Stauber R, Pfleiderer M, Siddell S
Institut für Virologie, Universität Würzburg.
Adv Exp Med Biol. 1993;342:165-70. doi: 10.1007/978-1-4615-2996-5_26.
The surface glycoprotein (S) of the murine hepatitis coronavirus MHV normally undergoes proteolytic cleavage during transport to the cell surface. To determine whether the cleavage of the MHV-JHM S glycoprotein is required to activate its ability to fuse cellular membranes, the protease recognition sequence in a cDNA copy of the S gene was altered from Arg-Arg-Ala-Arg-Arg into Ser-Val-Ser-Gly-Gly by site directed mutagenesis. The mutated and wild type S genes were expressed by means of recombinant vaccinia viruses and it could be shown that the mutated S protein was not cleaved when it was expressed in mouse DBT cells, in contrast to the wild type S protein. Nevertheless, the non-cleaved S protein induced extensive syncytium formation in mouse DBT cells. These results clearly indicate that the non-cleaved form of the MHV S protein is able to mediate cell membrane fusion. Thus, proteolytic cleavage is not an absolute requirement for its fusion function.
鼠肝炎冠状病毒MHV的表面糖蛋白（S）通常在转运至细胞表面的过程中发生蛋白水解切割。为了确定MHV-JHM S糖蛋白的切割是否是激活其融合细胞膜能力所必需的，通过定点诱变将S基因cDNA拷贝中的蛋白酶识别序列从精氨酸-精氨酸-丙氨酸-精氨酸-精氨酸改变为丝氨酸-缬氨酸-丝氨酸-甘氨酸-甘氨酸。突变型和野生型S基因通过重组痘苗病毒进行表达，结果表明，与野生型S蛋白不同，突变型S蛋白在小鼠DBT细胞中表达时未被切割。然而，未切割的S蛋白在小鼠DBT细胞中诱导了广泛的合胞体形成。这些结果清楚地表明，MHV S蛋白的未切割形式能够介导细胞膜融合。因此，蛋白水解切割并非其融合功能的绝对必要条件。
