Distinct structural requirements for interleukin-4 (IL-4) and IL-13 binding to the shared IL-13 receptor facilitate cellular tuning of cytokine responsiveness.
Both interleukin-4 (IL-4) and IL-13 can bind to the shared receptor composed of the IL-4 receptor alpha chain and the IL-13 receptor alpha1 chain (IL-13Ralpha1); however, the mechanisms by which these ligands bind to the receptor chains are different, enabling the principal functions of these ligands to be different. We have previously shown that the N-terminal Ig-like domain in IL-13Ralpha1, called the D1 domain, is the specific and critical binding unit for IL-13. However, it has still remained obscure which amino acid has specific binding capacity to IL-13 and why the D1 domain acts as the binding site for IL-13, but not IL-4. To address these questions, in this study we performed mutational analyses for the D1 domain, combining the structural data to identify the amino acids critical for binding to IL-13. Mutations of Lys-76, Lys-77, or Ile-78 in c' strand in which the crystal structure showed interaction with IL-13, and those of Trp-65 and Ala-79 adjacent to the interacting site, resulted in significant impairment of IL-13 binding, demonstrating that these amino acids generate the binding site. Furthermore, mutations of Val-35, Leu-38, or Val-42 at the N-terminal beta-strand also resulted in loss of IL-13 binding, probably from decreased structural stability. None of the mutations employed here affected IL-4 binding. These results demonstrate that the D1 domain of IL-13Ralpha1 acts as an affinity converter, through direct cytokine interactions, that allows the shared receptor to respond differentially to IL-4 and IL-13.
Ito
Takachika
T
Division of Medical Biochemistry, Department of Biomolecular Sciences, Saga Medical School, Saga, Japan.
Suzuki
Shoichi
S
Kanaji
Sachiko
S
Shiraishi
Hiroshi
H
Ohta
Shoichiro
S
Arima
Kazuhiko
K
Tanaka
Go
G
Tamada
Taro
T
Honjo
Eijiro
E
Garcia
K Christopher
KC
Kuroki
Ryota
R
Izuhara
Kenji
K
D002460:Cell Line; D006801:Humans; D018793:Interleukin-13 / Q000235:genetics / Q000378:metabolism*; D053661:Interleukin-13 Receptor alpha1 Subunit; D015847:Interleukin-4 / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D009154:Mutation; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D013329:Structure-Activity Relationship
C508181:IL13RA1 protein, human; C508598:IL4 protein, human; D018793:Interleukin-13; D053661:Interleukin-13 Receptor alpha1 Subunit; D008024:Ligands; D015847:Interleukin-4