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

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 omega-fractions from the wheat gliadin complex influences the secondary structures of the remaining alpha beta gamma-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 omega-gliadins). Based on the decomposition of the amide I band, we observed a moderate increase in beta-forms (sheets and turns) at the expense of alpha-helical and random coil structures for gliadins isolated from the flour of the wasko.gl- line. Since omega-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 omega-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.