Zagouras P, Rose J K
Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Virol. 1993 Dec;67(12):7533-8. doi: 10.1128/JVI.67.12.7533-7538.1993.
Previous studies have shown that trimers of the vesicular stomatitis virus glycoprotein (VSV G protein) are in rapid equilibrium with monomeric subunits after folding and assembly in the endoplasmic reticulum (ER). To determine whether G protein trimers were in equilibrium with monomers in other cellular compartments, we studied heterotrimer formation between VSV G protein and a mutant G protein (G mu protein) containing a 3-amino-acid cytoplasmic domain replacing the normal 29-amino-acid domain. The G mu protein is transported from the ER much more slowly than G protein, although both G and G mu proteins form trimers rapidly in the ER. In coexpression experiments, we observed that VSV G protein molecules exited the ER about sixfold faster than G mu protein molecules, and we observed no heterotrimer formation in the ER, probably because of rapid reassortment of the mutant and wild-type trimers. However, heterotrimer formation between the two proteins was observed after long chase periods that allowed time for trimers of the mutant protein to reach the plasma membrane and reassort with the G protein subunits. Additional studies showed that heterotrimers of the two proteins could form in the Golgi or in the ER if exit of the G protein from either compartment was blocked.
先前的研究表明，水泡性口炎病毒糖蛋白（VSV G蛋白）三聚体在内质网（ER）中折叠和组装后，与单体亚基处于快速平衡状态。为了确定G蛋白三聚体在其他细胞区室中是否与单体处于平衡状态，我们研究了VSV G蛋白与一种突变G蛋白（Gμ蛋白）之间的异源三聚体形成，该突变G蛋白含有一个由3个氨基酸组成的细胞质结构域，取代了正常的29个氨基酸结构域。Gμ蛋白从内质网的转运速度比G蛋白慢得多，尽管G蛋白和Gμ蛋白在内质网中都能迅速形成三聚体。在共表达实验中，我们观察到VSV G蛋白分子从内质网中出来的速度比Gμ蛋白分子快约6倍，并且我们在内质网中未观察到异源三聚体的形成，这可能是由于突变体和野生型三聚体的快速重新组合。然而，在长时间追踪后观察到了两种蛋白之间的异源三聚体形成，这使得突变蛋白的三聚体有时间到达质膜并与G蛋白亚基重新组合。进一步的研究表明，如果G蛋白从任何一个区室的输出被阻断，两种蛋白的异源三聚体可以在高尔基体或内质网中形成。
