Polypeptide components of oligomeric legumin-like thiamin-binding protein from buckwheat seeds characterized by partial amino acid sequencing and photoaffinity labeling

Epitope mapping and identification on a 3D model built for the tartary buckwheat allergic protein TBb

Allergic protein TBb, a major allergen in tartary buckwheat, was divided into four epitope-containing fragments and was named F1, F2, F3, and F4, respectively. Results of immunological assays revealed that F2 had the strongest IgE-binding activity to patient's sera, which indicated that it might contain the linear IgE-binding epitope of TBb. According to the results of sequence analysis and molecular modeling of tartary buckwheat allergen, three mutants of F2 gene (R139A, R141A, and D144A) were reconstructed using site-directed mutagenesis, and each mutant was expressed in Escherichia coli BL21 (DE3). Following purification by Ni(2+) affinity chromatography, enzyme-linked immunosorbent assay and dot blot were performed for wild-type F2 and its mutants using sera from buckwheat-allergic patients and a negative control (non-allergic patient). Results showed that mutants R139A and D144A had weaker IgE-binding activity to patient's sera than wild-type F2, implying that Arg(139) and Asp(144) might be involved in the allergic activity of TBb. However, R141A had the weakest IgE-binding activity, suggesting that Arg(141) may be the critical amino acid of TBb. This is the first report on the epitope mapping and identification of TBb. Our findings will contribute to the production of TBb hypoallergens and to allergen-specific immunotherapy for tartary buckwheat allergy.

Thiamine binding and metabolism in germinating seeds of selected cereals and legumes

The basic characteristics of thiamine metabolism in germinating seeds of maize (Zea mays), oat (Avena sativa), faba bean (Vicia faba) and garden pea (Pisum sativum) are presented with a special emphasis of a possible thiamine storage function of seed thiamine-binding proteins (TBPs). Seeds were germinated for 6 d in the dark. Thiamine-binding activity in seeds decreased during germination by 50% in cereals and by 30% in legumes. The degradation of TBPs was also detected by polyacrylamide gel electrophoresis. The total thiamine content decreased rapidly to 20-40% of the initial value in cereal seeds during first 3 d of germination while in legume seeds thiamine content started changing from the fourth day and dropped by 50% at the sixth day. A composite pattern was found for the changes in thiamine pyrophosphate (TPP) contribution to total thiamine during seed germination. A peak of the coenzyme percentage was usually detected at the second day of germination. Another gain of TPP was often seen toward the sixth day of germination. The activity of thiamine pyrophosphokinase (EC 2.7.6.2) was high in resting legume seeds and did not significantly change during germination. In contrast, the low activity of this thiamine-activating enzyme in cereal seeds progressively increased during germination. Thiamine phosphate synthase (EC 2.5.1.3) was also detected in seeds and was shown to contribute significantly to the balance of thiamine compounds during seed germination.