New chelation strategy allows for quick and clean 99mTc-labeling of synthetic peptides.

Analogues of bombesin have been synthesized in which a N2S2 (bis-mercaptoacetyl functionalized diaminopropionic acid) or a N3S (mercaptoacetyl-Gly-Gly-Gly) radiometal-chelating center has been incorporated that allows radiolabeling of these peptides with 99mTc without the need for conjugation or harsh reaction conditions. A mild radiolabeling is possible by using an acetyl-moiety as sulfur protecting group, which can be removed by mild hydroxylamine-treatment at room temperature before radiolabeling. Retained receptor binding is demonstrated in competitive binding experiments with 99mTc-radiolabeled peptides and PC-3 cells with bombesin receptors.

Characterization of cereal toxicity for celiac disease patients based on protein homology in grains.

BACKGROUND AND AIMS: Celiac disease is caused by T-cell responses to wheat gluten-derived peptides. The presence of such peptides in other widely consumed grains, however, has hardly been studied. METHODS: We have performed homology searches to identify regions with sequence similarity to T-cell stimulatory gluten peptides in the available gluten sequences: the hordeins of barley, secalins of rye, and avenins of oats. The identified peptides were tested for T-cell stimulatory properties. RESULTS: With 1 exception, no identical matches with T-cell stimulatory gluten peptides were found in the other grains. However, less stringent searches identified 11 homologous sequences in hordeins, secalins, and avenins located in regions similar to those in the original gluten proteins. Seven of these 11 peptides were recognized by gluten-specific T-cell lines and/or clones from patients with celiac disease. Comparison of T-cell stimulatory sequences with homologous but non-T-cell stimulatory sequences indicated key amino acids that on substitution either completely or partially abrogated the T-cell stimulatory activity of the gluten peptides. Finally, we show that single nucleotide substitutions in gluten genes will suffice to induce these effects. CONCLUSIONS: These results show that the disease-inducing properties of barley and rye can in part be explained by T-cell cross-reactivity against gluten-, secalin-, and hordein-derived peptides. Moreover, the results provide a first step toward a rational strategy for gluten detoxification via targeted mutagenesis at the genetic level.

Specificity of tissue transglutaminase explains cereal toxicity in celiac disease.

Celiac disease is caused by a selective lack of T cell tolerance for gluten. It is known that the enzyme tissue transglutaminase (tTG) is involved in the generation of T cell stimulatory gluten peptides through deamidation of glutamine, the most abundant amino acid in gluten. Only particular glutamine residues, however, are modified by tTG. Here we provide evidence that the spacing between glutamine and proline, the second most abundant amino acid in gluten, plays an essential role in the specificity of deamidation. On the basis of this, algorithms were designed and used to successfully predict novel T cell stimulatory peptides in gluten. Strikingly, these algorithms identified many similar peptides in the gluten-like hordeins from barley and secalins from rye but not in the avenins from oats. The avenins contain significantly lower percentages of proline residues, which offers a likely explanation for the lack of toxicity of oats. Thus, the unique amino acid composition of gluten and related proteins in barley and rye favors the generation of toxic T cell stimulatory gluten peptides by tTG. This provides a rationale for the observation that celiac disease patients are intolerant to these cereal proteins but not to other common food proteins.