Main Chain Hydrogen Bond Interactions in the Binding of Proline-rich Gluten Peptides to the Celiac Disease-associated HLA-DQ2 Molecule

ArticleinJournal of Biological Chemistry 280(23):21791-6 · July 2005with16 Reads
DOI: 10.1074/jbc.M501558200 · Source: PubMed
Abstract
Binding of peptide epitopes to major histocompatibility complex proteins involves multiple hydrogen bond interactions between the peptide main chain and major histocompatibility complex residues. The crystal structure of HLA-DQ2 complexed with the alphaI-gliadin epitope (LQPFPQPELPY) revealed four hydrogen bonds between DQ2 and peptide main chain amides. This is remarkable, given that four of the nine core residues in this peptide are proline residues that cannot engage in amide hydrogen bonding. Preserving main chain hydrogen bond interactions despite the presence of multiple proline residues in gluten peptides is a key element for the HLA-DQ2 association of celiac disease. We have investigated the relative contribution of each main chain hydrogen bond interaction by preparing a series of N-methylated alphaI epitope analogues and measuring their binding affinity and off-rate constants to DQ2. Additionally, we measured the binding of alphaI-gliadin peptide analogues in which norvaline, which contains a backbone amide hydrogen bond donor, was substituted for each proline. Our results demonstrate that hydrogen bonds at P4 and P2 positions are most important for binding, whereas the hydrogen bonds at P9 and P6 make smaller contributions to the overall binding affinity. There is no evidence for a hydrogen bond between DQ2 and the P1 amide nitrogen in peptides without proline at this position. This is a unique feature of DQ2 and is likely a key parameter for preferential binding of proline-rich gluten peptides and development of celiac disease.
    • "enzyme is abundantly expressed in many tissues and with both intra-and extracellular localization and can convert neutral glutamine residues within Q-X-P sequences into negatively charged glutamate residues, thereby strongly increasing peptide avidity for HLA-DQ2.5 (reviewed in Abadie et al., 2011; Figure 2) or for HLA-DQ8 (Henderson et al., 2007). Finally, proline residues introduce structural constraints that are compatible with peptide binding to HLA-DQ2/8 molecules but not to other MHC class II molecules (Bergseng et al., 2005). As a consequence, HLA-DQ2/8 + dendritic cells can electively activate gluten-specific CD4 + T cells (Figure 2 ). "
    [Show abstract] [Hide abstract] ABSTRACT: Celiac disease (CD) is a chronic enteropathy induced by dietary gluten in genetically predisposed people. The keystone of CD pathogenesis is an adaptive immune response orchestrated by the interplay between gluten and MHC class II HLA-DQ2 and DQ8 molecules. Yet, other factors that impair immunoregulatory mechanisms and/or activate the large population of intestinal intraepithelial lymphocytes (IEL) are indispensable for driving tissue damage. Herein, we summarize our current understanding of the mechanisms and consequences of the undesirable immune response initiated by gluten peptides. We show that CD is a model disease to decipher the role of MHC class II molecules in human immunopathology, to analyze the mechanisms that link tolerance to food proteins and autoimmunity, and to investigate how chronic activation of IEL can lead to T cell lymphomagenesis.
