RESUMO
Cytokines regulate immune responses by binding to cell surface receptors, including the common subunit beta (ßc), which mediates signaling for GM-CSF, IL-3, and IL-5. Despite known roles in inflammation, the structural basis of IL-5 receptor activation remains unclear. We present the cryo-EM structure of the human IL-5 ternary receptor complex, revealing architectural principles for IL-5, GM-CSF, and IL-3. In mammalian cell culture, single-molecule imaging confirms hexameric IL-5 complex formation on cell surfaces. Engineered chimeric receptors show that IL-5 signaling, as well as IL-3 and GM-CSF, can occur through receptor heterodimerization, obviating the need for higher-order assemblies of ßc dimers. These findings provide insights into IL-5 and ßc receptor family signaling mechanisms, aiding in the development of therapies for diseases involving deranged ßc signaling.
Assuntos
Microscopia Crioeletrônica , Fator Estimulador de Colônias de Granulócitos e Macrófagos , Interleucina-3 , Multimerização Proteica , Transdução de Sinais , Humanos , Fator Estimulador de Colônias de Granulócitos e Macrófagos/metabolismo , Fator Estimulador de Colônias de Granulócitos e Macrófagos/química , Fator Estimulador de Colônias de Granulócitos e Macrófagos/genética , Interleucina-3/metabolismo , Interleucina-3/química , Interleucina-3/genética , Células HEK293 , Ligação Proteica , Modelos Moleculares , Interleucina-5/metabolismo , Subunidade beta Comum dos Receptores de Citocinas/metabolismo , Subunidade beta Comum dos Receptores de Citocinas/genética , Subunidade beta Comum dos Receptores de Citocinas/química , Imagem Individual de Molécula , Relação Estrutura-Atividade , Sítios de Ligação , Receptores de Interleucina-5/metabolismo , Receptores de Interleucina-5/genética , Receptores de Interleucina-5/químicaRESUMO
Leptin is an adipocyte-derived protein hormone that promotes satiety and energy homeostasis by activating the leptin receptor (LepR)-STAT3 signaling axis in a subset of hypothalamic neurons. Leptin signaling is dysregulated in obesity, however, where appetite remains elevated despite high levels of circulating leptin. To gain insight into the mechanism of leptin receptor activation, here we determine the structure of a stabilized leptin-bound LepR signaling complex using single particle cryo-EM. The structure reveals an asymmetric architecture in which a single leptin induces LepR dimerization via two distinct receptor-binding sites. Analysis of the leptin-LepR binding interfaces reveals the molecular basis for human obesity-associated mutations. Structure-based design of leptin variants that destabilize the asymmetric LepR dimer yield both partial and biased agonists that partially suppress STAT3 activation in the presence of wild-type leptin and decouple activation of STAT3 from LepR negative regulators. Together, these results reveal the structural basis for LepR activation and provide insights into the differential plasticity of signaling pathways downstream of LepR.