One Target—Two Different Binding Modes: Structural Insights into Gevokizumab and Canakinumab Interactions to Interleukin-1β
Interleukin-1Î² (IL-1Î²) is a key orchestrator in inflammatory and several immune responses. IL-1Î² 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-1Î² monoclonal antibodies. Canakinumab is known to neutralize IL-1Î² 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-1Î² bioactivity by reducing the affinity for its IL-1RI:IL-1RAcP signaling complex. How IL-1Î² 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-1Î². Furthermore, we characterized the epitopes on IL-1Î² 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-1Î² and provide insight into the mechanisms leading to their distinct modulation of IL-1Î² signaling. A significant steric overlap of the binding interfaces of IL-1R and canakinumab on IL-1Î² causes competitive inhibition of the association of IL-1Î² and its receptor. In contrast, gevokizumab occupies an allosteric site on IL-1Î² and complex formation results in a minor reduction of binding affinity to IL-1RI. This suggests two different mechanisms of IL-1Î² pathway attenuation. âº Crystallographic analysis of two co-crystal structures of anti-IL-1Î² Fab with IL-1Î². âº Canakinumab and gevokizumab exert two distinct modes of actions in IL-1Î² signaling. âº Canakinumab neutralizes IL-1Î² by competing for binding to IL-1R. âº Gevokizumab functions by a noncompetitive, allosteric mechanism. âº Direct comparison of X-ray- and NMR-derived epitopes revealed high consistency.