Department of Biochemistry, University of Missouri, Columbia, MO, USA.
EMBO Rep. 2014 Feb;15(2):185-90. doi: 10.1002/embr.201337762. Epub 2014 Jan 8.
During protein synthesis, mRNA and tRNA are moved through the ribosome by the process of translocation. The small diameter of the mRNA entrance tunnel only permits unstructured mRNA to pass through. However, there are structured elements within mRNA that present a barrier for translocation that must be unwound. The ribosome has been shown to unwind RNA in the absence of additional factors, but the mechanism remains unclear. Here, we show using single molecule Förster resonance energy transfer and small angle X-ray scattering experiments a new global conformational state of the ribosome. In the presence of the frameshift inducing dnaX hairpin, the ribosomal subunits are driven into a hyper-rotated state and the L1 stalk is predominantly in an open conformation. This previously unobserved conformational state provides structural insight into the helicase activity of the ribosome and may have important implications for understanding the mechanism of reading frame maintenance.
在蛋白质合成过程中,mRNA 和 tRNA 通过移位过程穿过核糖体。mRNA 入口隧道的小直径仅允许无结构的 mRNA 通过。然而,mRNA 内存在结构元件,这些元件构成了移位的障碍,必须解开。已经表明核糖体可以在没有其他因素的情况下解开 RNA,但机制尚不清楚。在这里,我们使用单分子Förster 共振能量转移和小角度 X 射线散射实验显示了核糖体的一种新的整体构象状态。在诱导移码的 dnaX 发夹存在的情况下,核糖体亚基被驱动进入超旋转状态,并且 L1 茎主要处于开放构象。这种以前未观察到的构象状态为核糖体的解旋酶活性提供了结构上的见解,并且可能对理解阅读框维持的机制具有重要意义。