Contributions of interfacial residues of human Interleukin15 to the specificity and affinity for its private alpha-receptor
Contributions of interfacial residues of human Interleukin15 to the specificity and affinity for its private alpha-receptor
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人白介素 15 的界面残基对其私有 α 受体的特异性和亲和力的贡献
DOI：
10.1016/j.jmb.2009.04.050
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Kudou M and Tsumoto K
中科院分区：
文献类型：
--
作者：
Sakamoto S;Jose M. M. Caaveiro;Sano E;Tanaka Y;Kudou M and Tsumoto K
人白细胞介素15（human interleukin 15，hIL 15）是一种可溶性细胞因子，在维持机体对病原体的持久免疫应答中发挥重要作用，是治疗自身免疫性疾病的重要靶点。在本研究中，我们试图阐明其私人α-受体（hIL 15 R α）的识别机制的热力学基础，被认为是白细胞介素激活途径的第一步。野生型hIL 15与其α受体结合的特征是解离速率常数非常慢，并由有利的焓变驱动。我们进一步研究了动力学和能量的后果取代残基的hIL 15位于接触界面的表面等离子体共振技术的装置。用Ala取代带负电荷的残基表明相互作用的能量学主要由静电力驱动，表现为解离步骤的急剧加速和有利的结合焓的降低。我们的分析还揭示了残基Tyr 26在相互作用中的一个新的和关键的作用，这有助于在组装复合物过程中的关键带电残基的去溶剂化。这些结果与先前报道的hIL 15·hIL 15 α的结构有关，表明结合能主要由发生在三个热点的相互作用决定，这些热点的空间位置与先前提出的接触界面三个区域的结构划分相一致。具体而言，区域1是通过与受体建立非常有利的静电相互作用而对复合物的结合能做出主要贡献的区域;区域2也由静电力主导，尽管强度较小;并且区域3通过高形状互补性和通过为复合物带来额外的稳定能量而赋予缔合特异性。在基于细胞的增殖试验中评价了对α受体结合影响最大的hIL 15突变的生物学影响，验证了我们的热力学分析结论，并强调了促进白细胞介素与α受体长期结合的分子接触的功能重要性。最后，在IL 15 h·IL 15 R α复合物中观察到的相互作用的热力学和物理化学性质，以及白细胞介素3区中的相互作用，与结构相关且有时功能冗余的白细胞介素2形成鲜明对比。
Human interleukin 15 (hIL15) is a soluble cytokine that plays a key role in the maintenance of long-lasting responses against pathogens and a valuable target for the treatment of autoimmune diseases. In this study, we sought to elucidate the thermodynamic basis of the recognition mechanism for its private α-receptor (hIL15Rα), considered the first step of the interleukin's activation pathway. Binding of wild-type hIL15 to its α-receptor is characterized by a very slow dissociation rate constant and driven by a favorable enthalpy change. We further studied the kinetic and energetic consequences of substituting residues of hIL15 located at the contact interface by means of the surface plasmon resonance technique. Replacement of negatively charged residues with Ala indicates that the energetics of interaction is primarily driven by electrostatic forces, manifested by a dramatic acceleration of the dissociation step and a reduction of favorable binding enthalpy. Our analyses also unveiled a novel and critical role for residue Tyr26 in the interaction, which facilitates desolvation of key charged residues during the assembly of the complex. These results were rationalized in terms of a previously reported structure of hIL15·hIL15α, demonstrating that the binding energetics is dominated by interactions occurring at three hot spots whose spatial locations coincide with a previously proposed structural division of the contact interface in three regions. Specifically, Region 1 is the main contributor to the binding energy of the complex by establishing very favorable electrostatic interactions with the receptor; Region 2 is also dominated by electrostatic forces, although of a lesser intensity; and Region 3 confers specificity to the association by means of high shape complementarity and by bringing additional stabilization energy to the complex. The biological impact of hIL15 mutations with the most effect on α-receptor binding was evaluated in a cell-based proliferation assay, validating the conclusions of our thermodynamic analyses and highlighting the functional importance of molecular contacts that promote prolonged binding of the interleukin to the α-receptor. In closing, the thermodynamics and physicochemical nature of the interactions observed in IL15h·IL15Rα complex, together with interactions in Region 3 of the interleukin, poses a stark contrast with the structurally related and sometimes functionally redundant interleukin 2.