IL-5R alpha EC

Interleukin‑5 Receptor alpha (IL‑5 R alpha), also known as CD125, is a 60 kDa hematopoietin receptor that plays a dominant role in eosinophil biology. Mature human IL‑5 R alpha consists of a 322 amino acid (aa) extracellular domain (ECD) with a WSxWS motif and a four-cysteine motif, a 20 aa transmembrane segment, and a 58 aa cytoplasmic domain. Within the ECD, human IL-5 R alpha shares 71% aa sequence identity with mouse and rat IL‑5 R alpha. Alternate splicing of human IL‑5 R alpha generates soluble secreted forms which function as IL‑5 antagonists. The high affinity receptor for IL‑5 is a complex that consists of the ligand binding IL‑5 R alpha and the transmembrane common beta chain (beta c/CD131) which is shared with the receptor complexes for IL‑3 and GM‑CSF. IL‑5 R alpha binds IL‑5 at low affinity and then associates with preformed beta c oligomers to form the signalling‑competent receptor complex.