Cryo-EM structure of the interleukin-31 receptor complex defines non-canonical interactions that confer receptor specificity.

Interleukin-31 (IL-31) is a Th2-associated cytokine that induces inflammatory and pruritic diseases through a heterodimeric receptor composed of IL-31Rα and OSMRβ. Although IL-31 has emerged as an important therapeutic target, the molecular mechanism by which IL-31 engages IL-31Rα and OSMRβ to assemble its receptor complex remains poorly defined. Here we report a 3.3 Å cryo-EM structure of the human IL-31/IL-31Rα/OSMRβ complex. The structure reveals that IL-31 assembles its receptors through a site 2-site 3 architecture reminiscent of LIF and OSM, yet employs distinct receptor-recognition features at both interfaces. Site 2 is dominated by a hydrophilic IL-31-IL-31Rα interface that lacks the aromatic anchoring mode observed in LIF and OSM receptor complexes, whereas site 3 adopts a remodeled anchoring mode involving IL-31 K134, T130, and the conserved OSMRβ W267 anchor. Structure-guided mutagenesis and SPR binding analyses support the contributions of site 2 and site 3 interface residues to receptor recognition. Together, these findings reveal how non-canonical interactions at sites 2 and 3 confer receptor specificity within the IL-31 receptor complex.