Connell Katelyn B, Miller Erik J, Marqusee Susan
Chemical Biology Graduate Group, Department of Chemistry, Institute for Quantitative Biosciences-Berkeley, University of California, Berkeley, CA 94720-3220, USA.
J Mol Biol. 2009 Aug 14;391(2):450-60. doi: 10.1016/j.jmb.2009.05.085. Epub 2009 Jun 6.
Proteins can sample a variety of partially folded conformations during the transition between the unfolded and native states. Some proteins never significantly populate these high-energy states and fold by an apparently two-state process. However, many proteins populate detectable, partially folded forms during the folding process. The role of such intermediates is a matter of considerable debate. A single amino acid change can convert Escherichia coli ribonuclease H from a three-state folder that populates a kinetic intermediate to one that folds in an apparent two-state fashion. We have compared the folding trajectories of the three-state RNase H and the two-state RNase H, proteins with the same native-state topology but altered regional stability, using a protein engineering approach. Our data suggest that both versions of RNase H fold through a similar trajectory with similar high-energy conformations. Mutations in the core and the periphery of the protein affect similar aspects of folding for both variants, suggesting a common trajectory with folding of the core region followed by the folding of the periphery. Our results suggest that formation of specific partially folded conformations may be a general feature of protein folding that can promote, rather than hinder, efficient folding.
在从未折叠状态转变为天然状态的过程中，蛋白质能够呈现出多种部分折叠的构象。一些蛋白质从未显著占据这些高能状态，而是通过明显的两态过程进行折叠。然而，许多蛋白质在折叠过程中会形成可检测到的部分折叠形式。这些中间体的作用存在相当大的争议。单个氨基酸的改变可将大肠杆菌核糖核酸酶H从一种会形成动力学中间体的三态折叠蛋白转变为以明显两态方式折叠的蛋白。我们采用蛋白质工程方法，比较了具有相同天然状态拓扑结构但区域稳定性不同的三态核糖核酸酶H和两态核糖核酸酶H的折叠轨迹。我们的数据表明，两种形式的核糖核酸酶H都通过相似的轨迹折叠，具有相似的高能构象。蛋白质核心区域和外围区域的突变对两种变体折叠的相似方面产生影响，这表明存在一条共同的轨迹，即先折叠核心区域，随后折叠外围区域。我们的结果表明，特定部分折叠构象的形成可能是蛋白质折叠的一个普遍特征，它能够促进而非阻碍高效折叠。
