克沙奇B3型病毒3C蛋白酶及其抑制劑複合體結構分析--抗病毒藥物設計之應用

Abstract

克沙奇B3型病毒屬於腸病毒的一種，主要感染孩童造成急性或慢性心肌炎，其伴隨的病症嚴重者會導致死亡，目前除了減輕病痛及減緩病症的治療外，並沒有針對克沙奇B3型病毒的專用藥物。克沙奇病毒的3C蛋白酶屬於微小RNA病毒(picornaviridae) Cysteine蛋白酶，專門負責切割病毒轉譯的複合蛋白質，使產生各具功能的多種蛋白質，由於此3C蛋白酶在克沙奇型病毒的成熟及感染過程中不可或缺，以及它在不同克沙奇病毒株的高度一致性，使得3C蛋白酶成為抗病毒藥物發展的主要目標。在此,我們解出第一個克沙奇B3型病毒3C蛋白酶和它C147A突變株的晶體結構，且解析度分別達到1.8 Å 及1.4 Å；根據結構分析，克沙奇B3型病毒3C蛋白酶具有類似chymotrypsin的摺疊方式， 且其催化中心Cys-His-Glu與大部份Serine蛋白酶的催化中心Ser-His-Asp有著相似的構造。進一步，我們利用多種SARS類3C蛋白酶的抑制劑，分析它們對克沙奇B3型病毒3C蛋白酶的抑制能力，並且解出其中一個抑制劑與蛋白酶共結晶的結構，解析度為1.7 Å；抑制劑 TG4998 和克沙奇B3型病毒3C蛋白酶之間，透過與催化中心Cys147形成共價鍵，以及與活化區內其他氨基酸形成氫鍵而結合，在這些作用中，TG4998對於抑制效果的影響，主要透過其P1、P2及P4位置與克沙奇B3型病毒3C蛋白酶的作用。綜合我們觀察克沙奇B3型病毒3C蛋白酶所做的結構分析，可為抗病毒藥物提供設計與改良上的重要依據。

Coxsackievirus B3 (CVB3) causes acute or chronic myocarditis, which may lead to death, especially in children. Until now, there is no specific therapy for CVB3 other than treatment to relieve pain and other symptoms. CVB3 3C protease (3Cpro), a member of the picornaviridae cysteine protease, is required to cleave the viral polyprotein into functional proteins. CVB3 3Cpro is highly conserved in different strains and essential for viral maturation and infectivity, making it an attractive target for the development of antiviral drugs. Here we report the first crystal structures of native CVB3 3Cpro and its mutant (C147A) at 1.8 Å and 1.4 Å resolution, espectively. The structure of CVB3 3Cpro adopts a chymotrypsin-like fold and possesses a catalytic triad, Cys-His-Glu, which is similar to the configuration of the Ser-His-Asp triad in almost all serine proteases. Furthermore, we analyzed the inhibition activity of CVB3 3Cpro with several SARS 3C-like protease inhibitors and determined a structure of co-crystallized proteaseinhibitor complex at 1.7 Å resolution. The inhibitor, TG4998, interacts with CVB3 3Cpro through a covalent bond with Cys147 of the catalytic triad and hydrogen bonds in the active-site pocket. The main effect on enzyme-inhibition depends upon the interactions between CVB3 3Cpro and the P1, P2 and P4 residues of TG4998. Collectively, these structural characteristics provide valuable basis for antiviral drug design.