Identification of Three Distinct Receptor Binding Sites of Murine Interleukin-11

Abstract

Interleukin-11 (IL-11) is a member of the gp130 family of cytokines. These cytokines drive the assembly of multisubunit receptor complexes, all of which contain at least one molecule of the transmembrane signaling receptor gp130. A complex of IL-11 and the IL-11 receptor (IL-11R) has been shown to interact with gp130, with high affinity, and to induce gp130-dependent signaling. In this study, we have identified residues crucial for the binding of murine IL-11 (mIL-11) to both the IL-11R and gp130 by examining the activities of mIL-11 mutants in receptor binding and cell proliferation assays. The location of these residues, as predicted from structural studies and a model of IL-11, reveals that mIL-11 has three distinct receptor binding sites. These are structurally and functionally analogous to the previously defined receptor binding sites I, II, and III of interleukin-6 (IL-6). This supports the hypothesis that IL-11 signals via the formation of a hexameric receptor complex and indicates that site III is a generic feature of cytokines that signal via association with gp130.

Multiple and highly divergent IL-11 genes in teleost fish

“…Most of the residues that are critical [the arginine (R) residue in helix D] or important for receptor binding are conserved or conservatively substituted. The same is true for the tryptophan (W) in the CD loop, that although dispensable for receptor binding, is essential for receptor activation (Barton et al 1999). This tryptophan is conserved in cyprinid IL-11a and IL-11b peptides and is substituted for a likewise aromatic phenylalanine (F) in the other fish sequences.…”

“…Asterisks indicate a significant difference (p<0.05) from the control group. Error bars indicate the standard deviation of four to five replicate samples its receptor complex in mammalian species (Barton et al 1999) are conserved in fish IL-11a and IL-11b peptides. Most of the residues that are critical [the arginine (R) residue in helix D] or important for receptor binding are conserved or conservatively substituted.…”

“…As bony fish IL-11a and IL-11b paralogues share relatively low amino acid identity with each other and with mammalian IL-11, only a few amino acid residues are identical throughout the alignment, although identities within the blocks of fish IL11a, fish IL-11b, and mammalian IL-11 are markedly higher. Carp IL-11 contains a conserved arginine (corresponding to human R190) in helix D and a tryptophane (corresponding to human W168) in the CD loop that were identified as crucial for receptor binding and signaling, respectively, in mouse (Barton et al 1999). The authors also identified four leucine residues (corresponding to L85, L88, L193, and L194) that are important for the binding of IL-11 to its receptor complex.…”

Leukemia Inhibitory Factor (LIF), Cardiotrophin-1, and Oncostatin M Share Structural Binding Determinants in the Immunoglobulin-like Domain of LIF Receptor

“…CNTF, CLC, IL-6, and IL-11) binds to this co-receptor (CNTFR, IL-6R, and IL-11R) through binding site I (C-terminal parts of the AB loop and of helix D (8,20,26,(33)(34)(35)(36)). The glycoprotein gp130 interacts through binding site II, located on the solvent-exposed faces of helices A and C (3,37,38).…”

Two Different Epitopes of the Signal Transducer gp130 Sequentially Cooperate on IL-6-Induced Receptor Activation

“…Similarly positioned receptor-engaging epitopes have been described for the closely related cytokines IL-11 (31,32) and CNTF (33), which signal via gp130/gp130 homodimers and gp130/LIFR heterodimers, respectively. The initial event in the formation of a signal transducing IL-6/IL-6R/gp130 ternary complex on the cell surface is the contact of site I of IL-6 with IL-6R, which is a prerequisite for the engagement of gp130 because neither IL-6 nor IL-6R alone have a detectable affinity for gp130.…”