Identification of transglutaminase‐mediated deamidation sites in a recombinant α‐gliadin by advanced mass‐spectrometric methodologies

Abstract

Celiac disease is a permanent immune-mediated food intolerance triggered by ingestion of wheat gliadins in genetically susceptible individuals. It has been reported that tissue transglutaminase plays an important role in the onset of celiac disease by converting specific glutamine residues within gliadin fragments into glutamic acid residues. This process increases binding affinity of gliadin peptides to HLA-DQ2/DQ8 molecules, thus enhancing the immune response. The aim of the present study was to achieve a detailed structural characterization of modifications induced by transglutaminase on gliadin peptides. Therefore, structural analyses were carried out on a recombinant ␣-gliadin and on a panel of 26 synthetic peptides, overlapping the complete protein sequence. Modified glutamine residues were identified by means of advanced mass-spectrometric methodologies on the basis of MALDI-TOF-MS and tandem mass spectrometry. Results led to the identification of 19 of 94 glutamine residues present in the recombinant ␣-gliadin, which were converted into glutamic acid residues by a transglutaminase-mediated reaction. This allowed us to achieve a global view of the modifications induced by the enzyme on this protein. Furthermore, results gathered could likely be utilized as relevant information for a better understanding of processes leading to T-cell recognition of gliadin peptides involved in celiac disease.Keywords: Gliadin; transglutaminase; mass spectrometry; celiac disease; posttranslational modifications Celiac disease (or gluten-sensitive enteropathy, CD) is a permanent intolerance to gluten, which is a complex mixture of storage proteins (glutenins and gliadins) found in wheat and in other grains like barley, rye, and oats. In many genetically susceptible individuals, dietary exposure to gluten induces an inflammatory response, causing destruction of the villous structure of the small intestine (Marsh 1992). Celiac disease is strongly associated with HLA-DQ2 (A1*0501, B1*0201) and HLA-DQ8 (A*0301, B*0302; Spurkland et al. 1997). In fact, gluten-specific HLA-DQ2 and/or HLA-DQ8-restricted CD4 + T lymphocytes were isolated from small intestinal biopsies of CD patients and gliadin-specific T-cell clones were prepared and tested (Lundin et al. 1993;van der Wal et al. 1998a). HLA class II molecules mediate the presentation of gliadin-derived peptides to T-cell leading to T-cell stimulation. CD is also characterized by secretion of specific antibodies against gliadin and tissue transglutaminase (tTGase), and in fact, the presence of antibodies specific for tTGase in serum from celiac Reprint requests to: Rosa Anna Siciliano, Centro di Spettrometria di Massa Proteomica e Biomolecolare, Istituto di Scienze dell'Alimentazione del CNR, via Roma 52, 83100 Avellino, Italy; e-mail: rsiciliano@isa.cnr.it; fax: 39-0825-781585.Abbreviations: CD, celiac disease; CID, collision induced dissociation; MALDI-TOF-MS, matrix-assisted laser desorption ionization-time of flight-mass spectrometry; MS/MS, tandem mass spectrometry; na...

The Preferred Substrates for Transglutaminase 2 in a Complex Wheat Gluten Digest Are Peptide Fragments Harboring Celiac Disease T-Cell Epitopes

“…Two of them, peptide #19 and peptide #25, elicited dose-dependent T-cell responses in one or more T-cell lines. Peptides #8 and #9, which are found in the well-investigated α2-gliadin protein, have also been reported as substrates for TG2 [25] and their sequences suggest that they may bind to HLA-DQ2.5. In keeping with previous findings [12] , [26] , our results indicate however that these peptides do not harbor T-cell epitopes.…”

Mass production of active recombinant Chryseobacterium proteolyticum protein glutaminase in Escherichia coli using a sequential dual expression system and one‐step purification

“…20,21 Meanwhile it has also been found that gliadin is made up of a high percentage of glutamine residues (30-40%). 22 It is possible that the modification of glutamine (Q) to glutamate (E) in the epitope regions may lower the allergenicity of gliadin. Yong et al proved that the allergenicity of deamidated wheat gluten remarkably decreases as the deamidation time is prolonged.…”

Biochemical and structural characterization of mammalian‐like purine nucleoside phosphorylase from the Archaeon Pyrococcus furiosus

“…Protein samples and peptide mixtures obtained from enzymatic or chemical digestion were analyzed on a MALDI‐TOF mass spectrometer Voyager DE TM PRO (Applied Biosystems, Foster City, CA, USA), as already described [57]. In the m / z range 4000–40000 mass spectra were acquired in linear positive‐ion mode and calibrated using as internal standards the average double and singly charged peaks originated from cytochrome c ( m / z 6181.05 and 12 361.10, respectively).…”

“…Tandem mass spectrometric analyses performed on a hybrid quadruple ⁄ orthogonal time of flight instrument (QStar Pulsar, Applied Biosystems) equipped with nanospray source, were carried out as already described [57].…”