Mapping Receptor Binding Sites in Interleukin (IL)-1 Receptor Antagonist and IL-1β by Site-directed Mutagenesis

• Published in: The Journal of biological chemistry Vol. 270; no. 19; pp. 11477 - 11483
• Main Authors: Evans, Ron J., Bray, Jeff, Childs, John D., Vigers, Guy P.A., Brandhuber, Barbara J., Skalicky, Jack J., Thompson, Robert C., Eisenberg, Stephen P.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 12.05.1995
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.19.11477

Interleukin-1 receptor antagonist (IL-1ra), an IL-1 family member, binds with high affinity to the type I IL-1 receptor (IL-1RI), blocking IL-1 binding but not inducing an IL-1-like response. Extensive site-directed mutagenesis has been used to identify residues in IL-1ra and IL-1β involved in binding to IL-1RI. These analyses have revealed the presence of two discrete receptor binding sites on IL-1β. Only one of these sites is present on IL-1ra, consisting of residues Trp-16, Gln-20, Tyr-34, Gln-36, and Tyr-147. Interestingly, the absent second site is at the location of the major structural difference between IL-1ra and IL-1β, which are otherwise structurally similar. The two receptor binding sites on IL-1β are also present on IL-1α. Thus, it appears that the two IL-1 agonist molecules have two sites for IL-1RI binding, and the homologous antagonist molecule, IL-1ra, has only one. Based on these observations, a hypothesis is presented to account for the difference in activity between the agonist and antagonist proteins. It is proposed that the presence of the two receptor binding sites may be necessary for agonist activity.