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Conformational distributions at the N-peptide/boxB RNA interface studied using site-directed spin labeling

机译:使用定点旋转标记研究了N肽/ boxB RNA界面的构象分布

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摘要

In bacteriophage λ, interactions between a 22-amino acid peptide (called the N-peptide) and a stem–loop RNA element (called boxB) play a critical role in transcription anti-termination. The N-peptide/boxB complex has been extensively studied, and serves as a paradigm for understanding mechanisms of protein/RNA recognition. Particularly, ultrafast spectroscopy techniques have been applied to monitor picosecond fluorescence decay behaviors of 2-aminopurines embedded at various positions of the boxB RNA. The studies have led to a model in which the bound N-peptide exists in dynamic equilibrium between two states, with peptide C-terminal fragment either stacking on (i.e., the stacked state) or peeling away from (i.e., the unstacked state) the RNA loop. The function of the N-peptide/boxB complex seems to correlate with the fraction of the stacked state. Here, the N-peptide/boxB system is studied using the site-directed spin labeling technique, in which X-band electron paramagnetic resonance spectroscopy is applied to monitor nanosecond rotational behaviors of stable nitroxide radicals covalently attached to different positions of the N-peptide. The data reveal that in the nanosecond regime the C-terminal fragment of bound N-peptide adopts multiple discrete conformations within the complex. The characteristics of these conformations are consistent with the proposed stacked and unstacked states, and their distributions vary upon mutations within the N-peptide. These results suggest that the dynamic two-state model remains valid in the nanosecond regime, and represents a unique mode of function in the N-peptide/boxB RNA complex. It also demonstrates a connection between picosecond and nanosecond dynamics in a biological complex.
机译:在噬菌体λ中,22个氨基酸的肽(称为N肽)与茎环RNA元件(称为boxB)之间的相互作用在转录抗终止中起着至关重要的作用。 N-肽/ boxB复合物已被广泛研究,并作为理解蛋白质/ RNA识别机制的范例。特别是,超快光谱技术已应用于监测嵌入在boxB RNA各个位置的2-氨基嘌呤的皮秒荧光衰减行为。这些研究导致了一个模型,其中结合的N肽以两种状态之间的动态平衡存在,肽C末端片段要么堆叠在(即堆叠状态)上,要么从其剥离(即非堆叠状态)。 RNA环。 N肽/ boxB复合物的功能似乎与堆叠状态的分数相关。在这里,使用定点自旋标记技术研究N肽/ boxB系统,其中X波段电子顺磁共振光谱法用于监测共价附着在N肽不同位置的稳定氮氧自由基的纳秒旋转行为。 。数据显示,在纳秒范围内,结合的N肽的C末端片段在复合物中具有多个离散的构象。这些构象的特征与提议的堆叠和未堆叠状态一致,并且它们的分布随N肽内的突变而变化。这些结果表明动态的两个状态模型在纳秒范围内仍然有效,并且代表了N肽/ boxB RNA复合物中的独特功能模式。它还证明了生物复合物中皮秒和纳秒动力学之间的联系。

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