Effect of Selected Hofmeister Anions on the Secondary Structure and Dynamics of Wheat Prolamins in Gluten

The effect of selected salts (NaCl, NaBr, NaI) with increasingly chaotropic anions on gluten prolamin secondary structure and dynamics was studied using FT-IR and NMR spectroscopy. FT-IR spectra indicated a small increase in intermolecular beta-sheet structures when gluten samples were incubated with low levels of NaCl and NaBr. The beta-sheet content remained constant with further NaCl addition, but was reduced again with higher NaBr concentrations. NaI addition generally reduced the amount of beta-sheet and increased the amount of beta-turns. From these data, it could be concluded that, in the presence of chaotropic anions, the proteins tended to prefer the beta-turn helix structure characteristic of glutenin subunits in solution. (^1)H-NMR relaxation showed that the molecules were more rigid in 1M NaCl than in pure water, and that the mobility of the prolamins in the presence of 1M NaCl, NaBr, and NaI increased in accordance with the position of the anions in the Hofmeister series. The increase in mobility appeared to be associated with the increase in beta-turn helical structures.