Reiss Caroline W, Xiong Yong, Strobel Scott A
Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT 06511, USA; Chemical Biology Institute, Yale University, West Haven, CT 06516, USA.
Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT 06511, USA.
Structure. 2017 Jan 3;25(1):195-202. doi: 10.1016/j.str.2016.11.020. Epub 2016 Dec 22.
The guanidine-I riboswitch is a conserved RNA element with approximately 2,000 known examples across four phyla of bacteria. It exists upstream of nitrogen metabolism and multidrug resistance transporter genes and alters expression through the specific recognition of a free guanidinium cation. Here we report the structure of a guanidine riboswitch aptamer from Sulfobacillus acidophilus at 2.7 Å resolution. Helices P1, P1a, P1b, and P2 form a coaxial stack that acts as a scaffold for ligand binding. A previously unidentified P3 helix docks into P1a to form the guanidinium binding pocket, which is completely enclosed. Every functional group of the ligand is recognized through hydrogen bonding to guanine bases and phosphate oxygens. Guanidinium binding is further stabilized through cation-π interactions with guanine bases. This allows the riboswitch to recognize guanidinium while excluding other bacterial metabolites with a guanidino group, including the amino acid arginine.
胍-I核糖开关是一种保守的RNA元件，在四个细菌门类中已知约有2000个实例。它存在于氮代谢和多药耐药转运蛋白基因的上游，并通过对游离胍阳离子的特异性识别来改变表达。在此，我们报道了嗜酸硫杆菌胍核糖开关适体在2.7 Å分辨率下的结构。螺旋P1、P1a、P1b和P2形成一个同轴堆叠，作为配体结合的支架。一个先前未鉴定的P3螺旋对接至P1a以形成完全封闭的胍结合口袋。配体的每个官能团通过与鸟嘌呤碱基和磷酸氧的氢键相互作用被识别。胍的结合通过与鸟嘌呤碱基的阳离子-π相互作用进一步稳定。这使得核糖开关能够识别胍，同时排除其他带有胍基的细菌代谢物，包括氨基酸精氨酸。
