Bedgood R M, Stallcup M R
Department of Pathology, University of Southern California Health Sciences Center, Los Angeles 90033.
J Biol Chem. 1992 Apr 5;267(10):7060-5.
The intracellular processing of the murine leukemia virus envelope glycoprotein precursor Pr85 to the mature products gp70 and p15e was analyzed in the mouse T-lymphoma cell line W7MG1. Kinetic (pulse-chase) analysis of synthesis and processing, coupled with endoglycosidase (endo H) and neuraminidase digestions revealed the existence of a novel high molecular weight processing intermediate, gp95, containing endo H-resistant terminally glycosylated oligosaccharide chains. In contrast to previously published conclusions, our data indicate that proteolytic cleavage of the envelope precursor occurs after the acquisition of endo H-resistant chains and terminal glycosylation and thus after the mannosidase II step. In the same W7MG1 cell line, the type and order of murine leukemia virus envelope protein processing events was identical to that for the mouse mammary tumor virus envelope protein. Interestingly, complete mouse mammary tumor virus envelope protein processing requires the addition of glucocorticoid hormone, whereas murine leukemia virus envelope protein processing occurs constitutively in these W7MG1 cells. We propose that all retroviral envelope proteins share a common processing pathway in which proteolytic processing is a late event that follows acquisition of endo H resistance and terminal glycosylation.
在小鼠T淋巴瘤细胞系W7MG1中分析了鼠白血病病毒包膜糖蛋白前体Pr85向成熟产物gp70和p15e的细胞内加工过程。对合成和加工过程进行动力学（脉冲追踪）分析，并结合内切糖苷酶（内切酶H）和神经氨酸酶消化，揭示了一种新型高分子量加工中间体gp95的存在，其含有对内切酶H有抗性的末端糖基化寡糖链。与先前发表的结论相反，我们的数据表明，包膜前体的蛋白水解切割发生在获得对内切酶H有抗性的链和末端糖基化之后，因此是在甘露糖苷酶II步骤之后。在同一W7MG1细胞系中，鼠白血病病毒包膜蛋白加工事件的类型和顺序与小鼠乳腺肿瘤病毒包膜蛋白相同。有趣的是，完整的小鼠乳腺肿瘤病毒包膜蛋白加工需要添加糖皮质激素，而鼠白血病病毒包膜蛋白加工在这些W7MG1细胞中是组成性发生的。我们提出，所有逆转录病毒包膜蛋白都共享一条共同的加工途径，其中蛋白水解加工是在获得对内切酶H的抗性和末端糖基化之后的一个晚期事件。
