Structures of the interleukin 11 signalling complex reveal dynamics of gp130 extracellular domains and the inhibitory mechanism of a cytokine variant

Abstract

Interleukin (IL-)11, an IL-6 family cytokine, has pivotal roles in numerous autoimmune diseases, fibrotic complications, and solid cancers. Despite intense therapeutic targeting efforts, structural understanding of IL-11 signalling and mechanistic insights into current inhibitors is lacking. Here we present cryo-EM and crystal structures of the IL-11 signalling complex, including the complex containing the complete extracellular domains of the shared IL-6 family β-receptor, gp130. We show that the membrane-proximal domains of gp130 are dynamic and do not participate in complex assembly. We demonstrate that the cytokine mutant 'IL-11 Mutein' competitively inhibits signalling in human cell lines. Structural shifts in IL-11 Mutein underlie inhibitory activity by altering cytokine binding interactions at all three receptor-engaging sites and abrogating the final gp130 binding step. Our results reveal the structural basis of IL-11 signalling, define the molecular mechanisms of an inhibitor, and advance understanding of gp130-containing receptor complexes, with potential applications in therapeutic development.

Structural insights into the assembly of gp130 family cytokine signaling complexes

“…The two gp130 juxtamembrane D6 domains in our IL-6 signaling complex are better resolved, presumably because the insertion of TM helices into the detergent micelle has restrained the flexibility of these domains. Consistent with the observation that no D6-D6 contacts are made in the gp130 crystal lattice (2), we do not see direct interactions between the gp130 juxtamembrane domains in the IL-6 signaling complex, which may explain why the presence of gp130 D4 to D6 did not increase gp130 binding affinity to IL-6 or IL-11 (13,27). In contrast, in the VEGF-A/VEGFR-1 complex, the presence of VEGFR-1 membrane-proximal D4 to D7 led to 20 times higher binding affinity of VEGFR-1 to the ligand (41).…”

“…The overall architecture of the IL-6 signaling complex is very similar to that of the IL-11 signaling complex ( 27 ). The assembly of the IL-6 complex interaction core region agrees with the 3.65-Å crystal structure of gp130 D1 to D3/IL-6Rα D2D3/IL-6 complex ( 3 ).…”

“…Site 3a has a relatively limited buried surface area (962 Å 2 ) with W197 at the N terminus of p28 helix D packing against gp130 Y116 to serve as a binding anchor. The aromatic residue W197, which is equivalent to a phenylalanine residue in the F XX K motif of CNTF (F152), CLCF1 (F178), and LIF (F178), is evolutionarily conserved in IL-6 (W185) ( 3 ), vIL-6 (W166) ( 24 ), and IL-11 (W168) ( 27 ) and has been shown to be crucial for IL-27 signaling ( 26 ). A group of residues at the N terminus of the p28 AB loop (V76, L80, and L81) make additional hydrophobic contacts with gp130 D1.…”

“…We further compared the structures of four nonsignaling receptors, including CNTFRα, IL-6Rα, and EBI3 characterized in our study, as well as IL-11Rα, which has been well studied by the Griffin group ( 27 , 29 ). No dramatic conformational changes of CNTFRα and IL-6Rα were observed upon ligand binding (Fig.…”

“…We next compared seven gp130 family cytokines, including five characterized in this study, as well as OSM and IL-11, which are both well characterized structurally (27)(28)(29)(30). Despite the low sequence identities of these cytokines (table S1), they all share a canonical four-helix bundle structure, where four major helices are linked by three loops (Fig.…”