Main chain hydrogen bond interactions in the binding of proline-rich gluten peptides to the Celiac disease-associated HLA-DQ2 molecule
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.
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ABSTRACT: This review discusses mechanisms that link allelic variants of major histocompatibility complex (MHC) class II molecules (MHCII) to immune pathology. We focus on HLA (human leukocyte antigen)-DQ (DQ) alleles associated with celiac disease (CD) and type 1 diabetes (T1D) and the role of the murine DQ-like allele, H2-Ag7 (I-Ag7 or Ag7), in murine T1D. MHCII molecules bind peptides, and alleles vary in their peptide-binding specificity. Disease-associated alleles permit binding of disease-inducing peptides, such as gluten-derived, Glu-/Pro-rich gliadin peptides in CD and peptides from islet autoantigens, including insulin, in T1D. In addition, the CD-associated DQ2.5 and DQ8 alleles are unusual in their interactions with factors that regulate their peptide loading, invariant chain (Ii) and HLA-DM (DM). The same alleles, as well as other T1D DQ risk alleles (and Ag7), share nonpolar residues in place of Asp at β57 and prefer peptides that place acidic side chains in a pocket in the MHCII groove (P9). Antigen-presenting cells from T1D-susceptible mice and humans retain CLIP because of poor DM editing, although underlying mechanisms differ between species. We propose that these effects on peptide presentation make key contributions to CD and T1D pathogenesis.Expert Reviews in Molecular Medicine 07/2012; 14:e15. DOI:10.1017/erm.2012.9 · 5.91 Impact Factor
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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.Immunity 06/2012; 36(6):907-19. DOI:10.1016/j.immuni.2012.06.006 · 19.75 Impact Factor
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ABSTRACT: Cereal Chem. 85(1):1–13 Celiac disease (CD) is an inflammatory disorder of the upper small in-testine triggered by the ingestion of wheat, rye, barley, and possibly oat products. The clinical feature of CD is characterized by a flat intestinal mucosa with the absence of normal villi, resulting in a generalized malabsorption of nutrients. The prevalence of CD among Caucasians is now thought to be in a range of 1:100–300. There is a strong genetic asso-ciation with human leukocyte antigens (HLA-)DQ2 and DQ8 and cur-rently unknown non-HLA genes. During the last decade, intense bio-chemical studies have contributed to substantial progress in understanding the general principles that determine the pathogenesis of CD. The precipi-tating factors of toxic cereals are the storage proteins, termed gluten in the field of CD (gliadins and glutenins of wheat, secalins of rye, and hordeins of barley). There is still disagreement about the toxicity of oat avenins. The structural features unique to all CD toxic proteins are sequence domains rich in Gln and Pro. The high Pro content renders these proteins resistant to complete proteolytic digestion by gastrointestinal enzymes. Consequently, large Pro-and Gln-rich peptides are cumulated in the small intestine and reach the subepithelial lymphatic tissue. Depending on the amino acid sequences, these peptides can induce two different immune responses. The rapid innate response is characterized by the secretion of the cytokine interleukin-15 and the massive increase of intraepithelial lymphocytes. The slower adaptive response includes the binding of gluten peptides (native or partially deamidated by tissue transglutaminase) to HLA-DQ2 or -DQ8 of antigen presenting cells and the subsequent stimu-lation of T-cells accompanied by the release of proinflammatory cyto-kines such as interferon-γ and the activation of matrix metalloproteinases. Both immune responses result in mucosal destruction and epithelial apop-tosis. Additionally, stimulated T-cells activate B-cells that produce serum IgA and IgG antibodies against gluten proteins (antigen) and tissue trans-glutaminase (autoantigen). These antibodies can be used for noninvasive screening tests to diagnose CD. The current essential therapy of CD is a strict lifelong adherence to gluten-free diet. Dietetic gluten-free foods produced for CD patients underlie the regulations of the Codex Alimen-tarius Standard for Gluten-Free Foods. The "Draft Revised Codex Stan-dard" edited in March 2006 proposes a maximum level of 20 mg of glu-ten/kg for naturally gluten-free foods (e.g., based on rice or corn flour) and 200 mg/kg for foods rendered gluten-free (e.g., wheat starch). Nu-merous analytical methods for gluten determination have been developed, mostly based on immunochemical assays, mass spectrometry, or poly-merase chain reaction. So far, only two enzyme-linked immunosorbent assays have been successfully ring-tested and are commercially available. During the last decade, future strategies for prevention and treatment of CD have been proposed. They are based on the removal of toxic epitopes by enzymatic degradation or gene engineering and on blocking parts of the immune system. However, any alternative treatment should have a safety profile competitive with gluten-free diet.Cereal Chemistry 01/2008; 85. DOI:10.1094/CCHEM-85-1-0001 · 1.06 Impact Factor