One Target-Two Different Binding Modes: Structural Insights into Gevokizumab and Canakinumab Interactions to Interleukin-1β

Interleukin-1 beta (IL-1 beta) is a key orchestrator in inflammatory and several immune responses. IL-1 beta exerts its effects through interleukin-1 receptor type I (IL-1RI) and interleukin-1 receptor accessory protein (IL-1RAcP), which together form a heterotrimeric signaling-competent complex. Canakinumab and gevokizumab are highly specific IL-1 beta monoclonal antibodies. Canakinumab is known to neutralize IL-1 beta by competing for binding to IL-1R and therefore blocking signaling by the antigen:antibody complex. Gevokizumab is claimed to be a regulatory therapeutic antibody that modulates IL-1 beta bioactivity by reducing the affinity for its IL-1R1:IL-1RAcP signaling complex. How IL-1 beta signaling is affected by both canakinumab and gevokizumab was not yet experimentally determined. We have analyzed the crystal structures of canakinumab and gevokizumab antibody binding fragment (Fab) as well as of their binary complexes with IL-1 beta. Furthermore, we characterized the epitopes on IL-1 beta employed by the antibodies by NMR epitope mapping studies. The direct comparison of NMR and X-ray data shows that the epitope defined by the crystal structure encompasses predominantly those residues whose NMR resonances are severely perturbed upon complex formation. The antigen:Fab co-structures confirm the previously identified key contact residues on IL-1 beta and provide insight into the mechanisms leading to their distinct modulation of IL-1 beta signaling. A significant steric overlap of the binding interfaces of IL-1R and canakinumab on IL-1 beta causes competitive inhibition of the association of IL-1 beta and its receptor. In contrast, gevokizumab occupies an allosteric site on IL-1 beta and complex formation results in a minor reduction of binding affinity to IL-1RI. This suggests two different mechanisms of IL-1 beta pathway attenuation. (C) 2012 Elsevier Ltd. All rights reserved..