Volume changes of proteins adsorbed on silica particles
Volume changes of proteins adsorbed on silica particles
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DOI：
10.1039/c2sm25961c
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发表时间：
2012-01-01
期刊：
影响因子：
3.4
通讯作者：
Czeslik, Claus
中科院分区：
文献类型：
--
作者：
Koo, Juny;Czeslik, Claus
蛋白质通常停留在界面上，在那里它们的构象和生物活性可以被改变。在这项研究中，我们以葡萄球菌核酸酶（SNase）为模型蛋白，胶体二氧化硅颗粒为模型吸附剂，研究蛋白质折叠稳定性和分子体积的潜在变化。利用SNase的本征色氨酸荧光，在1-2500 bar范围内进行了高压荧光实验，测定了其折叠稳定性和分子体积。在pH = 7.0和25℃时，SNase溶解在散装溶液中，其特征是展开的体积变化为-73 mL mol（-1）。当SNase被吸附在二氧化硅颗粒上时，该值急剧降低。在这里，体积变化在41至32 mL mol（-1）的范围内，可以测量不同表面电荷密度的二氧化硅颗粒。此外，标准吉布斯能变化和展开压力在SNase的吸附状态下显著降低，表明表面诱导的蛋白质天然结构的不稳定。并对ph值的影响进行了研究。而在7-10范围内的ph变化对溶解SNase的压力驱动展开没有显著影响，对吸附的SNase有很强的ph依赖性。当pH接近SNase的等电点时，吸附蛋白的构象稳定性急剧降低。本研究结果揭示了蛋白质吸附过程中构象变化的新观点。结果表明，SNase的分子体积是由大约两个水分子所对应的蛋白质空隙体积的部分填充而降低的。
Proteins often stay at interfaces, where their conformation and biological activity can be altered. In this study, we investigate the underlying changes in the folding stability and molecular volume of proteins using staphylococcal nuclease (SNase) as the model protein and colloidal silica particles as the model adsorbent. The folding stability and molecular volume have been determined by high-pressure fluorescence experiments in the range of 1-2500 bar utilizing the intrinsic Trp fluorescence of SNase. At pH = 7.0 and 25 degrees C, SNase, dissolved in bulk solution, is characterized by a volume change of unfolding of -73 mL mol(-1). This value is drastically reduced, when SNase is adsorbed on silica particles. Here, volume changes in the range of 41 to 32 mL mol(-1) can be measured at silica particles differing in their surface charge density. In addition, the standard Gibbs energy change and the pressure of unfolding are strongly reduced in the adsorbed state of SNase indicating a surface-induced destabilization of the protein native structure. The effect of the pH-value has been studied as well. Whereas a pH-change in the range of 7-10 has no significant effect on the pressure-driven unfolding of dissolved SNase, strong pH-dependence is observed for the adsorbed SNase. As the pH is approaching the isoelectric point of SNase, the conformational stability of the adsorbed protein is lowered drastically. The results of this study reveal a novel view on conformational changes upon protein adsorption. It is suggested that the molecular volume of SNase is lowered by a partial filling of the protein void volume corresponding to about two water molecules.