Auton Matthew, Ferreon Allan Chris M, Bolen D Wayne
The University of Texas Medical Branch, Department of Human Biological Chemistry and Genetics, 301 University Boulevard, 5.154 Medical Research Building, Galveston, TX 77555-1052, USA.
J Mol Biol. 2006 Sep 1;361(5):983-92. doi: 10.1016/j.jmb.2006.07.003. Epub 2006 Aug 4.
Osmolytes that are naturally selected to protect organisms against environmental stresses are known to confer stability to proteins via preferential exclusion from protein surfaces. Solvophobicity, surface tension, excluded volume, water structure changes and electrostatic repulsion are all examples of forces proposed to account for preferential exclusion and the ramifications exclusion has on protein properties. What has been lacking is a systematic way of determining which force(s) is(are) responsible for osmolyte effects. Here, we propose the use of two experimental metrics for assessing the abilities of various proposed forces to account for osmolyte-mediated effects on protein properties. Metric 1 requires prediction of the experimentally determined ability of the osmolyte to bring about folding/unfolding resulting from the application of the force in question (i.e. prediction of the m-value of the protein in osmolyte). Metric 2 requires prediction of the experimentally determined ability of the osmolyte to contract or expand the Stokes radius of the denatured state resulting from the application of the force. These metrics are applied to test separate claims that solvophobicity/solvophilicity and surface tension are driving forces for osmolyte-induced effects on protein stability. The results show clearly that solvophobic/solvophilic forces readily account for protein stability and denatured state dimensional effects, while surface tension alone fails to do so. The agreement between experimental and predicted m-values involves both positive and negative m-values for three different proteins, and as many as six different osmolytes, illustrating that the tests are robust and discriminating. The ability of the two metrics to distinguish which forces account for the effects of osmolytes on protein properties and which do not, provides a powerful means of investigating the origins of osmolyte-protein effects.
已知那些经过自然选择以保护生物体免受环境压力影响的渗透溶质，通过优先从蛋白质表面排除来赋予蛋白质稳定性。提出了疏溶剂性、表面张力、排除体积、水结构变化和静电排斥等各种力来解释优先排除以及排除对蛋白质性质的影响。一直缺乏的是一种系统的方法来确定哪种力（或哪些力）导致了渗透溶质效应。在此，我们提出使用两个实验指标来评估各种提出的力对渗透溶质介导的蛋白质性质影响的解释能力。指标1要求预测渗透溶质在施加相关力时导致折叠/去折叠的实验测定能力（即预测蛋白质在渗透溶质中的m值）。指标2要求预测渗透溶质在施加力时使变性态的斯托克斯半径收缩或扩张的实验测定能力。这些指标用于检验关于疏溶剂性/亲溶剂性和表面张力是渗透溶质诱导蛋白质稳定性变化驱动力的不同主张。结果清楚地表明，疏溶剂/亲溶剂力很容易解释蛋白质稳定性和变性态尺寸效应，而仅表面张力则无法做到。实验m值与预测m值之间的一致性涉及三种不同蛋白质以及多达六种不同渗透溶质的正m值和负m值，这表明这些测试是可靠且有区分力的。这两个指标区分哪些力导致渗透溶质对蛋白质性质的影响以及哪些力不导致这种影响的能力，为研究渗透溶质 - 蛋白质效应的起源提供了一种有力手段。
