2009年8月5日，北京生命科學(xué)研究所葉克窮實(shí)驗(yàn)室在《美國(guó)科學(xué)院院報(bào)》在線發(fā)表題為“Structural organization of box C/D RNA-guided RNA methyltransferase”的文章,，該研究解析了C/D RNA蛋白質(zhì)復(fù)合物的晶體結(jié)構(gòu),，促進(jìn)了對(duì)該復(fù)合物的組合方式和其修飾RNA甲基化機(jī)理的了解,。
RNA分子不僅僅作為編碼蛋白質(zhì)的模板,，許多不編碼蛋白質(zhì)的RNA在生命活動(dòng)也有重要的功能,。C/D RNA就是一類廣泛存在于古細(xì)菌和真核生物中的非編碼RNA,，他們因?yàn)楹泄餐谋Ｊ匦蛄心KC和D而得名,。C/D RNA主要功能是指導(dǎo)RNA底物——如rRNA,、snRNA和tRNA——發(fā)生特定位點(diǎn)上核糖的甲基化。C/D RNA含有一段向?qū)蛄?，這段序列通過(guò)和修飾位點(diǎn)兩邊的堿基序列互補(bǔ)配對(duì)而實(shí)現(xiàn)對(duì)底物的特異性選擇,。在古細(xì)菌中,，C/D RNA與RNA結(jié)合蛋白L7Ae、骨架蛋白Nop5和甲基化酶fibrillarin三個(gè)蛋白質(zhì)亞基組成RNA-蛋白質(zhì)復(fù)合體,，該復(fù)合物能對(duì)底物進(jìn)行特異位點(diǎn)的甲基化修飾,。雖然科學(xué)家對(duì)該復(fù)合體的組裝和功能研究已經(jīng)持續(xù)了十多年時(shí)間，但目前還不了解復(fù)合物的整體結(jié)構(gòu),。該研究通過(guò)結(jié)構(gòu)生物學(xué)手段,，使用X射線衍射技術(shù)解析了一個(gè)4埃分辨率的C/D RNP復(fù)合物晶體結(jié)構(gòu)。該結(jié)構(gòu)包含了全部三個(gè)蛋白亞基和半個(gè)C/D RNA,，也是目前獲得的最完整的C/D RNP復(fù)合物結(jié)構(gòu),。該結(jié)構(gòu)加深了對(duì)復(fù)合物組裝方式的認(rèn)識(shí)，發(fā)現(xiàn)C/D RNA是通過(guò)和L7Ae和Nop5的碳端結(jié)構(gòu)域共同結(jié)合裝配到復(fù)合物,，進(jìn)一步證實(shí)催化亞基fibrillarin和Nop5氮端結(jié)構(gòu)域結(jié)合,。作者發(fā)現(xiàn)不同結(jié)構(gòu)中催化亞基占據(jù)了不同的位置，顯示了該復(fù)合物結(jié)構(gòu)內(nèi)部的活動(dòng)性,，并推測(cè)催化亞基的運(yùn)動(dòng)可能是其結(jié)合底物過(guò)程中的必要步驟,。另外結(jié)構(gòu)提示Nop5碳端結(jié)構(gòu)域上的一個(gè)結(jié)構(gòu)突起可能影響C/D RNA的特異裝配，以及C/D RNA和底物的結(jié)合,。新的結(jié)構(gòu)模型促進(jìn)了對(duì)C/D RNP的組合方式和工作機(jī)理更深入的理解,。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS August 5, 2009, doi: 10.1073/pnas.0905128106
Structural organization of box C/D RNA-guided RNA methyltransferase
Keqiong Yea,1, Ru Jiaa, Jinzhong Lina, Minghua Jua, Jin Penga, Anbi Xua and Liman Zhanga,b
aNational Institute of Biological Sciences, Beijing 102206, China; and
bGraduate Program at Chinese Academy of Medical Sciences and Peking union Medical College, Beijing 100730, China
Box C/D guide RNAs are abundant noncoding RNAs that primarily function to direct the 2′-O-methylation of specific nucleotides by base-pairing with substrate RNAs. In archaea, a bipartite C/D RNA assembles with L7Ae, Nop5, and the methyltransferase fibrillarin into a modification enzyme with unique substrate specificity. Here, we determined the crystal structure of an archaeal C/D RNA–protein complex (RNP) composed of all 3 core proteins and an engineered half-guide RNA at 4 ? resolution, as well as 2 protein substructures at higher resolution. The RNP structure reveals that the C-terminal domains of Nop5 in the dimeric complex provide symmetric anchoring sites for 2 L7Ae-associated kink-turn motifs of the C/D RNA. A prominent protrusion in Nop5 seems to be important for guide RNA organization and function and for discriminating the structurally related U4 snRNA. Multiple conformations of the N-terminal domain of Nop5 and its associated fibrillarin in different structures indicate the inherent flexibility of the catalytic module, suggesting that a swinging motion of the catalytic module is part of the enzyme mechanism. We also built a model of a native C/D RNP with substrate and fibrillarin in an active conformation. Our results provide insight into the overall organization and mechanism of action of C/D RNA–guided RNA methyltransferases.
