Structural studies of the IFNλ4 receptor complex using cryoEM enabled by protein engineering

Area of Science:

• Immunology
• Structural Biology
• Virology

Background:

• Interferon lambda 4 (IFNλ4) discovery in 2013 linked to viral clearance issues.
• Previous structural and functional studies limited by difficulties in protein production.
• Understanding IFNλ4's paradoxical behavior requires detailed structural and functional characterization.

Purpose of the Study:

• To develop a method for robust production of IFNλ4.
• To determine the high-resolution structures of IFNλ4 and IFNλ3 in complex with their receptors.
• To elucidate the structural basis for differences in receptor engagement and signaling.

Main Methods:

• Robust production of IFNλ4 protein.
• Yeast surface display for affinity maturation of IL10Rβ.
• Cryogenic electron microscopy (cryo-EM) to solve structures of IFNλ4/IFNλR1/IL10Rβ and IFNλ3/IFNλR1/IL10Rβ complexes.
• Molecular modeling and simulation for structural analysis.

Main Results:

• Successfully produced and purified IFNλ4 protein.
• Determined 72 kDa structures of IFNλ4 and IFNλ3 bound to their receptors (IFNλR1 and IL10Rβ) at 3.26 Å and 3.00 Å resolution, respectively.
• Identified distinct receptor engagement and a 12-degree rotation in receptor geometry between IFNλ4 and IFNλ3 complexes.
• Discovered a unique region in IFNλ4 that, upon modification, enables protein secretion.

Conclusions:

• The study provides the first structural and functional insights into IFNλ4.
• Structural differences explain variations in cell signaling, gene induction, and antiviral activities.
• Findings pave the way for understanding and potentially correcting IFNλ4 dysfunction.