he human immunodeficiency virus type 1 (HIV-1) recognizes one of its principal coreceptors, the CXC chemokine receptor 4 (CXCR4) on the host cell via the third variable loop (V3 loop) of HIV-1 envelope glycoprotein gp120 during the viral entry process. Here, we investigated the stereochemical mechanism of the molecular recognition of HIV-1 gp120 V3 loop with coreceptor CXCR4 by using peptide probes containing important fragments of the V3 loop. The tip and base/stem fragments of the V3 loop critical for V3 loop function were linked individually with the fragment derived from another CXCR4's chemokine ligand, vMIP-II to generate nanomolar affinity peptide probes of the interactions of CXCR4-V3 loop fragments. When the amino acid residues of the V3 loop fragments in these combinational peptides were changed from L-to D-configurations, the resulting peptides remarkably retained or had even enhanced recognition by CXCR4 as shown by competitive ligand-receptor binding. The ability of these peptides, regardless of the different l- or d-amino acids used, in binding CXCR4 and antagonizing CXCR4 functions was demonstrated by their blockade of calcium influx, cell migration, and CXCR4 internalization triggered by the activation of CXCR4 signaling by its endogenous ligand SDF-1α. The structural mechanisms of CXCR4 interactions with these peptides were examined with site-directed mutagenesis and molecular modeling. These results indicate that CXCR4's interface with key segments of HIV-1 gp120 V3 loop is flexible in terms of stereospecificity of ligand-receptor interaction which may have implication on understanding the viral entry mechanism and how the virus evades immune detection with V3 loop mutations and retains effective recognition of the host cell's coreceptor.

人类免疫缺陷病毒 1 型 (HIV-1) 在病毒进入期间通过 HIV-1 包膜糖蛋白 gp120 的第三个可变环（V3 环）识别其主要辅助受体之一，即宿主细胞上的 CXC 趋化因子受体 4 (CXCR4)过程。在这里，我们通过使用含有 V3 环重要片段的肽探针研究了 HIV-1 gp120 V3 环与辅助受体 CXCR4 分子识别的立体化学机制。对 V3 环功能至关重要的 V3 环的尖端和基/茎片段分别与源自另一个 CXCR4 的趋化因子配体 vMIP-II 的片段连接，以生成 CXCR4-V3 环片段相互作用的纳摩尔亲和肽探针。当这些组合肽中 V3 环片段的氨基酸残基从 L-构型变为 D-构型时，如竞争性配体-受体结合所示，由此产生的肽显着保留甚至增强了 CXCR4 的识别。这些肽的能力，无论不同在结合 CXCR4 和拮抗 CXCR4 功能中使用的 l - 或 d - 氨基酸通过其阻断钙流入、细胞迁移和由其内源性配体 SDF-1α 激活 CXCR4 信号转导触发的 CXCR4 内化来证明。CXCR4 与这些肽相互作用的结构机制通过定点诱变和分子建模进行了检查。这些结果表明，CXCR4 与 HIV-1 gp120 V3 环的关键片段的界面在配体-受体相互作用的立体特异性方面是灵活的，这可能对理解病毒进入机制以及病毒如何通过 V3 环突变逃避免疫检测和保留具有重要意义有效识别宿主细胞的辅助受体。