Mach M, Kropff B, Dal Monte P, Britt W
Institut für Klinische und Molekulare Virologie, Universität Erlangen-Nürnberg, Erlangen, Germany.
J Virol. 2000 Dec;74(24):11881-92. doi: 10.1128/jvi.74.24.11881-11892.2000.
The envelope glycoproteins of human cytomegalovirus (HCMV) virions are incompletely characterized. We have analyzed complex formation between glycoprotein M (gM or gpUL100) and a second glycoprotein. gM-homologous proteins are conserved throughout the herpesvirus family and represent type III membrane proteins containing multiple hydrophobic sequences. In extracellular HCMV particles, gM was found to be complexed through disulfide bonds to a second protein with an apparent molecular mass of 50 to 60 kDa. The 50- to 60-kDa protein was found to be derived from reading frame UL73 of HCMV strain AD169. UL73-homologous genes are also conserved within herpesviruses. When transiently expressed by itself, the UL73 gene product consisted of a protein of 18 kDa. However, in the presence of gM, the UL73 gene product was posttranslationally modified to the 50- to 60-kDa species. Thus, gM and the UL73 gene product, which represents the gN homolog of herpesviruses, form a disulfide-linked complex in HCMV virions. Transient expression of gM and gN followed by fluorescence imaging with monoclonal antibodies against either protein demonstrated that complex formation was required for transport of the proteins from the endoplasmic reticulum to the Golgi and trans-Golgi compartments. Finally, we tested the gM-gN complex for reactivity with sera from HCMV-seropositive donors. Whereas most sera failed to react with either gM or gN when expressed alone, 62% of sera were positive for the gM-gN complex. Because a murine monoclonal antibody reactive with gN in the gM-gN complex efficiently neutralizes infectious virus, the gM-gN complex may represent a major antigenic target of antiviral antibody responses.
人巨细胞病毒（HCMV）病毒粒子的包膜糖蛋白尚未得到充分表征。我们分析了糖蛋白M（gM或gpUL100）与另一种糖蛋白之间的复合物形成。gM同源蛋白在整个疱疹病毒家族中保守，代表含有多个疏水序列的III型膜蛋白。在细胞外HCMV颗粒中，发现gM通过二硫键与一种表观分子量为50至60 kDa的第二种蛋白形成复合物。发现50至60 kDa的蛋白源自HCMV AD169株的阅读框UL73。UL73同源基因在疱疹病毒中也保守。当单独瞬时表达时，UL73基因产物由18 kDa的蛋白组成。然而，在gM存在下，UL73基因产物在翻译后被修饰为50至60 kDa的物种。因此，gM和代表疱疹病毒gN同源物的UL73基因产物在HCMV病毒粒子中形成二硫键连接的复合物。gM和gN的瞬时表达，随后用针对任一蛋白的单克隆抗体进行荧光成像，表明复合物形成是蛋白质从内质网转运到高尔基体和反式高尔基体区室所必需的。最后，我们测试了gM-gN复合物与HCMV血清阳性供体血清的反应性。虽然大多数血清在单独表达时与gM或gN均无反应，但62%的血清对gM-gN复合物呈阳性。由于一种与gM-gN复合物中的gN反应的鼠单克隆抗体能有效中和感染性病毒，gM-gN复合物可能代表抗病毒抗体反应的主要抗原靶点。
