美國(guó)伊利諾伊大學(xué)香檳分校生物化學(xué)系教授Raven H. Huang及其同事首次在細(xì)菌中發(fā)現(xiàn)了RNA修復(fù)系統(tǒng),。這是迄今為止發(fā)現(xiàn)的第二個(gè)RNA修復(fù)系統(tǒng),，第一個(gè)為噬菌體（可攻擊細(xì)菌的一種病毒）中的帶有2個(gè)蛋白的RNA修復(fù)系統(tǒng),。相關(guān)文章發(fā)表在本月的美國(guó)《科學(xué)》雜志以及《美國(guó)國(guó)家科學(xué)院院刊》上,。
此次發(fā)現(xiàn)的細(xì)菌RNA修復(fù)系統(tǒng)的新穎之處在于,，在受損的RNA封閉前,，一個(gè)甲基會(huì)附著在該RNA受損點(diǎn)的兩個(gè)主要羥基之上,，使得受損點(diǎn)無(wú)法繼續(xù)開(kāi)裂,，從而達(dá)到修復(fù)的效果,。這一發(fā)現(xiàn)對(duì)于保護(hù)細(xì)胞免遭核糖毒素的侵襲具有重要的意義。該毒素能使蛋白質(zhì)轉(zhuǎn)譯涉及的重要RNA發(fā)生開(kāi)裂,，從而導(dǎo)致細(xì)胞的死亡,。
由于新發(fā)現(xiàn)的RNA修復(fù)系統(tǒng)中對(duì)甲基負(fù)責(zé)的酶是細(xì)菌中的Hen1的同系物，因此該發(fā)現(xiàn)對(duì)理解RNA干涉以及動(dòng)物,、植物和其他真核生物的基因表達(dá)同樣具有相當(dāng)重要的意義,。
發(fā)表在《科學(xué)》雜志上的論文主要描述了RNA修復(fù)過(guò)程的全部機(jī)理，而發(fā)表在《美國(guó)國(guó)家科學(xué)院院刊》的論文則著重解析了甲基化反應(yīng)的化學(xué)機(jī)理,，尤其是細(xì)菌中的Hen1內(nèi)起主導(dǎo)作用的轉(zhuǎn)甲基酶的晶體結(jié)構(gòu),。由于真核態(tài)的Hen1能產(chǎn)生同樣的化學(xué)反應(yīng)，研究應(yīng)進(jìn)一步側(cè)重于理解真核生物中的RNA干涉,。
Huang表示,，Hen1是真核生物RNA干涉中產(chǎn)生小型非編碼RNA的三種基礎(chǔ)酶之一。雖然Hen1的同系物在細(xì)菌中確實(shí)存在,，但細(xì)菌內(nèi)卻沒(méi)有任何的RNA干涉,。因此，研究人員十分好奇,，想要破解細(xì)菌中的Hen1的具體功能,。黃雷文說(shuō)：“研究表明,，細(xì)菌中的Hen1與真核生物中的Hen1能產(chǎn)生同樣的化學(xué)反應(yīng)。但令我們感到驚訝的是,，雖然細(xì)菌中的Hen1并不在RNA干涉中發(fā)揮作用,，卻是RNA修復(fù)和修正系統(tǒng)中的一部分，它能使修復(fù)后的RNA恢復(fù)如新,，甚至能比全新的RNA發(fā)揮更好的功能,。”（生物谷Bioon.com）
生物谷推薦原始出處：
Science 9 October 2009:DOI: 10.1126/science.1179480
Reconstituting Bacterial RNA Repair and Modification in Vitro
Chio Mui Chan,1,* Chun Zhou,1,* Raven H. Huang1,2,
Ribotoxins kill cells by endonucleotically cleaving essential RNAs involved in protein translation. We report here that a stable heterotetramer composed of two bacterial proteins, Pnkp and Hen1, was able to repair transfer RNAs cleaved by ribotoxins in vitro. Before the broken RNAs were ligated by the heterotetramer, a methyl group was added to the 2'-OH group that participated in the original RNA cut. Because of the methylation, RNAs repaired by bacterial Pnkp/Hen1 heterotetramer could not be cleaved again by the ribotoxins. Thus, unlike eukaryotic Hen1 involved in RNA interference, the bacterial Hen1 is part of an RNA repair and modification system.
1 Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
2 Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
PNAS October 12, 2009, doi: 10.1073/pnas.0907540106
Structural and biochemical insights into 2′-O-methylation at the 3′-terminal nucleotide of RNA by Hen1
Chio Mui Chana,1, Chun Zhoua,1, Joseph S. Brunzelleb and Raven H. Huanga,c,2
aDepartment of Biochemistry and
cCenter for Biophysics and Computational Biology, University of Illinois at Urbana–Champaign, Urbana, IL 61801; and
bLife Science Collaborative Access Team, Argonne National Laboratory, Argonne, IL 60439
Small RNAs of ≈20–30 nt have diverse and important biological roles in eukaryotic organisms. After being generated by Dicer or Piwi proteins, all small RNAs in plants and a subset of small RNAs in animals are further modified at their 3′-terminal nucleotides via 2′-O-methylation, carried out by the S-adenosylmethionine-dependent methyltransferase (MTase) Hen1. Methylation at the 3′ terminus is vital for biological functions of these small RNAs. Here, we report four crystal structures of the MTase domain of a bacterial homolog of Hen1 from Clostridium thermocellum and Anabaena variabilis, which are enzymatically indistinguishable from the eukaryotic Hen1 in their ability to methylate small single-stranded RNAs. The structures reveal that, in addition to the core fold of the MTase domain shared by other RNA and DNA MTases, the MTase domain of Hen1 possesses a motif and a domain that are highly conserved and are unique to Hen1. The unique motif and domain are likely to be involved in RNA substrate recognition and catalysis. The structures allowed us to construct a docking model of an RNA substrate bound to the MTase domain of bacterial Hen1, which is likely similar to that of the eukaryotic counterpart. The model, supported by mutational studies, provides insight into RNA substrate specificity and catalytic mechanism of Hen1.
