Structural insights into IL-11-mediated signalling and human IL6ST variant-associated immunodeficiency.

Area of Science:

• Structural Biology
• Immunology
• Molecular Cell Biology

Background:

• Interleukin-11 (IL-11) and Interleukin-6 (IL-6) are critical cytokines that activate cellular signaling pathways.
• These cytokines signal through the common receptor subunit gp130, a process involving receptor complex assembly.
• The precise mechanism of signal transmission across the cell membrane after receptor binding remains incompletely understood.

Purpose of the Study:

• To elucidate the structural basis of IL-11 and IL-6 receptor complex formation and signal transduction.
• To investigate how mutations in the gp130 receptor subunit affect signaling outcomes, particularly in the context of human immune deficiencies.
• To understand the role of gp130 receptor geometry in mediating downstream cellular responses.

Main Methods:

• Cryo-electron microscopy (cryoEM) was employed to determine the high-resolution structure of the IL-11 receptor recognition complex.
• CryoEM was also used to solve structures of IL-11 and IL-6 complexes with a disease-associated mutant form of gp130.
• Molecular dynamics (MD) simulations were performed to analyze the dynamic behavior of the wild-type and mutant gp130 complexes.

Main Results:

• The study determined the cryoEM structure of the IL-11 receptor recognition complex, highlighting differences in gp130-binding interfaces.
• Structures of IL-11 and IL-6 complexes with a disease-associated gp130 mutant revealed increased flexibility and altered extracellular domain distances.
• Molecular dynamics simulations indicated that these geometric changes are minimized at the transmembrane helix, suggesting a critical geometry for signaling.

Conclusions:

• Differences in gp130-binding interfaces contribute to distinct signaling outcomes for IL-11 and IL-6.
• Disease-associated mutations in gp130 can impair signaling by disrupting receptor complex dynamics and geometry, even without blocking cytokine binding.
• A stringent geometric requirement at the cell membrane, akin to a "dimer switch," is essential for initiating downstream signaling events.