Pinter A, Honnen W J
J Virol. 1984 Feb;49(2):452-8. doi: 10.1128/JVI.49.2.452-458.1984.
A detailed comparison of the gp70 proteins of cloned ecotropic Friend murine leukemia virus (FLV) and dual-tropic Friend mink focus-forming virus (FrMCF) was performed by analyzing the structural and immunological properties of amino- and carboxy-terminal domains of these molecules generated upon controlled trypsinization. The two gp70s gave characteristic fragmentation patterns; the amino-terminal fragments of FrMCF gp70 were smaller than the corresponding fragments of FLV and contained a trypsin site which resulted in a 19,000-dalton amino-terminal fragment not observed for FLV, whereas both molecules yielded an identically sized carboxy-terminal fragment. All amino-terminal fragments of both gp70 molecules contained an endo H-sensitive oligosaccharide chain; for FrMCF, a second endo H-sensitive carbohydrate was present as well at a carboxy-terminal site for approximately 50% of the molecules. Several aspects of the disulfide interactions of the two gp70s were conserved; in both cases the carboxy-terminal fragments were disulfide bonded to p15(E), there were no disulfide bonds between amino- and carboxy-terminal fragments, and the amino-terminal fragments exhibited a significant increase in mobility upon analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Analysis of the immunoreactivity of the different domains of the proteins by immunoprecipitation of the fragments with antisera prepared against xenotropic murine leukemia virus and feline leukemia virus gp70s indicated major differences in antigenicity for the amino-terminal domains of FLV and FrMCF gp70, whereas the carboxy-terminal domains were immunologically conserved. Similar analyses with antibodies specific for p15(E) and Pr15(E) demonstrate that these components are conserved as well. These data provide direct evidence that p15(E) and the C-terminal gp70 domain of FrMCF gp70 are related to the corresponding regions of the ecotropic FLV parent and indicate that the acquisition of MCF-specific properties is due to the replacement of the ecotropic amino-terminal gp70 domain with sequences related to those of xenotropic gp70s.
通过分析经可控胰蛋白酶消化产生的这些分子的氨基末端和羧基末端结构域的结构和免疫特性，对克隆的亲嗜性弗氏小鼠白血病病毒（FLV）和双嗜性弗氏水貂集落形成病毒（FrMCF）的gp70蛋白进行了详细比较。两种gp70呈现出特征性的片段化模式；FrMCF gp70的氨基末端片段比FLV的相应片段小，并且含有一个胰蛋白酶切割位点，该位点产生了一个19,000道尔顿的FLV未观察到的氨基末端片段，而两种分子产生的羧基末端片段大小相同。两种gp70分子的所有氨基末端片段都含有一条对内切糖苷酶H敏感的寡糖链；对于FrMCF，约50%的分子在羧基末端位点还存在第二个对内切糖苷酶H敏感的碳水化合物。两种gp70的二硫键相互作用的几个方面是保守的；在两种情况下，羧基末端片段都通过二硫键与p15(E)相连，氨基末端和羧基末端片段之间没有二硫键，并且在非还原条件下通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析时，氨基末端片段的迁移率显著增加。用针对异嗜性小鼠白血病病毒和猫白血病病毒gp70制备的抗血清对片段进行免疫沉淀，分析蛋白质不同结构域的免疫反应性，结果表明FLV和FrMCF gp70的氨基末端结构域在抗原性上存在主要差异，而羧基末端结构域在免疫上是保守的。用针对p15(E)和Pr15(E)的特异性抗体进行的类似分析表明，这些成分也是保守的。这些数据提供了直接证据，表明p15(E)和FrMCF gp70的C末端gp70结构域与亲嗜性FLV亲本的相应区域相关，并表明获得MCF特异性特性是由于亲嗜性氨基末端gp70结构域被与异嗜性gp70相关的序列所取代。
