Ternary ligand-receptor complex formation by IL-5 and its inhibition by small peptides

白介素5(IL-5)是一种经典的TH2细胞因子，在嗜酸性粒细胞生活的几乎所有方面都发挥着关键作用，从祖细胞的分化、迁移、增殖到它们的激活。因此，IL-5信号的失控表现在高嗜酸性粒细胞疾病的发生和发展中，其特征是嗜酸性粒细胞大量增殖和渗透到不同的组织和器官中，其中嗜酸性粒细胞的激活可以导致器官的严重损害。因此，IL-5已成为过敏性哮喘、嗜酸性食管炎、高嗜酸性疾病或Churg-Strauss综合征等疾病治疗干预的主要靶点。抗IL-5中和抗体在影响胃肠道的高嗜酸性粒细胞综合征中表现出缓解症状。阻断IL-5受体激活的短环肽已经被开发出来，潜在地为抗IL-5治疗提供了一种更经济有效的策略。因此，深入了解IL-5信号转导的分子机制是开发或改进可能对抗这些疾病的IL-5抑制剂的先决条件。最近，我们可以通过解决IL-5与其受体IL-5Rα结合的二元络合物的晶体结构，在了解这种疾病的分子机制方面迈出一大步。该结构显示了IL-5Rpha的一个新的不寻常的结构：IL-5与包含坚果IL-5的扳手IL-5Rpha的相互作用。突变结合体外相互作用分析揭示了IL-5Rα：IL-5相互作用的功能表位，表明受体的三个纤维连接蛋白III型结构域中的第一个构成了受体-配体相互作用的热点。然而，IL-5的信号传递需要形成IL-5与IL-5Ra结合的三元复合体和共同的β亚基，后者与IL-3和GM-CSF共享。然而，最近对GM-CSF的三元配体-受体复合体的分析挑战了配体只将两个受体亚基二聚化来启动信号转导的范式。形成的不是受体异二聚体，而是更高阶的复合体，这引发了一个问题，即配体特异性信号是如何提供的。为了深入了解IL-5受体的激活及其与GM-CSF的潜在差异，我们建议对完整的、具有信号功能的三元IL-5：IL-5Rpha：公共-β复合体的结构进行分析。同时，我们计划解决基于多肽的IL-5抑制剂与IL-5Rpha结合的结构，提供对其抑制机制的洞察，这将允许设计新的多肽模拟物或提纯这些多肽。本项目试图对IL-5复合体的形成和信号激活的机制有一个全面的了解，目的是促进基于小分子化合物、多肽或突变蛋白的新型IL-5抑制剂的产生。

Interleukin-5 (IL-5) is a classical TH2 cytokine playing a pivotal role in almost any aspect of eosin-ophil life, starting with differentiation from progenitor cells, migration, proliferation to their activation. Thus deregulation of IL-5 signaling manifests in development and progression of hypereosinophilic diseases characterized by massive proliferation and infiltration of eosinophils into different tissues and organs, where eosinophil activation can subsequently lead to severe damage of the organ. Thus IL-5 has become a major target for therapeutic intervention in diseases such as allergic asthma, eosinophilic esophagitis, hypereosinophilic diseases or the Churg-Strauss syndrome. Anti-IL-5 neutralizing antibodies have shown relieve from disease symptoms in hypereosinophilic syn-dromes affecting the gastrointestinal tract. Short cyclic peptides blocking IL-5 receptor activation have been developed potentially providing a more cost-effective strategy for an anti-IL-5 therapy. Thus an in-depth understanding of the molecular mechanism underlying IL-5 signaling is a prereq-uisite for the development or improvement of IL-5 inhibitors possibly counteracting these diseases. Recently we could make a huge step towards understanding the molecular mechanism of this is-sue by solving the crystal structure of the binary complex of IL-5 bound to its receptor IL-5Ralpha. The structure shows a new unusual architecture for the IL 5Ralpha:IL-5 interaction with the wrench IL-5Ralpha encompassing the nut IL-5. Mutagenesis in concert with in vitro interaction analysis revealed the functional epitope for the IL-5Ralpha:IL-5 interaction showing that the first of the three Fibronectin type III domains of the receptor comprising the hotspot of the receptor-ligand interaction. However, signaling of IL-5 requires formation of a ternary complex of IL-5 bound to IL-5Ralpha and the subunit common-beta, the latter of which is shared with IL-3 and GM-CSF. Recent analyses of the ternary ligand-receptor complex of GM-CSF however challenged the paradigm of the ligand just dimerizing two receptor subunits to initiate signal transduction. Rather than a receptor heterodimer a higher-order complex is formed raising the question how ligand-specific signals are provided. To gain insight into the IL-5 receptor activation and potential differences to that of GM-CSF we propose structure analysis of the full, signaling-competent ternary IL-5:IL-5Ralpha:common-beta complex. In parallel, we plan to solve structures of peptide-based IL-5 inhibitors bound to IL-5Ralpha providing an insight into their inhibition mechanism, which will then allow to design new peptidomimetics or refine these peptides. This project attempts to get a comprehensive view on the mechanisms of IL-5 complex formation and signal activation with the goal to facilitate the generation of novel IL-5 inhibitors that might be based on small compounds, peptides or mutant proteins.