Wilschut J, Corver J, Nieva J L, Bron R, Moesby L, Reddy K C, Bittman R
Department of Physiological Chemistry, Groningen Institute for Drug Studies, University of Groningen, The Netherlands.
Mol Membr Biol. 1995 Jan-Mar;12(1):143-9. doi: 10.3109/09687689509038510.
Semliki Forest virus (SFV) utilizes a membrane fusion strategy to introduce its genome into the host cell. After binding to cell-surface receptors, virus particles are internalized through receptor-mediated endocytosis and directed to the endosomal cell compartment. Subsequently, triggered by the acid pH in the lumen of the endosomes, the viral envelope fuses with the endosomal membrane. As a result of this fusion reaction the viral RNA gains access to the cell cytosol. Low-pH-induced fusion of SFV, in model systems as well as in cells, has been demonstrated previously to be strictly dependent on the presence of cholesterol in the target membrane. In this paper, we show that fusion of SFV with cholesterol-containing liposomes depends on sphingomyelin (SM) or other sphingolipids in the target membrane, ceramide representing the sphingolipid minimally required for mediating the process. The action of the sphingolipid is confined to the actual fusion event, cholesterol being necessary and sufficient for low-pH-dependent binding of the virus to target membranes. The 3-hydroxyl group on the sphingosine backbone plays a key role in the SFV fusion reaction, since 3-deoxy-sphingomyelin does not support the process. This, and the remarkably low levels of sphingolipid required for half-maximal fusion (1-2 mol%), suggest that the sphingolipid does not play a structural role in SFV fusion, but rather acts as a cofactor, possibly through activation of the viral fusion protein. Domain formation between cholesterol and sphingolipid, although it may facilitate SFV fusion, is unlikely to play a crucial role in the process.
塞姆利基森林病毒（SFV）采用膜融合策略将其基因组导入宿主细胞。病毒颗粒与细胞表面受体结合后，通过受体介导的内吞作用内化，并被导向内体细胞区室。随后，在内体腔的酸性pH值触发下，病毒包膜与内体膜融合。这种融合反应的结果是病毒RNA进入细胞质溶胶。先前已证明，在模型系统以及细胞中，低pH诱导的SFV融合严格依赖于靶膜中胆固醇的存在。在本文中，我们表明SFV与含胆固醇脂质体的融合取决于靶膜中的鞘磷脂（SM）或其他鞘脂，神经酰胺是介导该过程所需的最低限度的鞘脂。鞘脂的作用仅限于实际的融合事件，胆固醇对于病毒与靶膜的低pH依赖性结合是必要且充分的。鞘氨醇主链上的3-羟基在SFV融合反应中起关键作用，因为3-脱氧鞘磷脂不支持该过程。这一点，以及半最大融合所需的极低水平的鞘脂（1-2摩尔%）表明，鞘脂在SFV融合中不发挥结构作用，而是作为一种辅助因子，可能通过激活病毒融合蛋白发挥作用。胆固醇和鞘脂之间的结构域形成，虽然可能促进SFV融合，但在该过程中不太可能起关键作用。
