人體可以藉由各種精巧的機(jī)制控制蛋白表現(xiàn)的時(shí)間和表現(xiàn)量,，幾年前發(fā)現(xiàn)的核糖開(kāi)關(guān)(一些信使RNA內(nèi)的調(diào)控元素）就是其中一種。核糖開(kāi)關(guān)的功能好像按鈕般,，按下后可以阻止目標(biāo)蛋白的表現(xiàn),。
因此，如果能夠找到一種與病原體核糖開(kāi)關(guān)相結(jié)合的藥物,，就可以抑制細(xì)菌和真菌中重要蛋白的表現(xiàn),，因此核糖開(kāi)關(guān)有可能成為一種潛在的抗生素目標(biāo)。
最近,，波昂大學(xué)生命和醫(yī)學(xué)科學(xué)中心研究人員在核糖開(kāi)關(guān)的研究中又取得了重大突破,。由Michael Famulok率領(lǐng)的研究小組得到一種發(fā)夾狀RNA分子（hairpin-shaped RNA），可以區(qū)分核糖開(kāi)關(guān)的開(kāi)啟和關(guān)閉狀態(tài),。
為了表現(xiàn)目標(biāo)蛋白,，細(xì)胞必須先產(chǎn)生編碼蛋白的DNA和mRNA,，然后通過(guò)核糖體閱讀mRNA合成蛋白。有些蛋白在其含量充足的時(shí)候,，可以啟動(dòng)一種開(kāi)關(guān)來(lái)抑制自我合成,。這是因?yàn)閙RNA不僅包含編碼蛋白的遺傳物質(zhì)，而且包含具有調(diào)控功能的單元,。這種蛋白質(zhì)或其代謝產(chǎn)物可以與mRNA上的核糖開(kāi)關(guān)結(jié)合,，并改變核糖開(kāi)關(guān)的空間結(jié)構(gòu)，阻止核糖體繼續(xù)讀取編碼蛋白的mRNA片段,。
比如,，當(dāng)焦磷酸硫胺素（thiamine pyrophosphate，TPP）與大腸桿菌的thiM 核糖開(kāi)關(guān)結(jié)合后,，核糖體識(shí)別的mRNA片段（TPP的閱讀起點(diǎn)）被遮蔽了,。
Michael Famulok及其同事尋找一種可以區(qū)分核糖開(kāi)關(guān)開(kāi)啟和關(guān)閉狀態(tài)的探針。Aptamers（核酸適體）是已知的可以區(qū)分蛋白不同狀態(tài)的小 RNA,，與抗生素類似,，采用特異的空間結(jié)構(gòu)，選擇性地與目標(biāo)蛋白分子結(jié)合,。
研究人員選擇了兩種小的發(fā)夾型核酸適體,，能夠與處于開(kāi)啟狀態(tài)的核糖開(kāi)關(guān)牢固且專一地結(jié)合。結(jié)果顯示,，兩種核酸適體結(jié)合的區(qū)域不同：一種結(jié)合TPP的結(jié)合位置,，一種結(jié)合負(fù)責(zé)核糖開(kāi)關(guān)結(jié)構(gòu)轉(zhuǎn)變的區(qū)域。
Famulok等希望利用這些核酸適體來(lái)研究核糖開(kāi)關(guān)的功能,，希望可以研制出全新的抗菌劑,，用以阻斷細(xì)菌thiM 核糖開(kāi)關(guān)（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.
