Structure, Stability, and Folding of Ribonuclease H1 from the Moderately Thermophilic Chlorobium tepidum: Comparison with Thermophilic and Mesophilic Homologues
Structure, Stability, and Folding of Ribonuclease H1 from the Moderately Thermophilic Chlorobium tepidum: Comparison with Thermophilic and Mesophilic Homologues
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DOI：
10.1021/bi900305p
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发表时间：
2009-06-30
期刊：
影响因子：
2.9
通讯作者：
Marqusee, Susan
中科院分区：
文献类型：
--
作者：
Ratcliff, Kathleen;Corn, Jacob;Marqusee, Susan
来自嗜热生物的蛋白质能够在使典型的中温蛋白质不活跃的条件下发挥作用。对同源的中温和嗜热蛋白质进行成对比较，可以帮助确定导致这种热稳定性的蛋白质能量格局的能量特征。以前对嗜热嗜热菌和嗜中性菌的细菌核糖核酸酶H(RNase H)的研究表明，热稳定性的部分原因是嗜热蛋白在展开时热容的异常低变化(Delta C-p)[Hollien，J.，and Marqusee，S.(1999)BioChemical 38,3831-3836]。在这里，我们进一步研究了几乎相同的蛋白质如何通过向先前描述的中温和嗜热对添加适度的嗜热同系物来适应不同的热限制。我们从氯杆菌中鉴定出一个可能的核糖核酸酶H。Tepium.证明它是一种具有活性的RNase H，并采用RNase H折叠.中等嗜热蛋白质的熔化温度(T-m)与中温同系物相似，但也像嗜热同系物一样，具有令人惊讶的低增量C-p。这一新的RNaseH通过与先前研究的RNasesH相似的途径折叠。这些结果表明，降低Delta C-p可能是实现某些蛋白质家族嗜热性的一般策略，并暗示折叠核心是这一效应的主要贡献者。现在应该有可能设计出显示所需的嗜热或中温性质的核糖核酸酶H，如它们的增量C-p值所定义的那样，从而以可预测的方式微调能量格局。
Proteins from thermophilic organisms are able to function under conditions that render a typical mesophilic protein inactive. Pairwise comparisons of homologous mesophilic and thermophilic proteins can help to identify the energetic features of a protein's energy landscape that lead to such thermostability. Previous studies of bacterial ribonucleases H (RNases H) from the thermophile Thermus thermophilus and the mesophile Escherichia coli revealed that the thermostability arises In part from an unusually low change in heat capacity upon unfolding (Delta C-p) for the thermophilic protein [Hollien, J., and Marqusee, S. (1999) Biochemistry 38, 3831-3836]. Here, we have further examined how nearly identical proteins can adapt to different thermal constraints by adding a moderately thermophilic homologue to the previously characterized mesophilic and thermophilic pair. We identified a putative RNase H from Chlorobium. tepidum and demonstrated that it is an active RNase H and adopts the RNase H fold. The moderately thermophilic protein has a melting temperature (T-m) similar to that of the mesophilic homologue yet also has a surprisingly low Delta C-p, like the thermophilic homologue. This new RNase H folds through a pathway similar to that of the previously studied RNases H. These results suggest that lowering the Delta C-p may be a general strategy for achieving thermophilicity for some protein families and implicate the folding core as the major contributor to this effect. It should now be possible to design RNases H that display the desired thermophilic or mesophilic properties, as defined by their Delta C-p values, and therefore fine-tune the energy landscape in a predictable fashion.