Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
Int J Biol Macromol. 2019 Feb 15;123:409-419. doi: 10.1016/j.ijbiomac.2018.11.120. Epub 2018 Nov 14.
Fibrillation of proteins is a major cause of various neurodegenerative diseases and its exact mechanism of formation is yet unclear instead of extensive research. However, the role of metal ions influencing fibrillation of proteins is gaining more attention recently. Herein, we have investigated the role of various concentrations of the transition metal, Zn(II), on the fibrillation of Bovine Serum Albumin (BSA) at the physiological pH 7.4. Several biophysical and simulation techniques were employed in order to analyze the same. Thioflavin T intensity and residual protein investigations revealed that fibrillation of BSA was significantly decelerated and accelerated at 1:3 and 1:4 ratios of BSA-Zn(II), respectively; while it was found to be independent at other ratios (1:1 and 1:2). Fourier transform infrared spectroscopy analysis revealed that the transition of BSA from α-helical conformation to the β-sheet rich structure is greatly resisted at 1:3 ratio, however, the same is promoted at 1:4 ratio. Similarly, dynamic light scattering and field emission transmission electron microscopy analyses further confirmed the above observations. Furthermore, Isothermal Titration Calorimetry revealed the interaction of Zn(II) towards four binding sites of BSA with preferential affinities. Molecular dynamics studies predicted that at 1:3 ratio, the C- and N-terminal zones of BSA were least flexible owing to more stable conformation. Moreover, the solvent accessible surface area and structural analyses showed increase in hydrophilicity and more conserved secondary structure, respectively at 1:3 ratio. We propose that BSA fibrillation is indeed dependent on particular Zn(II) concentration, the temperature of the microenvironment of BSA, the number of binding sites exposed due to unfolding and the conformation after metal binding.
蛋白质的纤维化是各种神经退行性疾病的主要原因，其确切的形成机制尚不清楚，尽管已经进行了广泛的研究。然而，最近人们越来越关注金属离子对蛋白质纤维化的影响。在此，我们研究了各种浓度的过渡金属锌离子（Zn(II)）在生理 pH 值 7.4 下对牛血清白蛋白（BSA）纤维化的影响。采用了几种生物物理和模拟技术来分析这一现象。噻唑蓝 T 强度和残留蛋白研究表明，BSA-Zn(II) 摩尔比为 1:3 和 1:4 时，BSA 的纤维化分别显著减缓和加速；而在其他比例（1:1 和 1:2）下则独立。傅里叶变换红外光谱分析表明，BSA 从α-螺旋构象向富含β-折叠结构的转变在 1:3 比例下受到很大阻碍，但在 1:4 比例下则得到促进。同样，动态光散射和场发射透射电子显微镜分析进一步证实了上述观察结果。此外，等温滴定量热法揭示了 Zn(II)与 BSA 的四个结合位点的相互作用，具有优先亲和力。分子动力学研究预测，在 1:3 比例下，BSA 的 C 端和 N 端区域由于更稳定的构象而具有最小的灵活性。此外，溶剂可及表面积和结构分析分别表明在 1:3 比例下亲水性增加和二级结构更保守。我们提出，BSA 的纤维化确实取决于特定的 Zn(II)浓度、BSA 微环境的温度、由于展开而暴露的结合位点数量以及金属结合后的构象。
