Yokoyama Kazushige, Ichiki Akane
Department of Chemistry, The State University of New York Geneseo College, 1 College Cir., Geneseo, NY 14454, USA.
Colloid Interface Sci Commun. 2021 Jan;40:100356. doi: 10.1016/j.colcom.2020.100356. Epub 2020 Dec 26.
The affinity of the SARS-CoV-2 spike protein (S protein) to gold nano-particles was examined through spectral shifts of SPR (Surface Plasmon Resonance) band. Gold nano-colloidal particles are sensitive to the conformational change of the protein adsorbed over the particles' surface. As the pH value was gradually lowered from approximately neutral pH to an acidic pH ( pH 2), all mixtures of S protein with the gold colloids ≥30 nm in diameter exhibited a drastic red-shift of the average SPR band peak at one pH value more than that observed for bare gold colloids. The surface coverage fraction (Θ) of S protein over the nano-particle's surface was extracted and all showed relatively small coverage values ( Θ ~ 0.30). The SPR band peak shift was also examined as the pH values were hopped between pH ~ 3 and pH ~ 10 (pH hopping). As the pH values hopped, an alternation of the average SPR band peaks were observed. A significant amplitude of an alternation was especially observed for the mixture of S protein with gold ≥30 nm of gold size implying the reproduction of pH induced reversible protein folding. We hypothesize that the pH hopping scheme captured a reversible transition between folded or Down conformation (pH ≥ ~7) and unfolded or Up (pH ~ 3) conformation of RBD (receptor binding domain). The acidic condition may also dimerize the S protein through RBD. The Up conformation or dimerization of S protein are considered to be connected to the other gold nano particles forming gold nano-particle aggregates.
通过表面等离子体共振（SPR）带的光谱位移，研究了严重急性呼吸综合征冠状病毒2（SARS-CoV-2）刺突蛋白（S蛋白）与金纳米颗粒的亲和力。金纳米胶体颗粒对吸附在颗粒表面的蛋白质的构象变化敏感。随着pH值从大约中性pH逐渐降低到酸性pH（pH 2），直径≥30 nm的S蛋白与金胶体的所有混合物在一个pH值下均表现出平均SPR带峰的急剧红移，比裸金胶体观察到的红移更大。提取了纳米颗粒表面S蛋白的表面覆盖分数（Θ），所有结果均显示相对较小的覆盖值（Θ ~ 0.30）。还在pH值在3和10之间跳跃（pH跳跃）时检查了SPR带峰位移。随着pH值跳跃，观察到平均SPR带峰的交替变化。对于S蛋白与金尺寸≥30 nm的金的混合物，特别观察到显著的交替幅度，这意味着pH诱导的可逆蛋白质折叠的再现。我们假设pH跳跃方案捕捉到了受体结合域（RBD）在折叠或向下构象（pH ≥ ~7）与未折叠或向上（pH ~ 3）构象之间的可逆转变。酸性条件也可能通过RBD使S蛋白二聚化。S蛋白的向上构象或二聚化被认为与形成金纳米颗粒聚集体的其他金纳米颗粒有关。
