Computational modeling of the anti-inflammatory complexes of IL37

Interleukin (IL) 37 is an anti-inflammatory cytokine belonging to the IL1 protein family. Owing to its pivotal role in modulating immune responses, elucidating the IL37 complex structures holds substantial therapeutic promise for various autoimmune disorders and cancers. However, none of the structures of IL37 complexes have been experimentally characterized. This computational study aims to address this gap through molecular modeling and classical molecular dynamics simulations. We modeled all protein-protein complexes of IL37 using a range of methods from homology modeling to AlphaFold2 multimer predictions. Models that successfully recapitulated experimental features underwent further analysis through molecular dynamics simulations. As positive controls, binary and ternary complexes of IL18 from PDB were included for comparison. Several key findings emerged from the comparative analysis of IL37 and IL18 complexes. IL37 complexes exhibited higher mobility than the IL18 complexes. Simulations of the IL37-IL18Rα complex revealed altered receptor conformations capable of accommodating a dimeric IL37, with the N-terminal loop of IL37 contributing significantly to complex mobility. Additionally, the glycosyl chain on N297 of IL18Rα, which contours one edge of the cytokine binding surface, acted as a steric block against the N-terminal loop of IL37. Further, investigations into interactions between IL37 and IL18BP suggested that a binding mode homologous to IL18 was unstable for IL37, indicating an alternative binding mechanism. Altogether, this study accesses to the structure and dynamics of IL37 complexes, revealing the structural underpinnings of the IL37's modulatory effect on the IL18 signaling pathway.