Stable exposure of the coreceptor-binding site in a CD4-independent HIV-1 envelope protein
Stable exposure of the coreceptor-binding site in a CD4-independent HIV-1 envelope protein
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DOI：
10.1073/pnas.96.11.6359
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发表时间：
1999-05-25
影响因子：
11.1
通讯作者：
Doms, RW
中科院分区：
文献类型：
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作者：
Hoffman, TL;LaBranche, CC;Doms, RW
我们最近从HIV-1/IIIB中获得了一种不依赖cd4的病毒，称为IIIBx，它直接与趋化因子受体CXCR4相互作用以感染细胞。为了解决潜在的机制，从IIIBx群（8x）克隆的Env被用来产生可溶性gp120, 8x gp120直接结合到只表达CXCR4的细胞上，而IIIB gp120的结合需要可溶性CD4。使用光学生物传感器，我们发现CD4诱导的CD4i表位在8x上比在IIIB gp120上更多地暴露。在没有CD4的情况下，8x gp120能够直接与CXCR4结合并与mab 17b和48d发生反应，这表明该gp120存在于部分触发但稳定的状态，在这种状态下，gp120中保守的与17b表位重叠的辅助受体结合位点暴露出来。将8x V3环与R5病毒株Bat的环替换，得到介导CD4非依赖性ccr5依赖性病毒感染的Env （8x- v3bal）和在缺乏CD4时结合CCRS的gp120。因此，在部分触发的Env蛋白中，V3环可以改变辅助受体使用的特异性，但不改变CD4的独立性，表明这些特性是可分离的。最后，IIIBx对hiv阳性的人血清、多种抗iiibb gp120兔血清和CD4i单抗的中和反应比IIIB更敏感。这种病毒对中和的敏感性和gp120高度保守区域的稳定暴露，为开发针对这一重要功能域的抗体和小分子抑制剂提供了新的策略。
We recently derived a CD4-independent virus from HIV-1/IIIB, termed IIIBx, which interacts directly with the chemokine receptor CXCR4 to infect cells. To address the underlying mechanism, a cloned Env from the IIIBx swarm (8x) was used to produce soluble gp120, 8x gp120 bound directly to cells expressing only CXCR4, whereas binding of IIIB gp120 required soluble CD4, Using an optical biosensor, we found that CD4-induced (CD4i) epitopes recognized by mAbs 17b and 48d were more exposed on 8x than on IIIB gp120, The ability of 8x gp120 to bind directly to CXCR4 and to react with mAbs 17b and 48d in the absence of CD4 indicated that this gp120 exists in a partially triggered but stable state in which the conserved coreceptor-binding site in gp120, which overlaps with the 17b epitope, is exposed. Substitution of the 8x V3 loop with that from the R5 virus strain Bat resulted in an Env (8x-V3BaL) that mediated CD4-independent CCR5-dependent virus infection and a gp120 that bound to CCRS in the absence of CD4. Thus, in a partially triggered Env protein, the V3 loop can change the specificity of coreceptor use but does not alter CD4 independence, indicating that these properties are dissociable, Finally, IIIBx was more sensitive to neutralization by HIV-positive human sera, a variety of anti-IIIB gp120 rabbit sera, and CD4i mAbs than was IIIB, The sensitivity of this virus to neutralization and the stable exposure of a highly conserved region of gp120 suggest new strategies for the development of antibodies and small molecule inhibitors to this functionally important domain.