CCR5 Conformations Are Dynamic and Modulated by Localization, Trafficking and G Protein Association

CCR5 acts as the principal coreceptor during HIV-1 transmission and early stages of infection. Efficient HIV-1 entry requires a series of processes, many dependent on the conformational state of both viral envelope protein and cellular receptor. Monoclonal antibodies (MAbs) are able to identify different CCR5 conformations, allowing for their use as probes to distinguish CCR5 populations. Not all CCR5 MAbs are able to reduce HIV-1 infection, suggesting the use of select CCR5 populations for entry. In the U87.CD4.CCR5-GFP cell line, we used such HIV-1-restricting MAbs to probe the relation between localization, trafficking and G protein association for individual CCR5 conformations. We find that CCR5 conformations not only exhibit different localization and abundance patterns throughout the cell, but that they also display distinct sensitivities to endocytosis inhibition. Using chemokine analogs that vary in their HIV-1 inhibitory mechanisms, we also illustrate that responses to ligand engagement are conformation-specific. Additionally, we provide supporting evidence for the select sensitivity of conformations to G protein association. Characterizing the link between the function and dynamics of CCR5 populations has implications for understanding their selective targeting by HIV-1 and for the development of inhibitors that will block CCR5 utilization by the virus.

CC趋化因子受体5（CCR5）是HIV-1传播及感染早期阶段的主要共受体。高效的HIV-1入侵需要一系列步骤，其中多数依赖于病毒包膜蛋白与细胞受体的构象状态。单克隆抗体（MAbs）可识别不同的CCR5构象，因此可作为探针区分CCR5群体。并非所有靶向CCR5的单克隆抗体都能抑制HIV-1感染，这表明病毒仅利用特定的CCR5群体完成入侵。本研究在U87.CD4.CCR5-GFP细胞系中，利用这类可抑制HIV-1的单克隆抗体，探究了单个CCR5构象的定位、转运与G蛋白结合之间的关联。研究发现，CCR5的不同构象不仅在细胞内呈现出各异的定位与丰度模式，还对胞吞抑制表现出不同的敏感性。我们采用了HIV-1抑制机制各异的趋化因子类似物，证实配体结合后的应答反应具有构象特异性。此外，本研究为不同构象对G蛋白结合的选择性敏感性提供了佐证。阐明CCR5群体的功能与动态之间的关联，有助于理解HIV-1对其的选择性靶向机制，同时可为开发阻断病毒利用CCR5的抑制剂提供理论依据。