Haemagglutinin of influenza virus expressed from a cloned gene promotes membrane fusion
Haemagglutinin of influenza virus expressed from a cloned gene promotes membrane fusion
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克隆基因表达的流感病毒血凝素促进膜融合
作者：
Judy White;A. Helenius;M. Gething
有包膜的动物病毒通过涉及病毒膜与细胞膜融合的过程进入并感染细胞。在某些情况下（例如仙台病毒1），融合事件发生在质膜上;对于包括流感在内的许多其他病毒，通过胞内囊泡（如内体或溶酶体）的膜进入，其中融合由内源性低pH触发2 -6。这种pH依赖性融合活性已在体外研究，使用培养细胞7 -9、红细胞9，10和脂质体11 -13作为靶。融合是病毒表面糖蛋白的一种功能12，并在每种病毒种属和毒株特有的阈值pH下发生8。在流感病毒的情况下，有强有力的证据表明，血凝素糖蛋白在病毒感染性和融合活性中具有关键作用9，12，14-16。这两个过程都需要血凝素前体HA 0翻译后蛋白水解裂解为活性形式的分子HA，HA由两个二硫键键合的亚基HA 1和HA 217，18组成。在HA 2亚基上产生新的N-末端，其C-末端嵌入病毒膜中19。在融合所需的低pH值下，切割的HA经历构象变化，暴露出HA 220的先前隐藏的疏水性N-末端，可能使其能够与靶膜相互作用。虽然已经确定HA是融合所必需的，但尚不清楚单独的HA是否足够，或者是否涉及其他病毒蛋白21。在这里，我们使用从插入重组猿猴病毒40（SV 40）载体22的HA基因的克隆拷贝表达HA的细胞来证明HA分子在没有任何其他流感病毒编码组分的情况下显示融合。这些结果开启了使用HA介导的膜融合作为将外源分子递送到哺乳动物细胞中的系统的可能性。
Enveloped animal viruses enter and infect cells by a process involving fusion of the viral membrane with a cellular membrane. In some cases (for example, Sendai virus1), the fusion event occurs at the plasma membrane; for many other viruses including influenza, entry occurs through the membranes of intracellular vesicles such as endosomes or lysosomes, where the fusion is triggered by the endogenous lowpH2–6. ThispH-dependent fusion activity has been studiedin vitrousing as targets cultured cells7–9, erythrocytes9,10and liposomes11–13. Fusion is a function of the viral surface glycoproteins12and occurs at a thresholdpH that is characteristic of each virus species and strain8. In the case of influenza virus, there is strong evidence that the haemagglutinin glycoprotein has a key role in both virus infectivity and fusion activity9,12,14–16. Both processes require a post-translational proteolytic cleavage of the haemagglutinin precursor, HA0, into the active form of the molecule, HA, which consists of two disulphide-bonded subunits, HA1 and HA217,18. A new N-terminus is generated on the HA2 subunit, the C-terminus of which is embedded in the virus membrane19. At the lowpH values required for fusion the cleaved HA undergoes a conformational change exposing this previously buried hydrophobic N-terminus of HA220, possibly enabling it to interact with the target membrane. While it has been established that HA is necessary for fusion, it is unclear whether HA alone is sufficient or whether other viral proteins are involved21. Here we use cells expressing HA from a cloned copy of the HA gene inserted into a recombinant simian virus 40 (SV40) vector22to demonstrate that the HA molecule displays fusion in the absence of any other influenza virus-encoded components. These results open the possibility of using HA-mediated membrane fusion as a system to deliver foreign molecules into mammalian cells.