Conformational and thermal properties of phaseolin, the major storage protein of red kidney bean (Phaseolus vulgaris L.).
BACKGROUND
A previous study of various functional and physicochemical properties of phaseolin indicated good potential of phaseolin for application in food formulations in view of its excellent functional properties. The aim of the present study was to explore the conformational and thermal properties of phaseolin in the presence of protein structural perturbants by intrinsic fluorescence emission spectroscopy and differential scanning calorimetry. Raman spectroscopy was also used to characterise the secondary structures of phaseolin.


RESULTS
The Raman spectrum of phaseolin indicated that β-sheets and random coils were the major secondary structures. Intrinsic fluorescence emission spectroscopy confirmed the structural peculiarity and compactness of phaseolin, as evidenced by the absence of any shift in emission maximum (λ(max)) in the presence of structural perturbants such as sodium dodecyl sulfate (SDS), guanidine hydrochloride, urea and dithiothreitol (DTT). Increasing NaCl concentration enhanced the thermal stability of phaseolin. Addition of chaotropic salts (1 mol L(-1)) caused progressive decreases in thermal stability following the lyotropic series of anions. Decreases in thermal denaturation temperature (T(d)) and enthalpy change (ΔH) were observed in the presence of protein perturbants such as SDS, urea and ethylene glycol, indicating partial denaturation and a decrease in thermal stability. DTT and N-ethylmaleimide had little effect on the thermal properties of phaseolin, confirming that phaseolin, a 7S globulin, is devoid of inter-polypeptide disulfide bonds.


CONCLUSIONS
The data presented here demonstrate the contributions of hydrophobic and electrostatic interactions and hydrogen bonding to the conformational stability of phaseolin.
Yin
Shou-Wei
SW
Department of Food Science and Technology, South China University of Technology, Guangzhou, China.
Tang
Chuan-He
CH
Wen
Qi-Biao
QB
Yang
Xiao-Quan
XQ
D057927:Hydrophobic and Hydrophilic Interactions; D027805:Phaseolus / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D011487:Protein Conformation; D012639:Seeds / Q000737:chemistry*; D055672:Static Electricity
D010940:Plant Proteins; C048826:phaseolin protein, Phaseolus vulgaris