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

点击翻译按钮获取中文摘要

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.