2012年1月10日,，PNAS在線發(fā)表了中國(guó)科學(xué)院生物物理研究所朱平研究組程凌鵬副研究員等人的研究論文“Atomic model of a cypovirus built from cryo-EM structure provides insight into the mechanism of mRNA capping”,。該研究利用生物成像技術(shù)實(shí)驗(yàn)室2010年4月調(diào)試成功的冷凍電鏡平臺(tái)，用單顆粒圖像處理技術(shù)獲得了呼腸孤病毒科的質(zhì)型多角體病毒近原子分辨率的三維結(jié)構(gòu)（3.9埃）,，并獨(dú)立構(gòu)建了全原子模型,。對(duì)研究dsRNA病毒的mRNA加帽機(jī)制有重要意義。（詳見(jiàn)PNAS：呼腸孤病毒科的質(zhì)型多角體病毒近原子分辨率的三維結(jié)構(gòu)）
近日,，程凌鵬等人利用之前的研究,，深入研究了質(zhì)型多角體病毒在轉(zhuǎn)錄過(guò)程中的結(jié)構(gòu),，于4月6日再次在PNAS在線發(fā)表了一篇名為“Cryo-EM structure of a transcribing cypovirus”的論文。
已知呼腸病毒科家族中的雙鏈RNA病毒能夠轉(zhuǎn)錄及加帽初期mRNA,。有趣的是,，整個(gè)的轉(zhuǎn)錄周期，二十面體病毒的衣殼一直保持完整,，但是mRNA轉(zhuǎn)錄及加帽過(guò)程是被病毒衣殼蛋白協(xié)調(diào)的機(jī)制還未可知,。質(zhì)型多角體病毒屬則提供了一個(gè)好的模式系統(tǒng)，來(lái)研究呼腸病毒科家族的mRNA轉(zhuǎn)錄及加帽機(jī)制,。
研究人員通過(guò)冷凍電子顯微鏡技術(shù)得到的一個(gè)近乎原子分辨率的密度圖,，得到了一個(gè)轉(zhuǎn)錄中的質(zhì)型多角體病毒的完整主干模型。對(duì)比于非轉(zhuǎn)錄中的質(zhì)型多角體病毒屬的結(jié)構(gòu),，轉(zhuǎn)錄中的質(zhì)型多角體病毒的主要衣殼蛋白經(jīng)歷了一系列的構(gòu)象改變,，這導(dǎo)致了衣殼的結(jié)構(gòu)改變：一方面是增大的衣殼腔，在緊密包裝的衣殼中,，這對(duì)基因組RNA提供了更多的移靈活性,；另一方面是衣殼內(nèi)擴(kuò)大的peripentonal通道,，研究表明這是初期mRNA的通道,。
除此以外，在每一個(gè)五倍軸turret蛋白的構(gòu)象改變導(dǎo)致了一個(gè)相對(duì)開(kāi)放的turret,。研究還發(fā)現(xiàn),，在mRNA加帽期間，一個(gè)被轉(zhuǎn)移到5'端去磷酸化mRNA的GMP,，被發(fā)現(xiàn)在turret蛋白口袋樣結(jié)構(gòu)的尿苷轉(zhuǎn)移酶結(jié)構(gòu)域,。（生物谷Deepblue編譯）
doi: 10.1073/pnas.1200206109
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Cryo-EM structure of a transcribing cypovirus
Chongwen Yanga, Gang Jia, Hongrong Liub, Kai Zhanga, Guangqiao Liua, Fei Suna, Ping Zhua, and Lingpeng Chenga.
Double-stranded RNA viruses in the family Reoviridae are capable of transcribing and capping nascent mRNA within an icosahedral viral capsid that remains intact throughout repeated transcription cycles.However, how the highly coordinated mRNA transcription and capping process is facilitated by viral capsid proteins is still unknown. Cypovirus provides a good model system for studying the mRNA transcription and capping mechanism of viruses in the family Reoviridae.Here, we report a full backbone model of a transcribing cypovirus built from a near-atomic-resolution density map by cryoelectron microscopy.Compared with the structure of a nontranscribing cypovirus, the major capsid proteins of transcribing cypovirus undergo a series of conformational changes, giving rise to structural changes in the capsid shell: (i) an enlarged capsid chamber, which provides genomic RNA with more flexibility to move within the densely packed capsid, and (ii) a widened peripentonal channel in the capsid shell, which we confirmed to be a pathway for nascent mRNA.A rod-like structure attributable to a partially resolved nascent mRNA was observed in this channel.In addition, conformational change in the turret protein results in a relatively open turret at each fivefold axis.A GMP moiety, which is transferred to 5’-diphosphorylated mRNA during the mRNA capping reaction, was identified in the pocket-like guanylyltransferase domain of the turret protein.
