Riboswitches are structural elements found in mRNA molecules that couple small-molecule binding to regulation of gene expression, usually by controlling transcription or translation. We have determined high-resolution crystal structures of theykkCguanidine III riboswitch fromThermobifida fusca. The riboswitch forms a classic H-type pseudoknot that includes a triple helix that is continuous with a central core of conserved nucleotides. These form a left-handed helical ramp of inter-nucleotide interactions, generating the guanidinium cation binding site. The ligand is hydrogen bonded to the Hoogsteen edges of two guanine bases. The binding pocket has a side opening that can accommodate a small side chain, shown by structures with bound methylguanidine, aminoguanidine, ethylguanidine, and agmatine. Comparison of the new structure with those of the guanidine I and II riboswitches reveals that evolution generated three different structural solutions for guanidine binding and subsequent gene regulation, although with some common elements.

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胍 III 核糖开关的结构

核糖开关是在 mRNA 分子中发现的结构元件，它们将小分子结合与基因表达的调节结合起来，通常通过控制转录或翻译。我们已经确定了来自Thermobifida fusca的ykkC胍III核糖开关的高分辨率晶体结构。核糖开关形成一个经典的 H 型假结，包括与保守核苷酸的中心核心连续的三螺旋。这些形成核苷酸间相互作用的左旋螺旋斜坡，产生胍阳离子结合位点。配体与两个鸟嘌呤碱基的 Hoogsteen 边缘氢键合。结合口袋有一个侧开口，可以容纳一条小的侧链，如结合甲基胍、氨基胍、乙基胍和胍丁胺的结构所示​​。