutated to serine (Ser67). In this study, we used HLA-B27.Cys67 and HLA-B27.Ser67 tetramers with defined T cell epitopes to determine the contribution of this polymorphic, solvent-inaccessible MHC residue to T cell recognition. We generated these HLA-B27 tetramers using immunodominant viral peptides with high binding affinity to HLA-B27 and cartilage-derived peptides with lower affinity. We demonstrate that the yield of refolding of HLA-B27.Ser67 molecules was higher than for HLA-B27.Cys67 molecules and strongly dependent on the affinity of the peptide. T cell recognition did not differ between HLA-B27.Cys67 and HLA.B27.Ser67 tetramers for the viral peptides that were investigated. However, an aggrecan peptide-specific T cell line derived from an HLA-B27 transgenic BALB/c mouse bound significantly stronger to the HLA-B27.Cys67 tetramer than to the HLA-B27.Ser67 tetramer. Modeling studies of the molecular structure suggest the loss of a SH … π hydrogen bond with the Cys→Ser substitution in the HLA-B27 H chain which reduces the stability of the HLA-B27/peptide complex. These results demonstrate that a solvent-inaccessible residue in the B pocket of HLA-B27 can affect TCR binding in a peptide-dependent fashion.

Two MHC Class I Molecules Associated with Elite Control of Immunodeficiency Virus Replication, Mamu-B*08 and HLA-B*2705, Bind Peptides with Sequence Similarity

“…The 899 peptides tested included the SIV-derived peptides (Supplemental Table I), the Mamu-B*08 endogenous ligands (Table I), and a number of known HLA-B27-restricted T cell epitopes and endogenous ligands described in the literature (15, 50–54) (Table III). We evaluated each peptide for its capacity to bind Mamu-B*08, Mamu-B*03, and HLA-B*2705 (Table IV).…”

Contribution of KIR3DL1/3DS1 to ankylosing spondylitis in human leukocyte antigen-B27 Caucasian populations

“…In addition to their classical antigen-presenting role, it has been described that HLA-B27 are recognised by members of the KIR and leukocyte immunoglobulin-like receptor (ILT) families in both human and animal models. Members of KIR (3DL1 and 3DL2) and ILT (ILT4) are able to bind B27 in both classical β2m/heavy chain (HC) and β2m-free HC homodimers (HC-B27) that are dependent on the presence of Cys67 of the B27 molecule [20-22]. It has been argued that alternative recognition of different forms of HLA-B27 by KIR or ILT could influence their immunomodulatory function and may imply a role in inflammatory disease.…”

Characterization of a Proteasome and TAP-independent Presentation of Intracellular Epitopes by HLA-B27 Molecules

“…A feature of the HLA-B27 molecules is the presence of an unpaired, highly reactive cysteine at position 67. This amino acid has been shown to contribute to the shaping and stability of the B pocket where the primary anchor of the bound peptides, almost invariably an Arg, sits and its substitution promotes faster dissociation and modifies the repertoire of the bound peptides (39,40). Analyzing the C67S B*2705 and B*2709 mutants, we observed a stronger requirement for C67 to stabilize the complexes in the case of B*2705 molecules which, compared with B*2709, display a significant higher ratio between the HC10-reactive (unfolded) and the ME1-reactive (folded) forms on the cell membrane.…”