Siciliano S J, Kuhmann S E, Weng Y, Madani N, Springer M S, Lineberger J E, Danzeisen R, Miller M D, Kavanaugh M P, DeMartino J A, Kabat D
Merck Research Laboratories, Immunology and Rheumatology, Rahway, New Jersey 07065, USA.
J Biol Chem. 1999 Jan 22;274(4):1905-13. doi: 10.1074/jbc.274.4.1905.
Like the CCR5 chemokine receptors of humans and rhesus macaques, the very homologous (approximately 98-99% identical) CCR5 of African green monkeys (AGMs) avidly binds beta-chemokines and functions as a coreceptor for simian immunodeficiency viruses. However, AGM CCR5 is a weak coreceptor for tested macrophage-tropic (R5) isolates of human immunodeficiency virus type 1 (HIV-1). Correspondingly, gp120 envelope glycoproteins derived from R5 isolates of HIV-1 bind poorly to AGM CCR5. We focused on a unique extracellular amino acid substitution at the juncture of transmembrane helix 4 (TM4) and extracellular loop 2 (ECL2) (Arg for Gly at amino acid 163 (G163R)) as the likely source of the weak R5 gp120 binding and HIV-1 coreceptor properties of AGM CCR5. Accordingly, a G163R mutant of human CCR5 was severely attenuated in its ability to bind R5 gp120s and to mediate infection by R5 HIV-1 isolates. Conversely, the R163G mutant of AGM CCR5 was substantially strengthened as a coreceptor for HIV-1 and had improved R5 gp120 binding affinity relative to the wild-type AGM CCR5. These substitutions at amino acid position 163 had no effect on chemokine binding or signal transduction, suggesting the absence of structural alterations. The 2D7 monoclonal antibody has been reported to bind to ECL2 and to block HIV-1 binding and infection. Whereas 2D7 antibody binding to CCR5 was unaffected by the G163R mutation, it was prevented by a conservative ECL2 substitution (K171R), shared between rhesus and AGM CCR5s. Thus, it appears that the 2D7 antibody binds to an epitope that includes Lys-171 and may block HIV-1 infection mediated by CCR5 by occluding an HIV-1-binding site in the vicinity of Gly-163. In summary, our results identify a site for gp120 interaction that is critical for R5 isolates of HIV-1 in the central core of human CCR5, and we propose that this site collaborates with a previously identified region in the CCR5 amino terminus to enable gp120 binding and HIV-1 infections.
与人类和恒河猴的CCR5趋化因子受体一样，非洲绿猴（AGM）的CCR5与之高度同源（约98 - 99%相同），能 avidly 结合β趋化因子，并作为猿猴免疫缺陷病毒的共受体发挥作用。然而，AGM CCR5对于经测试的1型人类免疫缺陷病毒（HIV - 1）的巨噬细胞嗜性（R5）分离株而言是一种较弱的共受体。相应地，源自HIV - 1的R5分离株的gp120包膜糖蛋白与AGM CCR5的结合较差。我们聚焦于跨膜螺旋4（TM4）和细胞外环2（ECL2）交界处的一个独特的细胞外氨基酸替换（氨基酸163处的甘氨酸被精氨酸取代（G163R）），认为这可能是AGM CCR5与R5 gp120结合较弱以及HIV - 1共受体特性的原因。因此，人CCR5的G163R突变体在结合R5 gp120以及介导R5 HIV - 1分离株感染的能力上严重减弱。相反，AGM CCR5的R163G突变体作为HIV - 1的共受体得到显著增强，并且相对于野生型AGM CCR5，其R5 gp120结合亲和力有所提高。氨基酸位置163处的这些替换对趋化因子结合或信号转导没有影响，表明不存在结构改变。据报道，2D7单克隆抗体可结合ECL2并阻断HIV - 1的结合和感染。虽然2D7抗体与CCR5的结合不受G163R突变的影响，但恒河猴和AGM CCR5共有的ECL2保守替换（K171R）可阻止其结合。因此，似乎2D7抗体结合到一个包含赖氨酸 - 171的表位，并且可能通过封闭甘氨酸 - 163附近的HIV - 1结合位点来阻断CCR5介导的HIV - 1感染。总之，我们的结果确定了一个gp120相互作用位点，该位点对于HIV - 1的R5分离株在人CCR5的中心核心区域至关重要，并且我们提出该位点与CCR5氨基末端先前确定的区域协同作用，以实现gp120结合和HIV - 1感染。
