Magnesium controls aptamer-expression platform switching in the SAM-I riboswitch.
Magnesium controls aptamer-expression platform switching in the SAM-I riboswitch.
复制标题
镁控制 SAM-I 核糖开关中适体表达平台的切换。
DOI：
10.1093/nar/gky1311
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发表时间：
2019
影响因子：
14.9
通讯作者：
Sanbonmatsu,KarissaY
中科院分区：
文献类型：
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作者：
Roy,Susmita;Hennelly,ScottP;Lammert,Heiko;Onuchic,JoséN;Sanbonmatsu,KarissaY
大多数核糖开关的研究仍然局限于配体结合适体结构域。然而，在核糖开关介导的转录调控过程中，适体结构域和表达平台竞争共享链。如果表达平台占主导地位，则形成抗终止子螺旋，并且转录过程是活跃的（ON状态）。当适体占主导地位时，转录终止（OFF状态）。在这里，我们使用表达平台切换实验测定和基于结构的静电模拟来研究全长SAM-1核糖开关的这种ON-OFF转变及其镁浓度依赖性。有趣的是，我们发现随着镁浓度的增加，关闭种群与打开种群的比率非单调变化。在添加镁后，适体结构域预组织，填充OFF状态，但仅达到中间镁浓度水平。较高的镁浓度优先稳定抗终止子螺旋，填充ON状态，相对不稳定OFF状态。镁介导的适体表达平台结构域闭合解释了在较高镁浓度下OFF状态的这种相对不稳定。我们的研究揭示了镁在控制其下游基因转录方面的功能潜力，并强调了生理镁浓度范围附近的窄浓度范围的重要性，在细菌基因调控的OFF和ON状态之间取得平衡。
Investigations of most riboswitches remain confined to the ligand-binding aptamer domain. However, during the riboswitch mediated transcription regulation process, the aptamer domain and the expression platform compete for a shared strand. If the expression platform dominates, an anti-terminator helix is formed, and the transcription process is active (ON state). When the aptamer dominates, transcription is terminated (OFF state). Here, we use an expression platform switching experimental assay and structure-based electrostatic simulations to investigate this ON-OFF transition of the full length SAM-I riboswitch and its magnesium concentration dependence. Interestingly, we find the ratio of the OFF population to the ON population to vary non-monotonically as magnesium concentration increases. Upon addition of magnesium, the aptamer domain pre-organizes, populating the OFF state, but only up to an intermediate magnesium concentration level. Higher magnesium concentration preferentially stabilizes the anti-terminator helix, populating the ON state, relatively destabilizing the OFF state. Magnesium mediated aptamer-expression platform domain closure explains this relative destabilization of the OFF state at higher magnesium concentration. Our study reveals the functional potential of magnesium in controlling transcription of its downstream genes and underscores the importance of a narrow concentration regime near the physiological magnesium concentration ranges, striking a balance between the OFF and ON states in bacterial gene regulation.