SARS
冠狀病毒核鞘蛋白之雙聚合區域之結晶結構分析與其包裹病毒RNA
之機制探討Structure of the SARS Coronavirus Nucleocapsid protein Dimerization Domain: Implications for Helical Packaging of Viral
RNA
嚴重急性呼吸道症候群（ Severe Acute Respiratory Syndrome, SARS ） 爆發於西元 2002 年底，是一種有潛力造成全球風險的傳染性疾病。 造 成嚴重急性呼吸道症候群的致病原為一新品種的冠狀病毒（ Coronaviru s ）。核鞘蛋白（ Nucleocapsid ）是是 SARS 冠狀病毒中最主要的結構 蛋白，具有兩個功能區域： N 端的 RNA 結合區域（ RNA-binding do main, RBD ）以及 C 端的雙聚合區域（ Dimerization domain, DD ），兩 功能區域間以一無結構的片段連結。根據本論文的實驗結果，雙聚合區 域可與單股的 RNA 以及 DNA 結合，且其結合的親和力強過原本所定 義的 RNA 結合區域。在本論文中，我們也解出了雙聚合區域的結晶結 構，其解析度可到 2.5 ? 。此雙聚合體區域的結晶結構，在每一個晶體 的非對稱單元中含有四個雙聚體（ dimer ），四個雙聚體可環繞成一個 八聚體（ octamer ）的中空環狀結構。從晶體排列的角度來看，接連排 列的八聚體可形成一個左手旋的雙股螺旋結構，此雙股螺旋結構具有兩 個平行且帶正電的凹槽環繞於其上，為可能的 RNA 纏繞位置。根據我 們解出的結構，可進一步的瞭解核鞘蛋白如何快速且有效的包裹病毒 R NA 的機制。更可讓我們對冠狀病毒的 ribonucleoprotein 的構性有更深 入的認識。
Severe acute respiratory syndrome (SARS) emerged at the end of 2002 that is a potential world wide risk. The causative agent of SARS has been attrib uted to a novel coronavirus (SARS-CoV). The nucleocapsid protein of SA RS coronavirus is a major structual protein that contains two structural do mains: the N-terminal putative RNA-binding domain (RBD) and the C-ter minal dimerization domain (DD), flanked by disordered regions. Here we r eport that the DD binds to single-stranded RNA and DNA, with stronger af finities than those of the putative RBD. We have determined the crystal str ucture of the DD to 2.5 ? resolution. In the crystal, the DD of nucleocapsid protein exists as dimers. Four dimer molecules form a ring-like octameric s tructure with a central cavity in an asymmetric unit. Packaging of the octa mers in the crystal created two parallel, positively-charge grooves that win d around the octamer as a left-handed double-stranded helix and suggests a novel mechanism for fast and efficient helical viral RNA packaging. The st ructure thus formed conforms to known features of coronavirus ribonucleo proteins.
