Yang D, Hwang D, Qiu Z, Gillam S
Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
J Virol. 1998 Nov;72(11):8747-55. doi: 10.1128/JVI.72.11.8747-8755.1998.
Rubella virus (RV) virions contain two glycosylated membrane proteins, E1 and E2, that exist as a heterodimer and form the viral spike complexes on the virion surface. Formation of an E1-E2 heterodimer is required for transport of E1 out of the endoplasmic reticulum lumen to the Golgi apparatus and plasma membrane. To investigate the nature of the E1-E2 interaction, we have introduced mutations in the internal hydrophobic region (residues 81 to 109) of E1. Substitution of serine at Cys82 (mutant C82S) or deletion of this hydrophobic domain (mutant dt) of E1 resulted in a disruption of the E1 conformation that ultimately affected E1-E2 heterodimer formation and cell surface expression of both E1 and E2. Substitution of either aspartic acid at Gly93 (G93D) or glycine at Pro104 (P104G) was found to impair neither E1-E2 heterodimer formation nor the transport of E1 and E2 to the cell surface. Fusion of RV-infected cells is induced by a brief treatment at a pH below 6. 0. To test whether this internal hydrophobic domain is involved in the membrane fusion activity of RV, transformed BHK cell lines expressing either wild-type or mutant spike proteins were exposed to an acidic pH and polykaryon formation was measured. No fusion activity was observed in the C82S, dt, and G93D mutants; however, the wild type and the P104G mutant exhibited fusogenic activities, with greater than 60% and 20 to 40% of the cells being fused, respectively, at pH 4.8. These results suggest that it is likely that the region of E1 between amino acids 81 and 109 is involved in the membrane fusion activity of RV and that it may be important for the interaction of that protein with E2 to form the E1-E2 heterodimer.
风疹病毒（RV）病毒粒子包含两种糖基化膜蛋白E1和E2，它们以异源二聚体形式存在，并在病毒粒子表面形成病毒刺突复合体。E1-E2异源二聚体的形成是E1从内质网腔转运至高尔基体和质膜所必需的。为了研究E1-E2相互作用的本质，我们在E1的内部疏水区域（第81至109位氨基酸残基）引入了突变。E1的Cys82位点丝氨酸替代（突变体C82S）或该疏水结构域缺失（突变体dt）导致E1构象破坏，最终影响E1-E2异源二聚体形成以及E1和E2在细胞表面的表达。发现Gly93位点天冬氨酸替代（G93D）或Pro104位点甘氨酸替代（P104G）既不损害E1-E2异源二聚体形成，也不影响E1和E2向细胞表面的转运。RV感染细胞的融合是通过在pH低于6.0的条件下短暂处理诱导的。为了测试该内部疏水结构域是否参与RV的膜融合活性，将表达野生型或突变型刺突蛋白的转化BHK细胞系暴露于酸性pH下，并检测多核体形成情况。在C82S、dt和G93D突变体中未观察到融合活性；然而，野生型和P104G突变体表现出融合活性，在pH 4.8时分别有超过60%和20%至40%的细胞发生融合。这些结果表明，E1的第81至109位氨基酸区域可能参与RV的膜融合活性，并且对于该蛋白与E2相互作用形成E1-E2异源二聚体可能很重要。
