چكيده لاتين
The use of artificial sweeteners as substitute for sugar is necessary, especially for people engaged with obesity and diabetes. In spite of their useful effects in the adjustment of blood glucose level and reducing caloric intake, they may cause potential health risks, such as cancer and cardiovascular diseases. Therefore, it is important to investigate for natural and less harmful sweeteners, or even with useful side effects. Natural sweet proteins like Brazzein have been introduced as promising sweeteners with anticancer effects and reduced insulin requirements in diabetic patients. In the present study, the effect of both direct (static) and alternating (oscillating) electric fields (at 2.54 GHz frequency) with three intensities of 0.5, 0.8, and 1.0 V/nm on the stability of the Brazzein protein is studied using 60 ns molecular dynamics simulations with the GROMOS54A7 force field implemented in GROMACS. The analyzed quantities include root mean square displacements (RMSD), radius of gyration (Rg), root mean square fluctuations (RMSF), number of internal and external hydrogen bonds, solvent-accessible surface area (SASA), and the Ramachandran diagram. The results of these simulations indicated that the effect of the static electric field on RMSD and the number of hydrogen bonds is negligible, while oscillating electric field at intensities above 0.5 V/nm significantly increases RMSD and radius of gyration. These changes, together with the observed alteration in the secondary and tertiary structures of Brazzein, suggest that in the oscillating electric fields with intensities above 0.5 V/nm, the Brazzein protein undergoes denaturation. Both static and oscillating electric fields resulted in increased RMSF, particularly in the loop regions, and more pronounced in oscillating field. In the oscillating field, increasing field intensity leads to a decrease in the number of internal protein-protein hydrogen bonds and an increase in the external protein-water hydrogen bonds. Additionally, due to the unfolding of the second and third structures of the Brazzein protein in the oscillating electric field, the accessible surface area of the protein for the solvent is increased. Analysis of the Ramachandran diagram revealed that at higher field intensities, distribution of the points corresponding to the pair of Ramachandran angle values is increased in the forbidden regions. The results of the simulations at 330 K, compared with those obtained at 300 K, demonstrate that increasing temperature in the presence of weak oscillating electric field enhances the effects of the field, leading to elevated values in most indices, while at stronger electric fields, it has significantly diminished effects. The impact of temperature on the protein structure in the presence of static electric field is negligible.
