Hoffman T L, LaBranche C C, Zhang W, Canziani G, Robinson J, Chaiken I, Hoxie J A, Doms R W
Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 1999 May 25;96(11):6359-64. doi: 10.1073/pnas.96.11.6359.
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 BaL resulted in an Env (8x-V3BaL) that mediated CD4-independent CCR5-dependent virus infection and a gp120 that bound to CCR5 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.
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。为了探究其潜在机制，我们使用从IIIBx群体（8x）中克隆的Env来产生可溶性gp120。8x gp120直接与仅表达CXCR4的细胞结合，而IIIB gp120的结合则需要可溶性CD4。使用光学生物传感器，我们发现单克隆抗体17b和48d识别的CD4诱导（CD4i）表位在8x上比在IIIB gp120上更易暴露。8x gp120在没有CD4的情况下直接结合CXCR4并与单克隆抗体17b和48d反应的能力表明，这种gp120以部分触发但稳定的状态存在，其中gp120中与17b表位重叠的保守共受体结合位点是暴露的。用R5病毒株BaL的V3环替换8x V3环，产生了一种Env（8x-V3BaL），它介导不依赖CD4的、依赖CCR5的病毒感染，以及一种在没有CD4的情况下与CCR5结合的gp120。因此，在部分触发的Env蛋白中，V3环可以改变共受体使用的特异性，但不会改变不依赖CD4的特性，这表明这些特性是可分离的。最后，与IIIB相比，IIIBx对HIV阳性人血清、多种抗IIIB gp120兔血清和CD4i单克隆抗体的中和作用更敏感。这种病毒对中和作用的敏感性以及gp120高度保守区域的稳定暴露，为针对这一功能重要结构域开发抗体和小分子抑制剂提供了新策略。
