Structural characterization of globulin from common buckwheat (Fagopyrum esculentum Moench) using circular dichroism and Raman spectroscopy

Raman and far-UV circular dichroism (CD) spectroscopy was used to study the conformation of globulin from common buckwheat (Fagopyrum esculentum Moench) (BWG) under the influence of various buffer environments and heat treatments. Secondary structural analysis of BWG by CD spectroscopy yielded 15.0% α-helical, 25.8% β-sheet, 28.9% β-turn and 30.3% random coil contents. Raman spectrum also showed β-sheets as the major secondary structure in native BWG. Chaotropic salts caused band shifts and intensity changes in Raman amide III vibration, indicating transitions from β-sheet to disordered structure following the lyotropic series of anions. Extreme pHs and several protein structure perturbants led to changes in CD and Raman spectral characteristics, demonstrating protein unfolding and denaturation. Increasing heating time at 100 °C induced the appearance of anti-parallel β-sheet (1235–1237 cm−1) and caused a progressive increase in random coil content, suggesting protein denaturation and aggregation. Both non-covalent and covalent interactions play important roles in stabilizing the conformation of BWG.