Reiss Caroline W, Strobel Scott A
Department of Molecular Biophysics and Biochemistry, Chemical Biology Institute, Yale University, West Haven, Connecticut 06516, USA.
RNA. 2017 Sep;23(9):1338-1343. doi: 10.1261/rna.061804.117. Epub 2017 Jun 9.
The guanidine-II riboswitch, also known as , is a conserved mRNA element with more than 800 examples in bacteria. It consists of two stem-loops capped by identical, conserved tetraloops that are separated by a linker region of variable length and sequence. Like the guanidine-I riboswitch, it controls the expression of guanidine carboxylases and SugE-like genes. The guanidine-II riboswitch specifically binds free guanidinium cations and functions as a translationally controlled on-switch. Here we report the structure of a P2 stem-loop from the guanidine-II riboswitch aptamer bound to guanidine at 1.57 Å resolution. The hairpins dimerize via the conserved tetraloop, which also contains the binding pocket. Two guanidinium molecules bind near the dimerization interface, one in each tetraloop. The guanidinium cation is engaged in extensive hydrogen bonding to the RNA. Contacts include the Hoogsteen face of a guanine base and three nonbridging phosphate oxygens. Cation-π interactions and ionic interactions also stabilize ligand binding. The guanidine-II riboswitch utilizes the same recognition strategies as the guanidine-I riboswitch while adopting an entirely different and much smaller RNA fold.
胍-II核糖开关，也称为 ，是一种保守的mRNA元件，在细菌中有800多个实例。它由两个茎环组成，茎环由相同的保守四环封顶，两个四环由长度和序列可变的连接区隔开。与胍-I核糖开关一样，它控制胍羧化酶和SugE样基因的表达。胍-II核糖开关特异性结合游离胍阳离子，并作为翻译控制的开启开关发挥作用。在这里，我们报告了来自胍-II核糖开关适体的P2茎环与胍结合的结构，分辨率为1.57 Å。发夹通过保守的四环二聚化，该四环也包含结合口袋。两个胍分子在二聚化界面附近结合，每个四环中各有一个。胍阳离子与RNA形成广泛的氢键。相互作用包括鸟嘌呤碱基的Hoogsteen面和三个非桥连磷酸氧。阳离子-π相互作用和离子相互作用也稳定配体结合。胍-II核糖开关采用与胍-I核糖开关相同的识别策略，同时采用完全不同且小得多的RNA折叠结构。
