New insight into the solution structures of wheat gluten proteins from Raman optical activity

Vibrational Raman optical activity (ROA) spectra of the wheat proteins alpha-gliadin (A-gliadin), omega-gliadin, and a 30 kDa peptide called T-A-1 from the high molecular weight glutenin subunit (HMW-GS) Dx5 were measured to obtain new information about their solution structures. The spectral data show that, under the conditions investigated, A-gliadin contains a considerable amount of hydrated alpha-helix, most of which probably lies within a relatively structured C-terminal domain. Smaller quantities of beta-structure and poly(l-proline) II (PPII) helix were also identified. Addition of methanol was found to increase the alpha-helix content at the expense of some of the beta and PPII structure. In comparison, omega-gliadin and the T-A-1 peptide were found to consist of large amounts of well-defined PPII structure with some turns but no alpha-helix. The results for the T-A-1 peptide are in agreement with a model in which HMW-GS are extended but not highly rigid. Application of a pattern recognition technique, based on principal component analysis (PCA), to the ROA spectra reinforces these conclusions.