FT-Raman Spectroscopy as a Tool to Study the Secondary Structures of Wheat Gliadin Proteins

Abstract

Raman spectroscopy is a useful method in biological, biomedical, food, and agricultural studies, allowing the simultaneous examination of various chemical compounds and evaluation of molecular changes occurring in tested objects. The purpose of our research was to explain how the elimination of ω-fractions from the wheat gliadin complex influences the secondary structures of the remaining αβγ-gliadins. To this aim, we analyzed the endosperm of wheat kernels as well as gliadin proteins extracted from two winter wheat genotypes: wasko.gl+ (control genotype containing the full set of gliadins) and wasko.gl− (modified genotype lacking all ω-gliadins). Based on the decomposition of the amide I band, we observed a moderate increase in β-forms (sheets and turns) at the expense of α-helical and random coil structures for gliadins isolated from the flour of the wasko.gl− line. Since ω-gliadins contain no cysteine residues, they do not participate in the formation of the disulfide bridges that stabilize the protein structure. However, they can interact with other proteins via weak, low-energetic hydrogen bonds. We conclude that the elimination of ω-fractions from the gliadin complex causes minor modifications in secondary structures of the remaining gliadin proteins. In our opinion, these small, structural changes of proteins may lead to alterations in gliadin allergenicity.

Does Nitrogen Fertilization Affect the Secondary Structures of Gliadin Proteins in Hypoallergenic Wheat?

“…Conversely, the exposition of this amino acid on the surface of the protein leads to an increase in the disused ratio [ 37 , 38 ]. In the presented results for both tested wheat lines, regardless of nitrogen fertilization, the Tyr doublet was higher than 1.5, which is in line with our previous observation [ 23 ] and also with the results obtained by others researchers [ 39 , 40 ]. However, for wasko.gl+ we observed no influence of nitrogen fertilization on the conformational Tyr modification, for wasko.gl− an increase in the value of the intensity ratio as the response of fertilization was observed.…”

“…The value of the ratio I(855 cm −1 )/I(835 cm −1 ) obtained for both N0 samples of flour from the wheat of wasko.gl+ and wasko.gl− equals 1.86. This result suggests a possible partial exposition of Tyr molecules on the surface of the protein, which is in line with previously obtained results [ 23 ]. However, for wasko.gl+ no changes of the tyrosine doublet under nitrogen fertilization were observed, for wasko.gl− the positive shift from 1.86 for N0 to 2.13 for N120 was detected.…”

“…The authors presented a decrease in the most stable SS ggg bridges and an increase in SS tgg and SS tgt structures after adding dietary fibre to pure gluten samples. Our previous studies proved that the elimination of ω-gliadin fractions from protein clusters could stimulate conformational changes in protein structures [ 23 ]. We found that for wasko.gl+, with a full set of gliadin protein, the SS ggg bonds conformation, typical for more stable forms, was detected in a higher content in the endosperm compared to wasko.gl−.…”

“…We have evidenced a decreased IgE reactivity of the whole gliadin complex due to the elimination of ω- fractions [ 22 ]. Furthermore, we have observed and analysed differences in the gliadins’ secondary structures of wasko.gl− compared to wasko.gl+ control line [ 23 ].…”

Influence of Farming System and Forecrops of Spring Wheat on Protein Content in the Grain and the Physicochemical Properties of Unsonicated and Sonicated Gluten

“…According to Nawrocka et al [29], it shows stronger type I hydrogen bonds (-HN•••O=C-) formed between polypeptide chains in the gluten network, leading to its aggregation. The β-sheet structures are visible at the frequencies of 1634-1640 and 1690-1692 cm −1 with the latter being typical for structures rich in intermolecular hydrogen bonds (antiparallel β-sheets, Aβ-sheet) [30]. For sonicated samples, a higher intensity is observed at 1690 cm −1 , indicating the formation of hydrogen bonds at ultrasound processing.…”