Structure of the activation domain of the GM-CSF/IL-3/IL-5 receptor common beta-chain bound to an antagonist.
Heterodimeric cytokine receptors generally consist of a major cytokine-binding subunit and a signaling subunit. The latter can transduce signals by more than 1 cytokine, as exemplified by the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2 (IL-2), and IL-6 receptor systems. However, often the signaling subunits in isolation are unable to bind cytokines, a fact that has made it more difficult to obtain structural definition of their ligand-binding sites. This report details the crystal structure of the ligand-binding domain of the GM-CSF/IL-3/IL-5 receptor beta-chain (beta(c)) signaling subunit in complex with the Fab fragment of the antagonistic monoclonal antibody, BION-1. This is the first single antagonist of all 3 known eosinophil-producing cytokines, and it is therefore capable of regulating eosinophil-related diseases such as asthma. The structure reveals a fibronectin type III domain, and the antagonist-binding site involves major contributions from the loop between the B and C strands and overlaps the cytokine-binding site. Furthermore, tyrosine(421) (Tyr(421)), a key residue involved in receptor activation, lies in the neighboring loop between the F and G strands, although it is not immediately adjacent to the cytokine-binding residues in the B-C loop. Interestingly, functional experiments using receptors mutated across these loops demonstrate that they are cooperatively involved in full receptor activation. The experiments, however, reveal subtle differences between the B-C loop and Tyr(421), which is suggestive of distinct functional roles. The elucidation of the structure of the ligand-binding domain of beta(c) also suggests how different cytokines recognize a single receptor subunit, which may have implications for homologous receptor systems. (Blood. 2000;95:2491-2498)
Rossjohn
J
J
Ian Potter Foundation Protein Crystallography Laboratory, St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.
McKinstry
W J
WJ
Woodcock
J M
JM
McClure
B J
BJ
Hercus
T R
TR
Parker
M W
MW
Lopez
A F
AF
Bagley
C J
CJ
D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D002460:Cell Line; D018604:Epitope Mapping; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D018123:Receptors, Interleukin / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D016185:Receptors, Interleukin-3 / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D053649:Receptors, Interleukin-5
D000911:Antibodies, Monoclonal; D008024:Ligands; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D018123:Receptors, Interleukin; D016185:Receptors, Interleukin-3; D053649:Receptors, Interleukin-5