趋化因子受体CXCR4的结构与功能

目的 认识趋化因子受体CXCR4之结构与功能的关系。方法 分别建立野生型趋化因子受体CXCR4及CXCR2、5个CXCR4/CXCR2嵌合受体和2个CXCR4突变受体的CHO稳定表达细胞株，以配体-受体结合试验，细胞微生理监测术、体外细胞-细胞融合实验为手段观察各变异受体与重组人SDF-1β的结合能力、在受刺激后的信号转导能力，以及作为HIV-1辅助受体的能力。结果 有4个变异受体（2444a,4442,4222,CXCR4-Tr）保持了程度不同的具有辅助受体功能。结论 CXCR4以多个结构区域参与与SDF-1β的相互作用。其N端胞外区足以及具有与SDF-1β的高亲和性结合能力。第三环链对CXCR4的结合能力也具有其特定的贡献。CXCR4的信号传导不仅需要保守结构DRY盒，而且还需要贯穿整个分子的7个跨膜区域和受配体刺激后形成并维持一定的构象。CXCR4的辅助受体功能结构域与配体结合结构域间存在交叉重叠。

Structure-function correlation of chemokine receptor CXCR4

Objective　To explore the correlation between structure domains and function of chemokine receptor CXCR4. Methods　After the establishment of wild type chemokine receptor CXCR4 and CXCR2, 5 CXCR4/CXCR2 chimeras, 2 CXCR4 mutants stably expressed on CHO cell line, all variants' bound activity with the ligant recombinant human SDF-1β，signal transduction ability after stimulation and their function as coreceptor for HIV-1 were studied with ligand-binding assay, cytosensor/microphysiometry and cell-cell receptor gene fusion assay. Results　Among all 7 changed CXCR4 receptors, 3 chimeras (2444a, 4442, 4222) and 1 mutant (CXCR4-Tr) could be bound with SDF-1β in various degrees, of which only 2444a totally and CXCR4-Tr partially maintained signaling. All changed receptors but 4222 could act as coreceptors for HIV-1 (LA1) in varying degrees. Conclusion　Several structure domains of CXCR4 are involved in the binding with SDF-1β. Among these domains, N-terminal extracellular domain has high affinity bound capability with SDF-1β, and the 3rd extracellular loop contributes to the binding too. Although the C-terminal intracellular domain has no association with the maintenance of the overall structure of the receptor and the ligand bound capability, the signaling is decreased when this domain is truncated. For CXCR4 signaling, not only the conserved motif DRY box is needed, but also the characterized conformation of the whole molecule must be formed when activation is required. There are some overlaps between SDF-1β bound domains and coreceptor funtion domain in molecular structure of CXCR4.