Abstract：
The btuB riboswitch is a regulatory RNA sequence controlling gene expression of the outer membrane B12 transport protein BtuB by specifically binding coenzyme B12 (AdoCbl) as its natural ligand. The B12 sensing riboswitch class is known to accept various B12 derivatives, leading to a division into two riboswitch subclasses, dependent on the size of the apical ligand. Here we focus on the role of side chains b and e on affinity and proper recognition, i. e. correct structural switch of the btuB RNA, which belongs to the AdoCbl-binding class I. Chemical modification of these side chains disturbs crucial hydrogen bonds and/or electrostatic interactions with the RNA, its effect on both affinity and switching being monitored by in-line probing. Chemical modifications at sidechain b of vitamin B12 show larger effects indicating crucial B12-RNA interactions. When introducing the same modification to AdoCbl the influence of any side-chain modification tested is reduced. This renders the impact of the adenosyl-ligand for B12-btuB riboswitch recognition clearly beyond the known role in affinity.
摘要：
btuB核糖开关是通过特异性结合辅酶B12(AdoCbl)作为其天然配体来控制外膜B12转运蛋白BtuB的基因表达的调节性RNA序列。已知B12传感核糖开关类接受各种B12衍生物，导致分成两个核糖开关子类，取决于顶端配体的大小。在这里，我们关注侧链b和e在亲和力和正确识别方面的作用，即btuBRNA的正确结构转换，属于AdoCbl结合类I。这些侧链的化学修饰会干扰关键的氢键和/或与RNA的静电相互作用，它对亲和力和开关的影响被在线探测监控。维生素B12侧链b的化学修饰显示出更大的作用，表明关键的B12-RNA相互作用。当向AdoCbl引入相同的修饰时,所测试的任何侧链修饰的影响降低。这使得腺苷-配体对B12-btuB核糖开关识别的影响明显超出了已知的亲和力作用。
