A thermodynamic comparison of mesophilic and thermophilic ribonucleases H
A thermodynamic comparison of mesophilic and thermophilic ribonucleases H
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DOI：
10.1021/bi982684h
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发表时间：
1999-03-23
期刊：
影响因子：
2.9
通讯作者：
Marqusee, S
中科院分区：
文献类型：
--
作者：
Hollien, J;Marqusee, S
嗜热蛋白质提高热稳定性的机制尚不清楚，因为通常这些蛋白质的序列和结构与它们的中温同系物非常相似。为了深入了解热稳定性的基础，我们测定了两种核糖核酸酶H的蛋白质稳定性曲线，该曲线描述了两种核糖核酸酶H的展开自由能随温度的变化，其中一种来自嗜热大肠杆菌，另一种来自嗜热嗜热菌。圆二色谱信号被监测为温度和氯化胍浓度的函数，由此得到的展开自由能符合Gibbs-Helmholtz方程，得到了这些蛋白质的一组热力学参数。虽然这些蛋白质的最大稳定性发生在相似的温度下，但嗜热梭菌RNaseH的去折叠热容较低，导致去折叠自由能对温度的依赖性较小，从而导致较高的热熔化温度。此外，这些蛋白质在各自生物体的最佳生长温度下的稳定性相似，这表明热力学稳定性和灵活性之间的平衡对功能很重要。
The mechanisms by which thermophilic proteins attain their increased thermostability remain unclear, as usually the sequence and structure of these proteins are very similar to those of their mesophilic homologues. To gain insight into the basis of thermostability, we have determined protein stability curves describing the temperature dependence of the free energy of unfolding for two ribonucleases H, one from the mesophile Escherichia coli and one from the thermophile Thermus thermophilus. The circular dichroism signal was monitored as a function of temperature and guanidinium chloride concentration, and the resulting free energies of unfolding were fit to the Gibbs-Helmholtz equation to obtain a set of thermodynamic parameters for these proteins. Although the maximal stabilities for these proteins occur at similar temperatures, the heat capacity of unfolding for T. thermophilus RNase H is lower, resulting in a smaller temperature dependence of the free energy of unfolding and therefore a higher thermal melting temperature. In addition, the stabilities of these proteins are similar at the optimal growth temperatures for their respective organisms, suggesting that a balance of thermodynamic stability and flexibility is important for function.