HLA–B27 heavy chains distinguished by a micropolymorphism exhibit differential flexibility

Abstract

Objective. Although the products of the HLA subtypes B*2705 and B*2709 differ only in residue 116 (Asp versus His) within their peptide-binding grooves, they are differentially associated with inflammatory rheumatic diseases such as ankylosing spondylitis (AS): B*2705 occurs in AS patients, whereas B*2709 is only rarely encountered. The reasons for this distinct association are still unclear but could include subtypespecific conformational and dynamic properties of these antigens. The present study was undertaken to investigate structural and dynamic differences between B*2705 and B*2709 and their possible relationship to subtypespecific disease association.Methods. The membrane-distal segments of the B*2705 and B*2709 heavy chains were expressed in vitro and reconstituted together with ␤ 2 -microglobulin and a peptide. HLA-B27 complexes loaded with 2 self peptides (TIS [RRLPIFSRL] and pVIPR [RRKWRRWHL]) and a sequence-related viral peptide (pLMP2 [RRRWRRLTV]) were studied by isotope-edited infrared spectroscopy to detect differences in their structure and flexibility at physiologic temperature.Results. Our analyses revealed the existence of subtype-specific conformational differences between the 2 HLA-B27 heavy chains at physiologic temperature, which are undetectable using x-ray crystallography. Irrespective of the bound peptide, the heavy chain of the B*2705 complex exhibited higher conformational flexibility than the B*2709 heavy chain.Conclusion. The present study demonstrates the existence of previously undetected systematic conformational and dynamic differences between the heavy chains of the 2 HLA-B27 subtypes. Since effector cell recognition of cells expressing HLA antigens is dependent on the dynamic properties of the interacting cell surface molecules, this HLA-B27 subtype-specific heavy chain flexibility could have a role in the distinct association of HLA-B27 subtypes with spondylarthritides.

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

“…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]).…”

“…We envisage that these water clusters influence an up-and down movement of the peptide whose main chain is suspended in a highly conserved fashion between the two α-helices of the binding groove, involving residues Asp77 and Trp147. In turn, this movement will lead to an inward or outward movement of the α-helices which could not only influence the IR spectrum of a given subtype, but also the interaction of the latter with effector cells (Fabian et al, 2010). Advanced mass spectrometry techniques might eventually tell us which part of the HLA-B27 HC is affected by the subtype-specific changes.…”

“…One particularly interesting and very novel aspect of peptide-MHC complexes that may also play a role in autoimmune phenomena refers to the intrinsic HC flexibility that is greater in B*27:05 than in B*27:09, independent of the conformation or the sequence of a peptide ( [Fabian et al, 2008], [Fabian et al, 2010] and [Fabian et al, 2011]). We do not know whether this is also a property of other disease-related HC, and how this property might, e.g., affect the binding of TCR.…”

“…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.…”