Corver J, Bron R, Snippe H, Kraaijeveld C, Wilschut J
Department of Physiological Chemistry, GUIDE, University of Groningen, The Netherlands.
Virology. 1997 Nov 10;238(1):14-21. doi: 10.1006/viro.1997.8799.
Semliki Forest virus (SFV) has been shown previously to fuse efficiently with cholesterol- and sphingolipid-containing liposomal model membranes in a low-pH-dependent manner. Several steps can be distinguished in this process, including low-pH-induced irreversible binding of the virus to the liposomes, facilitated by target membrane cholesterol, and subsequent fusion of the viral membrane with the liposomal bilayer, specifically catalyzed by target membrane sphingolipid. Binding and fusion are mediated by the heterodimeric viral envelope glycoprotein E2/E1. At low pH the heterodimer dissociates, and the E1 monomers convert to a homotrimeric structure, the presumed fusion-active conformation of the viral spike. In this paper, we demonstrate that SFV-liposome fusion is specifically inhibited by Zn2+ ions. The inhibition is at the level of the fusion reaction itself, since virus-liposome binding was found to be unaffected. Zn2+ did not inhibit E2/E1 dissociation, but severely inhibited exposure of an acid-specific epitope on E1, E1 homotrimer formation, and acquisition of trypsin-resistance. It is concluded that virus--liposome binding solely requires low-pH-induced E2/E1 heterodimer dissociation, while fusion depends on further rearrangements in the E1 spike protein. As these rearrangements occur subsequent to the binding step, their precise course, including the formation of a fusion complex, may be influenced by interaction of E1 with target membrane lipids.
先前已证明，辛德毕斯病毒（SFV）能以低pH依赖的方式与含胆固醇和鞘脂的脂质体模型膜高效融合。此过程可区分出几个步骤，包括低pH诱导病毒与脂质体不可逆结合，这一过程由靶膜胆固醇促进，随后病毒膜与脂质体双层融合，具体由靶膜鞘脂催化。结合和融合由异二聚体病毒包膜糖蛋白E2/E1介导。在低pH条件下，异二聚体解离，E1单体转变为同三聚体结构，这是病毒刺突推测的融合活性构象。在本文中，我们证明Zn2+离子可特异性抑制SFV与脂质体的融合。这种抑制作用发生在融合反应本身的水平，因为发现病毒与脂质体的结合不受影响。Zn2+不抑制E2/E1解离，但严重抑制E1上酸特异性表位的暴露、E1同三聚体的形成以及胰蛋白酶抗性的获得。得出的结论是，病毒与脂质体的结合仅需要低pH诱导的E2/E1异二聚体解离，而融合则取决于E1刺突蛋白的进一步重排。由于这些重排在结合步骤之后发生，其精确过程，包括融合复合物的形成，可能会受到E1与靶膜脂质相互作用的影响。
