Influence of inflammation‐related changes on conformational characteristics of HLA‐B27 subtypes as detected by IR spectroscopy

Abstract

Inflammatory processes are accompanied by the post‐translational modification of certain arginine residues to yield citrulline, and a pH decrease in the affected tissue, which might influence the protonation of histidine residues within proteins. We employed isotope‐edited IR spectroscopy to investigate whether conformational features of two human major histocompatibility antigen class I subtypes, HLA‐B*2705 and HLA‐B*2709, are affected by these changes. Both differ only in residue 116 (Asp vs. His) within the peptide‐binding grooves, but are differentially associated with inflammatory rheumatic disorders. Our analyses of the two HLA‐B27 subtypes in complex with a modified self‐peptide containing a citrulline RRKWURWHL (U = citrulline) revealed that the heavy chain is more flexible in the HLA‐B*2705 subtype than in the HLA‐B*2709 subtype. Together with our previous studies of HLA‐B27 subtypes complexed with the unmodified self‐peptide RRKWRRWHL, these findings support the existence of subtype‐specific conformational features of the heavy chains under physiological conditions, which are undetectable by X‐ray crystallography and exist irrespective of the sequence of the bound peptide and its binding mode. They might thus influence antigenic properties of the respective HLA‐B27 subtype. Furthermore, a decrease in the pH from 7.5 to 5.6 during the analyses had an influence only on HLA‐B*2709 complexed with the unmodified self‐peptide, where His116 is not contacted by any peptide side chain. This permits us to conclude that histidines, and in particular His116, influence the stability of MHC:peptide complexes. The conditions prevailing in inflammatory environments in vivo might thus also exert an impact on selected conformational features of HLA‐B27:peptide complexes. Structured digital abstract http://www.uniprot.org/uniprot/P03989 and http://www.uniprot.org/uniprot/P32241 http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407 by http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0013 (http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-8144492).

Peptide Modulation of Class I Major Histocompatibility Complex Protein Molecular Flexibility and the Implications for Immune Recognition*

“…Indeed, with HLA-A2, the mobility of the region that undergoes a structural change upon binding of the A6 TCR was shown to vary with different peptides (10). This may not be a unique observation as similar effects are believed to contribute to differential T cell recognition of native and modified MART-1 peptides (6), and MHC flexibility can be altered by micropolymorphisms (7,14,15). As demonstrated by the A6 TCR, peptide-dependent MHC dynamics can impact TCR recognition by altering the barriers for conformational adjustments, influencing the entropic costs for receptor binding and shifting the populations of binding-competent states.…”

HLA class I-associated diseases with a suspected autoimmune etiology: HLA-B27 subtypes as a model system

“…We also determined the first structure (Hülsmeyer et al, 2005a) of an MHC molecule in complex with a recombinant mAb exhibiting peptide-specific reactivity (Chames et al, 2000). Furthermore, we found that the intrinsic flexibility of the B*27:05 heavy chain (HC) is independent of both the sequence as well as the conformation of a bound peptide, but is more pronounced than that exhibited by the HC of the B*27:09 subtype ( [Fabian et al, 2008], [Fabian et al, 2010] and [Fabian et al, 2011]). These are the first results that reveal a correlation between dynamic properties of MHC molecules and a disease.…”

“…2G). Not only Asp116, but also Asp74 and Asp77 on the α1-helix of the HC are contacted via salt bridges, and there are multiple hydrogen bonds to the guanidinium moiety as well as several hydrophobic contacts with HC residues that flank the F pocket (Loll et al, 2011). The most notable feature resulting from this extensive network of atomic contacts between pArg9 and F pocket residues is the exclusion of pArg5 from interactions with Asp116.…”

“…Independent of the peptide, the IR spectroscopic data indicate that the β 2 m molecules of all eight complexes exhibit virtually indistinguishable conformational and dynamic properties. However, the B*27:05 HC was found to display a higher degree of conformational flexibility at physiological temperature than the B*27:09 HC, irrespective of the bound peptide ( [Fabian et al, 2008], [Fabian et al, 2010] and [Fabian et al, 2011]). An example for the type of data obtained with the peptides pVIPR and TIS is provided in Fig.…”

“…For IR spectroscopy, the light chain of MHC class I complexes, β 2 m, was labelled in vivo with 13 C and then complexed with unlabelled HLA-B27 HC and selected peptides in vitro ( [Fabian et al, 2008], [Fabian et al, 2010] and [Fabian et al, 2011]). Conversely, for fluorescence spectroscopic experiments, unlabelled HLA-B27 HC and β 2 m were reconstituted with peptides carrying a fluorescent marker ( [Pöhlmann et al, 2004], , [Winkler et al, 2007] and [Narzi et al, 2008]).…”