Turn‐on aptamers are in vitro‐selected RNAs that bind to conditionally fluorescent small molecules and enhance their fluorescence. Upon binding TO1‐biotin, the iMango‐III aptamer achieves the largest fluorescence enhancement reported for turn‐on aptamers (over 5000‐fold). This aptamer was generated by structure‐guided engineering and functional reselection of the parental aptamer Mango‐III. Structures of both Mango‐III and iMango‐III have previously been determined by conventional cryocrystallography using synchrotron X‐radiation. Using an X‐ray free‐electron laser (XFEL), the room‐temperature iMango‐III–TO1‐biotin co‐crystal structure has now been determined at 3.0 Å resolution. This structural model, which was refined against a data set of ∼1300 diffraction images (each from a single crystal), is largely consistent with the structures determined from single‐crystal data sets collected at 100 K. This constitutes a technical benchmark on the way to XFEL pump–probe experiments on fluorescent RNA–small molecule complexes.

中文翻译：

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使用X射线自由电子激光的iMango-III荧光RNA适体的共晶体结构。

开启适体是体外选择的RNA，可与有条件的荧光小分子结合并增强其荧光。结合TO1-生物素后，i Mango-III适体获得了报道的开启适体的最大荧光增强作用（超过5000倍）。该适体是通过结构指导的工程学和亲本适体Mango-III的功能重选而生成的。Mango-III和i Mango-III的结构以前都是使用同步加速器X射线通过常规的低温晶体学确定的。使用X射线自由电子激光（XFEL），室温i现已确定了芒果III–TO1-生物素共晶体的结构，分辨率为3.0Å。该结构模型针对约1300个衍射图像（每个来自单晶）的数据集进行了细化，在很大程度上与从100 K收集的单晶数据集确定的结构一致。这构成了该方法的技术基准XFEL泵–荧光RNA –小分子复合物的探针实验。