    Article · Jun 2012
    • "Most of these epitopes resist gastrointestinal digestion, and stimulate a T cell response after deamidation by transglutaminase 2 (TG2) [8, 11]. Minor variations in the amino acid sequence of epitopes involved in the disease process were shown to affect their binding within the HLA-DQ2.5 (or -DQ8) binding cleft, and/or the contact of the epitope/ HLA complex with the T cell receptor, suggesting a new treatment of CD based on blocking or modulation of the T cell response by modified immunodominant epitopes, as an G. Di Nardo Department of Pediatrics, Gastroenterology and Liver Unit, University of Rome ''La Sapienza'', Rome, Italy M. Boirivant Department of Infectious Parasitic and Immune Mediated Disease, Istituto Superiore di Sanità, Rome, Italy L. Gazza Á N. Pogna CRA-QCE, Research Unit for Cereal Quality, Rome, Italy alternative to the present therapy based on a life-long gluten-free diet [2, 6, 11]. Sequence QQPQDAVQPF, a natural analog with the same P/Q-rich scaffold and proteolytic resistance of some immunodominant epitopes, was found to prevent prolamininduced proliferation of both intestinal and peripheral blood lymphocytes and enterocyte apoptosis in smallbowel mucosa from CD children121314. "
    [Show abstract] [Hide abstract] ABSTRACT: Celiac disease (CD) is a permanent intolerance to wheat prolamins and related proteins displayed by genetically susceptible individuals. Blocking or modulation of CD-specific T cell response by altered prolamin peptides are currently considered as a potential alternative to the only effective therapy of CD based on a life-long gluten-free diet. Two prolamin peptides, the 9-mer ASRVAPGQQ and the 10-mer GTVGVAPGQQ sequences, were identified by mass spectrometry in the peptic/tryptic digest of prolamins (PTP) from durum wheat (Triticum turgidum ssp. durum) cv. Adamello, and investigated for their ability to preclude the stimulation of CD-specific mucosal T cells by gluten proteins. Gluten-specific polyclonal intestinal T cell lines from five CD children (mean age 5 years) were exposed to 50 microg/ml of a deamidated PTP from whole flour of common wheat (T. aestivum) cv. San Pastore, and tested for proliferation and production of interferon-gamma (INF-gamma) and interleukin 10 (IL-10). The same experiment was performed in the presence of 20 microg/ml of the 9-mer or the 10-mer peptide. T cells exposed to PTP showed a threefold increase in proliferation and INF-gamma production, and a significant (P <or= 0.05) reduction in IL-10 secretion as compared with control cells incubated with the culture medium. Addition of either the 9-mer or the 10-mer peptide to PTP downregulated T cell proliferation and INF-gamma production, and caused a significant (P <or= 0.05) increase in IL-10 secretion. The T cell reactivity elicited by PTP is precluded by both the 9-mer and the 10-mer sequence, suggesting that over-expression of these proteolytically stable peptides may result in a wheat flour with reduced toxicity for CD patients.
    Full-text · Article · Nov 2009
    • "The characterization of such a strong interaction could be helpful to design new lead structures for high affinity HLA- DQ2 blockers. Such reagents have been discussed in the treatment of celiac disease to inhibit HLA-DQ2-rectricted presentation of gluten derived epitopes (Bergseng et al. 2005; Xia et al. 2006 Xia et al. , 2007). In the presence of HLA-DM, binding of the known HLA-DQ2 ligand P198 to the isolated sDQ2/DCB-45 complex increased. "
    [Show abstract] [Hide abstract] ABSTRACT: We here describe that soluble HLA-DQ2 (sDQ2) molecules, when expressed in Drosophila melanogaster S2 insect cells without a covalently tethered peptide, associate tightly with the D. melanogaster calcium binding protein DCB-45. The interaction between the proteins is stable in S2 cell culture and during affinity purification, which is done at high salt concentrations and pH 11.5. After affinity purification, the sDQ2/DCB-45 complex exists in substantial quantities next to a small amount of free heterodimeric sDQ2 and large amounts of aggregated sDQ2 free of DCB-45. Motivated by the stable complex formation and our interest in the development of reagents which inhibit HLA-DQ2 peptide binding, we have further characterized the sDQ2/DCB-45 interaction. Several lines of evidence indicate that an N-terminal fragment of DCB-45 is involved in the interaction with the peptide binding groove of sDQ2. Further mapping of this fragment of 54 residues identified a pentadecapeptide with high affinity for sDQ2 which may serve as a lead compound for the design of HLA-DQ2 blockers.
    Full-text · Article · Dec 2008
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