Sidorova N Y, Rau D C
Laboratory of Structural Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 1996 Oct 29;93(22):12272-7. doi: 10.1073/pnas.93.22.12272.
The free energy difference between complexes of the restriction nuclease EcoRI with nonspecific DNA and with the enzyme's recognition sequence is linearly dependent on the water chemical potential of the solution, set using several very different solutes, ranging from glycine and glycerol to triethylene glycol and sucrose. This osmotic dependence indicates that the nonspecific complex sequesters some 110 waters more than the specific complex with the recognition sequence. The insensitivity of the difference in number of waters released to the solute identity further indicates that this water is sequestered in a space that is sterically inaccessible to solutes, most likely at the protein-DNA interface of the nonspecific complex. Calculations based on the structure of the specific complex suggest that the apposing DNA and protein surfaces in the nonspecific complex retain approximately a full hydration layer of water.
限制性核酸内切酶EcoRI与非特异性DNA形成的复合物以及与该酶识别序列形成的复合物之间的自由能差，与溶液的水化学势呈线性相关，溶液的水化学势通过使用几种非常不同的溶质来设定，这些溶质包括甘氨酸、甘油、三甘醇和蔗糖。这种渗透压依赖性表明，非特异性复合物比与识别序列形成的特异性复合物多隔离约110个水分子。释放的水分子数量差异对溶质特性不敏感，这进一步表明这些水分子被隔离在一个溶质无法进入的空间中，很可能位于非特异性复合物的蛋白质-DNA界面处。基于特异性复合物结构的计算表明，非特异性复合物中相对的DNA和蛋白质表面保留了大约一整个水化层的水。
