人体可以藉由各种精巧的机制控制蛋白表现的时间和表现量，几年前发现的核糖开关(一些信使RNA内的调控元素）就是其中一种。核糖开关的功能好像按钮般，按下后可以阻止目标蛋白的表现。
因此，如果能够找到一种与病原体核糖开关相结合的药物，就可以抑制细菌和真菌中重要蛋白的表现，因此核糖开关有可能成为一种潜在的抗生素目标。
最近，波昂大学生命和医学科学中心研究人员在核糖开关的研究中又取得了重大突破。由Michael Famulok率领的研究小组得到一种发夹状RNA分子（hairpin-shaped RNA），可以区分核糖开关的开启和关闭状态。
为了表现目标蛋白，细胞必须先产生编码蛋白的DNA和mRNA，然后通过核糖体阅读mRNA合成蛋白。有些蛋白在其含量充足的时候，可以启动一种开关来抑制自我合成。这是因为mRNA不仅包含编码蛋白的遗传物质，而且包含具有调控功能的单元。这种蛋白质或其代谢产物可以与mRNA上的核糖开关结合，并改变核糖开关的空间结构，阻止核糖体继续读取编码蛋白的mRNA片段。
比如，当焦磷酸硫胺素（thiamine pyrophosphate，TPP）与大肠杆菌的thiM 核糖开关结合后，核糖体识别的mRNA片段（TPP的阅读起点）被遮蔽了。
Michael Famulok及其同事寻找一种可以区分核糖开关开启和关闭状态的探针。Aptamers（核酸适体）是已知的可以区分蛋白不同状态的小 RNA，与抗生素类似，采用特异的空间结构，选择性地与目标蛋白分子结合。
研究人员选择了两种小的发夹型核酸适体，能够与处于开启状态的核糖开关牢固且专一地结合。结果显示，两种核酸适体结合的区域不同：一种结合TPP的结合位置，一种结合负责核糖开关结构转变的区域。
Famulok等希望利用这些核酸适体来研究核糖开关的功能，希望可以研制出全新的抗菌剂，用以阻断细菌thiM 核糖开关（如TPP）。
英文原文：
Hairpins for Switches: Artificial RNA ligands differentiate between on and off states of riboswitches
How does an organism know when it must produce a protein and in what amount? Clever control mechanisms are responsible for the regulation of protein biosynthesis. One such type of mechanism, discovered only a few years ago, is riboswitches, which function as a sort of “off” switch for the production of certain proteins. These could be a useful point of attack for novel antibiotics if it were possible to find drugs that bind to the switches of pathogens and “turn off” the biosynthesis of essential proteins in bacteria or fungi.
A team at the interdisciplinary Life and Medical Sciences Center at the University of Bonn has now taken a meaningful step toward a better understanding of riboswitches. Researchers led by Michael Famulok have successfully produced hairpin-shaped RNA molecules that are able to differentiate between riboswitches in the on and off states.
In order to produce a specific protein, a cell first generates a copy of the corresponding gene of the DNA. This blueprint containing the construction plans for the protein is called messenger RNA (mRNA). By using its ribosomes, the cell then reads the mRNA code and synthesizes the protein. Some proteins can activate a “switch” to halt their own synthesis once they are present in sufficient quantity. This is because the mRNA does not only contain the genetic code for the protein but can also contain segments with a switching function.
The protein or a closely connected metabolite binds to this riboswitch and changes its spatial structure such that the mRNA segments controlling the protein production can no longer be read off. For example, when the metabolite thiamine pyrophosphate (TPP) binds to the thiM riboswitch of E. coli bacteria, an mRNA segment recognized by the ribosome as the starting point for “reading” the plan is covered up.
Michael Famulok and his team searched for a probe that can differentiate between off and on. Aptamers are known for their ability to differentiate between different states of proteins. Aptamers are short RNA strands that adopt a specific spatial structure and, like antibodies, selectively bind to specific target molecules. So, why not riboswitches? Over several steps starting from a “library”, a randomly generated large number of highly varied RNA sequences, the scientists selected two short hairpin-shaped aptamers that bind very strongly and specifically to the riboswitch in the “on” position. It turned out that the two hairpins bind to different locations: one to the TPP binding site and the other to a domain responsible for the change in structure of the riboswitch. Both hairpins are crowded when TPP molecules move the riboswitch to the “off” conformation.
Famulok and his team hope to use these aptamers to gain new insights into the function of riboswitches. This could help in the search for a completely new class of antimicrobial agents that block the bacterial thiM riboswitch just like TPP.
