Mutational and structural analysis of the binding interface between type I interferons and their receptor Ifnar2

Area of Science:

• Immunology
• Biophysics
• Molecular Biology

Background:

• Type I interferons (IFN) mediate crucial immune responses by binding to cell surface receptors ifnar1 and ifnar2.
• Understanding the biophysical basis of IFN-receptor interactions is vital for elucidating IFN signaling pathways.

Purpose of the Study:

• To characterize the functional epitopes and biophysical interactions between IFNalpha2 and the extracellular domain of ifnar2 (ifnar2-EC).
• To investigate the impact of specific mutations on binding affinity, thermodynamic parameters, and antiviral potency.

Main Methods:

• Utilized a mutational study on purified recombinant IFNalpha2 and ifnar2-EC proteins.
• Employed label-free heterogeneous phase detection to determine kinetic and thermodynamic parameters.
• Correlated anti-viral potency of mutants with binding affinity to ifnar2.

Main Results:

• Identified a small functional epitope on IFNalpha2, with residues L30 and R33 as critical hot-spots contributing significantly to interaction energy.
• Localized hot-spot residues (T46, I47, M48) and other key residues on ifnar2 involved in IFNalpha2 binding.
• Established a proportional correlation between binding affinity and anti-viral potency, suggesting receptor binding is rate-limiting for IFN signaling.
• Revealed distinct binding centers for IFNalpha2 and IFNbeta on ifnar2, despite competitive binding, potentially influencing signaling orientation.

Conclusions:

• Detailed mapping of functional epitopes on IFNalpha2 and ifnar2 provides insights into the molecular basis of Type I IFN signaling.
• The identified hot-spot residues are crucial for high-affinity binding and subsequent antiviral activity.
• Differential binding modes of IFNalpha2 and IFNbeta suggest a mechanism for distinct signaling outcomes.