Structural studies of wheat flour glutenin polymers by CD spectroscopy

A dissolution procedure of unreduced glutenin polymers of three wheat flour varieties (WRU 6981, Alisei 1, and Alisei 2) by sonication in the presence of SDS (sodium dodecyl sulphate), after the elimination of albumins, globulins, and gliadins, was achieved, and the molecular weight distribution of glutenin polymers obtained by this method was measured by matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. A structural study by CD spectroscopy at different temperatures of WRU 6981 glutenin polymer and of 1Ax1 high-M(r) (relative molecular mass) glutenin subunit, which is the only high-M(r) subunit contained in WRU 6981 flour, was undertaken to understand if the information obtained from the single subunit were applicable to the total polymer. CD spectroscopy also has been employed to study the glutenin polymers obtained by Alisei 1 and Alisei 2 wheat flours; Alisei 1 biotype contained 1Bx7 and 1Dx2+1Dy12 high-M(r) subunits, whereas the Alisei 2 biotype contained only 1Bx7 and 1Dy12 subunits. A conformational study was undertaken by CD spectroscopy at different temperatures and in the presence of some chemical denaturant agents, such as urea and sodium dodecyl sulphate, in order to obtain information about their intrinsic stability and to verify if the 1Dx2 subunit presence determined a different structural behavior between Alisei 1 and Alisei 2 polymers. MALDI-TOF mass spectrometric experiments showed that the glutenin polymers molecular weights were in the mass range of 500000-5000000. CD spectra indicated that a single conformational state did not predominate in the temperature range studied but equilibrium between two distinct conformational states existed; moreover, all the changes induced by urea and by SDS followed a multistep transition process.

Conformational studies of wheat flour high relative molecular mass glutenin subunits by circular dichroism spectroscopy

Conformational studies of 1Dx2, 1Bx7, and 1Dy12 high relative molecular mass glutenin subunits, extracted from Alisei 1 flour, are reported. Circular dichroism (CD) spectroscopy is employed to study their conformational polymorphism induced by urea and by urea in the presence of 1% sodium dodecyl sulfate (SDS). The CD spectra indicate that SDS promotes ordered structures. The addition of urea to the SDS-acetate solution of 1Dx2, 1Bx7, and 1Dy12 subunits eliminates the effect of SDS. Its addition to the acetate solution of proteins induces conformational transitions to form a poly-L-proline II-like structure. All the changes induced by urea follow a multistep transition process that is typical of proteins consisting of different domains.