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

白细胞介素-5（IL-5）是一种经典的TH 2细胞因子，在嗜酸性粒细胞生命的几乎任何方面都起着关键作用，从祖细胞的分化、迁移、增殖到其活化。因此，IL-5信号传导的失调表现在嗜酸性粒细胞过多性疾病的发展和进展中，所述疾病的特征在于嗜酸性粒细胞大量增殖和浸润到不同的组织和器官中，其中嗜酸性粒细胞活化可随后导致器官的严重损伤。因此，IL-5已成为治疗性干预疾病如过敏性哮喘、嗜酸性粒细胞性食管炎、嗜酸性粒细胞增多性疾病或Churg-Strauss综合征的主要靶标。抗IL-5中和抗体可缓解胃肠道嗜酸性粒细胞增多综合征的疾病症状。已经开发了阻断IL-5受体活化的短环肽，这可能为抗IL-5治疗提供了更具成本效益的策略。因此，深入了解IL-5信号转导的分子机制是开发或改善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-5 R α结合的二元复合物的晶体结构，在理解这一问题的分子机制方面迈出一大步。该结构显示了IL 5 R α：IL-5与扳手IL-5 R α相互作用的新的不寻常结构，该扳手IL-5 R α包围螺母IL-5。与体外相互作用分析一致的诱变揭示了IL-5 R α：IL-5相互作用的功能表位，表明受体的三个纤连蛋白III型结构域中的第一个包含受体-配体相互作用的热点。然而，IL-5的信号传导需要形成与IL-5 R α结合的IL-5和亚基共同-β的三元复合物，后者与IL-3和GM-CSF共享。然而，最近对GM-CSF的三元配体-受体复合物的分析挑战了配体仅二聚化两个受体亚基以启动信号转导的范例。而不是受体异源二聚体，形成更高阶的复合物，提出了如何提供配体特异性信号的问题。为了深入了解IL-5受体活化和与GM-CSF的潜在差异，我们提出了完整的、具有信号传导能力的三元IL-5：IL-5 R α：共同-β复合物的结构分析。与此同时，我们计划解决与IL-5 R α结合的基于肽的IL-5抑制剂的结构，以深入了解其抑制机制，然后将允许设计新的肽模拟物或改进这些肽。该项目试图全面了解IL-5复合物形成和信号激活的机制，目标是促进可能基于小分子化合物，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.