X-RAY STRUCTURE OF INTERLEUKIN-1 RECEPTOR ANTAGONIST AT 2.0-ANGSTROM RESOLUTION

Interleukin-1 receptor antagonist (IL-1ra) is a natural competitive an tagonist of IL-1. In order to further elucidate the mechanism by which IL-1ra binds without activating the IL-1 receptor, we have solved the crystal structure of IL-1ra at 2.0-Angstrom resolution. IL-1ra has th e same overall beta-trefoil fold as IL-1 alpha and IL-1 beta and has a very similar hydrophobic core. However, there are a number of structu ral differences between the molecules, including significant differenc es at the open end of the beta-barrel, which has been identified in IL -1 beta as a receptor binding site.