Structural insights into the assembly of gp130 family cytokine signaling complexes

Abstract

The gp130 family cytokine signaling complexes have limited structural information despite their crucial roles in various cellular processes. We determined cryo-EM structures of several complexes of this family, containing full ectodomains of both signaling receptors bound to their respective ligands CNTF, CLCF1, LIF, IL-27, and IL-6. Our structures reveal that gp130 serves as a central receptor by engaging Site 2 of CNTF, CLCF1, LIF, and IL-6, and Site 3 of IL-27 and IL-6. The acute bends at both signaling receptors in all complexes bring the membrane-proximal domains to a ~30 Å range but with distinct distances and orientations, which might determine biological specificities of these cytokines. We also reveal how CLCF1 engages its secretion chaperone CRLF1. Our data provide valuable insights for therapeutically targeting gp130-mediated signaling.

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

“…The structures bear a striking resemblance to a table, with D2 of IL-11Rα and gp130, and IL-11 forming the ‘table-top’, and D3 of IL-11Rα and gp130 forming the ‘legs’ (Figure 1Aii), similar to the IL-6 36 and vIL-6 35 complexes. The density for the gp130 EC complex shows that D5-D6 of the two gp130 molecules ‘cross over’ (Figure 1Bii), as previously suggested by low-resolution EM reconstructions of the complete extracellular domains of the IL-6 49,50 and IL-11 48 signalling complexes, and recent cryoEM studies of the IL-6 signalling complex 51 .…”

“…Notably, the new position of the AB loop is stabilised by several new intra-IL-11 contacts, including a hydrogen bond formed by the δ-sulfur of M59 and the indole nitrogen of W166, and two hydrogen bonds formed by the guanidinium guanidium group of R75 with backbone atoms of T56 and A58 in the AB loop (Figure 2Ciii). These conformational changes of IL-11 upon binding IL-11Rα are significantly larger than those observed for other IL-6 family members, IL-6 and LIF 36,38,51 . Several additional contacts are formed by the N-terminal end of the AB loop, including a salt bridge between D48 on the cytokine and K129 on IL-11Rα (Figure 2Dii).…”

“…Thus, the 58 PAIDY 62 mutations alter the position of the AB-loop, shifting the register of key loop-core interactions by three residues, while maintaining the composition of the interacting residues. This register change is due to a shift of the ‘LX(S/T)LP’ motif that mediates loop-core contacts: In IL-11 Δ10 and IL-11 Δ10/W147A the motif is 51 LDSLP 55 , while in IL-11 Δ10/Mutein the interacting motif is 54 LPTLP 58 . The result is that the bulk of the loop is shifted toward site-III and the N-terminal turn of helix-B is unfolded.…”

Mechanism of receptor assembly via the pleiotropic adipokine Leptin

“…By contrast, all other ‘tall’ gp130-class cytokine receptors feature ectodomain stalks with three FnIII domains, where the additional membrane-proximal domain (with respect to LEP-1. R) could possibly pack vertically as suggested from observed homo- or heteromeric 2:2 complexes of such cytokine receptors 26 .…”

Human interleukin-12α and EBI3 are cytokines with anti-inflammatory functions

“…In strong contrast to the detailed insights into its many biological functions stands our limited understanding of the structure and receptor repertoire of IL-35. For IL-12, IL-23, and IL-27, experimental structures and experimentally validated models of the isolated cytokines (19)(20)(21)(22) and their receptor binding are available (23)(24)(25)(26)(27)(28). In case of IL-35, however, even comprehensive studies have failed to identify its heterodimerization interface (29), which thus appears to be distinct from the other family members.…”