Conformational study of globulin from rice (Oryza sativa) seeds by Fourier-transform infrared spectroscopy

The conformation of rice globulin (10%, w/v, in deuterated phosphate buffer, pD 7.4) under the influence of pH, chaotropic salts, several protein structure perturbants and heat treatments was studied by Fourier-transform infrared (FTIR) spectroscopy. Rice globulin exhibited seven major bands in the region of 1700-1600 cm−1 and the spectrum suggests high α-helical content with large quantities of β-sheet and β-turn structures. Highly acidic and alkaline pH conditions induced changes in band intensity attributed to intermolecular β-sheet structure (1681 and 1619 cm−1). Addition of chaotropic salts led to progressive changes in band intensity, following the lyotropic series of anions, whereas several protein structure perturbants caused shifts in band positions. Heating at increasing temperature led to progressive decreases in α-helical content and increases in random coil structures, suggesting protein denaturation. This was accompanied by intensity increases in the intermolecular β-sheet transitions.