Modulation of Natural HLA-B*27:05 Ligandome by Ankylosing Spondylitis-associated Endoplasmic Reticulum Aminopeptidase 2 (ERAP2).

The HLA-B*27:05 allele and the endoplasmic reticulum-resident aminopeptidases are strongly associated with AS, a chronic inflammatory spondyloarthropathy. This study examined the effect of ERAP2 in the generation of the natural HLA-B*27:05 ligandome in live cells. Complexes of HLA-B*27:05-bound peptide pools were isolated from human ERAP2-edited cell clones, and the peptides were identified using high-throughput mass spectrometry analyses.

Functional interaction of the ankylosing spondylitis-associated endoplasmic reticulum aminopeptidase 1 polymorphism and HLA-B27 in vivo.

The association of ERAP1 with ankylosing spondylitis (AS)1 among HLA-B27-positive individuals suggests that ERAP1 polymorphism may affect pathogenesis by altering peptide-dependent features of the HLA-B27 molecule. Comparisons of HLA-B*27:04-bound peptidomes from cells expressing different natural variants of ERAP1 revealed significant differences in the size, length, and amount of many ligands, as well as in HLA-B27 stability. Peptide analyses suggested that the mechanism of ERAP1/HLA-B27 interaction is a variant-dependent alteration in the balance between epitope generation and destruction determined by the susceptibility of N-terminal flanking and P1 residues to trimming.

Mutational analysis reveals a complex interplay of peptide binding and multiple biological features of HLA-B27.

Molecular polymorphism influences the strong association of HLA-B27 with ankylosing spondylitis through an unknown mechanism. Natural subtypes and site-directed mutants were used to analyze the effect of altering the peptide-binding site of this molecule on its stability, interaction with tapasin, folding, and export. The disease-associated subtypes B*2705, B*2702, and B*2704 showed higher thermostability at 50 °C than all other subtypes and mutants, except some mimicking B*2702 polymorphism.

Presentation of cytosolically stable peptides by HLA-B27 is not dependent on the canonic interactions of N-terminal basic residues in the A pocket.

HLA-B27 binds peptides with R at position 2. Additionally, a substantial fraction of the HLA-B27-bound peptide repertoire has basic residues at position 1. It is unclear whether this is determined by structural complementarity with the A pocket of the peptide-binding site, by the increased availability of peptides with dibasic N-terminal sequences resulting from their cytosolic stability, or both.

Disparate folding and stability of the ankylosing spondylitis-associated HLA-B*1403 and B*2705 proteins.

Objective: To investigate the folding, assembly, maturation, and stability of HLA-B*1402 and B*1403, which differ by 1 amino acid change and are differentially associated with ankylosing spondylitis (AS), and to compare these features with those of B*2705.

Methods: Stable transfectants expressing B*1402, B*1403, and B*2705 were used. Folding rates were estimated from the ratio of unfolded heavy chains to folded heavy chains that had been immunoprecipitated with specific antibodies in pulse-chase experiments.