PAC:PB1N复合体的三维结构。其中“龙嘴”部位的紫色飘带为PB1 N端多肽，“龙头”为PA_C亚基； 背景为禽流感病毒的电镜负染图片及病毒颗粒剖面示意图。
近年来，由H5N1亚型禽流感病毒引起的疫情广泛传播对人类的健康造成全球性的重大威胁。由于病毒的不断变异，开发新型抗流感药物成为各国极为迫切的重大课题。其中，揭示与流感病毒密切相关的蛋白质的三维结构不仅对揭示流感病毒复制机制具有重要科学意义，而且对开发抗流感病毒药物具有重要价值。最近，由中科院生物物理研究所刘迎芳研究员领导的研究组和饶子和院士领导的研究小组在这一领域取得突破性进展，他们在国际上率先揭示了流感病毒聚合酶关键部分PA亚基与PB1多肽复合体的精细三维结构。
流感A病毒聚合酶由三种蛋白组成——PA、PB1和PB2，是转录和复制的关键。现在，两个小组报告了禽流感病毒H5N1 PA 的C-端区域在与PB1的PA结合区域所形成的复合物中的晶体结构。这项结构研究对于新型抗病毒药物的设计可能会有用
流感病毒基因组含有8个RNA片段，已知可以编码11种病毒蛋白质。其中，由PA,PB1和PB23个亚基组成的聚合酶复合体是负责病毒基因组RNA复制以及病毒mRNA转录的关键组分，同时由于它的高度保守性、低突变率，成为抗流感病毒药物设计的重要靶点。多年来的研究认为，PB1是病毒RNA聚合酶的催化亚基，负责病毒RNA的复制以及转录；PB2是负责以一种称为“Snatch”的方式夺取宿主mRNA的CAP帽子结构用于病毒mRNA转录。而PA亚基不但参与病毒复制过程，而且还参与病毒RNA转录、内切核酸酶活性、具有蛋白酶活性以及参与病毒粒子组装等多种病毒活动过程，因而在整个聚合酶复合体的研究中显得格外重要。在经过晶体生长条件筛选、晶体质量优化、高分辨率数据收集、相位解析、电子密度图解释以及结构修正等难关，他们利用全新的思路，解析了PA与PB1氨基端多肽蛋白复合体的2.9埃分辨率晶体结构。该结构清晰显示了PA与PB1多肽相互作用模式，发现该作用位点的氨基酸残基在流感病毒中高度保守，这为广谱抗流感(包括人流感和禽流感)药物研究提供了一个理想的靶蛋白。同时，根据该复合体结构以及已知的一些蛋白突变体研究结果，推测了PA亚基在聚合酶中作用，为进一步功能研究提供了分子基础。这一复合体结构的揭示，对揭示流感病毒聚合酶作用机制以及开展针对流感病毒药物设计工作都具有十分重要意义。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 454, 1123-1126 (28 August 2008) | doi:10.1038/nature07120
Crystal structure of the polymerase PAC–PB1N complex from an avian influenza H5N1 virus
Xiaojing He1, Jie Zhou1, Mark Bartlam2, Rongguang Zhang3, Jianyuan Ma1, Zhiyong Lou4, Xuemei Li1,4, Jingjing Li1, Andrzej Joachimiak3, Zonghao Zeng1, Ruowen Ge5, Zihe Rao1,2,4 & Yingfang Liu1
National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
College of Life Sciences and Tianjin State Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
Midwest Center for Structural Genomics and Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Laboratory of Structural Biology, Tsinghua University, Beijing 100084, China
Department of Biological Sciences, National University of Singapore, 117543 Singapore
Correspondence to: Zihe Rao1,2,4Yingfang Liu1 Correspondence and requests for materials should be addressed to Z.R. (Email: raozh@xtal.tsinghua.edu.cn) or Y.L. (Email: liuy@ibp.ac.cn).
The recent emergence of highly pathogenic avian influenza A virus strains with subtype H5N1 pose a global threat to human health1. Elucidation of the underlying mechanisms of viral replication is critical for development of anti-influenza virus drugs2. The influenza RNA-dependent RNA polymerase (RdRp) heterotrimer has crucial roles in viral RNA replication and transcription. It contains three proteins: PA, PB1 and PB2. PB1 harbours polymerase and endonuclease activities and PB2 is responsible for cap binding3, 4; PA is implicated in RNA replication5, 6, 7, 8, 9, 10 and proteolytic activity11, 12, 13, 14, although its function is less clearly defined. Here we report the 2.9 ångström structure of avian H5N1 influenza A virus PA (PAC, residues 257–716) in complex with the PA-binding region of PB1 (PB1N, residues 1–25). PAC has a fold resembling a dragon's head with PB1N clamped into its open 'jaws'. PB1N is a known inhibitor that blocks assembly of the polymerase heterotrimer and abolishes viral replication. Our structure provides details for the binding of PB1N to PAC at the atomic level, demonstrating a potential target for novel anti-influenza therapeutics. We also discuss a potential nucleotide binding site and the roles of some known residues involved in polymerase activity. Furthermore, to explore the role of PA in viral replication and transcription, we propose a model for the influenza RdRp heterotrimer by comparing PAC with the 3 reovirus polymerase structure, and docking the PAC structure into an available low resolution electron microscopy map.
