Design, synthesis and evaluation of gluten peptide analogues as inhibitors of the HLA/DQ8-mediated celiac immune response

Abstract

The immune response induced by gluten is the result of molecular mechanisms involving gliadin peptides, DQ2 or DQ8 glycoproteins, and the interaction with T lymphocyte receptors. DQ8-glia-α1 is an immunodominant peptide present in gliadin from wheat Triticum spelta that interacts with the DQ8 protein, as proven through transgenic mouse models. The research was carried out by performing a computational analysis aimed at finding antagonistic peptides of the DQ8-glia-α1 peptide, i.e. peptides obtained by varying its amino acids to maintain or even enhance the binding towards DQ8 and at the same time to prevent an immune response by a reduced interaction with the T lymphocyte receptors. Crystallographic structures of DQ8 and three different T-cell receptors were taken as experimental starting systems, the peptide–protein interaction was modelled by molecular dynamics simulations and molecular interaction field calculations, and the optimal mutations of the peptide sequence were identified by using multivariate analysis. The method provided a list of nine immunodominant peptide candidates, which were produced by chemical synthesis and validated by tests on transgenic mice. The results showed that immunization with the peptide (DQ8-glia-α1, designated M1) induced in vitro antigen-specific secretion of IFN-γ restricted to the M1 peptide alone. M1 also stimulated antigen-specific secretion of the regulatory cytokine IL-10. A peptide (i.e., M10) was identified as a potential therapeutic molecule for down-regulating the inflammatory condition triggered by the DQ8-glia-α1 immunodominant peptide in CD.