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首页> 外文期刊>Journal of Molecular Biology >Protein-dependent transition states for ribonucleoprotein assembly
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Protein-dependent transition states for ribonucleoprotein assembly

机译：核糖核蛋白组装的蛋白质依赖性过渡态

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Native folding and splicing by the Saccharomyces cerevisiae mitochondrial bI5 group I intron RNA is facilitated by both the S. cerevisiae CBP2 and Neurospora crassa CYT-18 protein cofactors. Both protein-bI5 RNA complexes splice at similar rates, suggesting that the RNA active site structure is similar in both ribonucleoproteins. In contrast, the two proteins assemble with the bI5 RNA by distinct mechanisms and bind opposing, but partially overlapping, sides of the group I intron catalytic core. Assembly with CBP2 is limited by a slow, unimolecular RNA folding step characterized by a negligible activation enthalpy. We show that assembly with CYT-18 shows four distinctive features. (1) CYT-18 binds stably to the bI5 RNA at the diffusion controlled limit, but assembly to a catalytically active RNA structure is still limited by RNA folding, as visualized directly using time-resolved footprinting. (2) This mechanism of rapid stable protein binding followed by subsequent assembly steps has a distinctive kinetic signature: the apparent ratio of k(off) to k(on), determined in a partitioning experiment, differs from the equilibrium K-d by a large factor. (3) Assembly with CYT-18 is characterized by a large activation enthalpy, consistent with a rate limiting conformational rearrangement. (4) Because assembly from the kinetically trapped state is faster at elevated temperature, we can identify conditions where CYT-18 accelerates (catalyzes) bI5 RNA folding relative to assembly with CBP2. (C) 2001 Academic Press. [References: 50]
机译：啤酒糖酵母线粒体bI5组I内含子RNA的天然折叠和剪接受啤酒糖酵母CBP2和神经孢霉CYT-18蛋白辅因子的促进。两种蛋白质-bI5 RNA复合物的接合速率相似，表明两种核糖核蛋白中的RNA活性位点结构相似。相反，这两种蛋白通过不同的机制与bI5 RNA组装在一起，并结合I组内含子催化核心相对但部分重叠的侧面。与CBP2的组装受到缓慢的单分子RNA折叠步骤的限制，该步骤的特征在于活化焓可忽略不计。我们显示，与CYT-18的组装显示出四个鲜明的特征。 （1）CYT-18在扩散控制的极限上稳定地与bI5 RNA结合，但是组装成催化活性RNA的结构仍然受到RNA折叠的限制，如使用时间分辨足迹直接观察到的那样。 （2）这种快速稳定的蛋白质结合以及随后的组装步骤的机制具有独特的动力学特征：在分配实验中确定的k（off）与k（on）的表观比例与平衡Kd的差异很大。 。 （3）与CYT-18组装的特征在于大的活化焓，与速率限制的构象重排一致。 （4）由于在高温下从动力学受阻态组装的速度更快，因此我们可以确定CYT-18相对于用CBP2组装加速（催化）bI5 RNA折叠的条件。 （C）2001学术出版社。 [参考：50]

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