Rajagopalan Lavanya, Rösgen Jörg, Bolen David Wayne, Rajarathnam Krishna
Department of Human Biological Chemistry and Genetics and Sealy Center for Structural Biology, The University of Texas Medical Branch, Galveston, Texas 77555-1055, USA.
Biochemistry. 2005 Oct 4;44(39):12932-9. doi: 10.1021/bi051219z.
We have used trimethylamine N-oxide (TMAO), a protecting osmolyte, to dissect the complex thermodynamic linkages involved in the interaction between the chemokine interleukin-8 (IL-8) and the N-domain of its receptor CXCR1. Our results show that TMAO induces folding in the CXCR1 receptor N-domain and that the N-domain upon folding binds ligand with higher affinity. This represents, to our knowledge, the smallest domain that has been shown to be folded in osmolyte. Using the phase diagram method to analyze this thermodynamic relationship graphically, we also observe that TMAO favors ligand dimerization and that the dimeric ligand binds the receptor domain with lower affinity. We have thus been able to dissect coupling among three distinct processes, receptor domain folding, ligand dimerization, and ligand-receptor domain binding in this chemokine-receptor system. We also observe that the affinity of the related chemokine, melanoma growth stimulatory activity (MGSA), increases concurrent with N-domain folding similar to IL-8 but shows more profound differences on ligand dimerization. These studies establish a novel and innovative use of osmolytes to dissect linkages among different processes and exploit the phase diagram as a tool to graphically represent and dissect complex thermodynamic relationships in biological systems. On the basis of our observations and earlier work, we discuss the relevance of ligand dimerization in chemokine regulation.
我们使用了一种具有保护作用的渗透溶质——氧化三甲胺（TMAO），来剖析趋化因子白细胞介素-8（IL-8）与其受体CXCR1的N结构域之间相互作用所涉及的复杂热力学联系。我们的结果表明，TMAO可诱导CXCR1受体N结构域发生折叠，且折叠后的N结构域与配体的结合亲和力更高。据我们所知，这是已被证明能在渗透溶质中折叠的最小结构域。通过相图法以图形方式分析这种热力学关系，我们还观察到TMAO有利于配体二聚化，且二聚体配体与受体结构域的结合亲和力较低。因此，我们得以剖析该趋化因子-受体系统中三个不同过程之间的耦合，即受体结构域折叠、配体二聚化以及配体-受体结构域结合。我们还观察到，相关趋化因子黑色素瘤生长刺激活性（MGSA）的亲和力随N结构域折叠而增加，这与IL-8类似，但在配体二聚化方面表现出更显著的差异。这些研究确立了渗透溶质在剖析不同过程之间联系方面的一种新颖且创新的应用，并利用相图作为一种工具来图形化表示和剖析生物系统中复杂的热力学关系。基于我们的观察结果和早期工作，我们讨论了配体二聚化在趋化因子调节中的相关性。
