NMR Mapping of the IFNAR1-EC Binding Site on IFNα2 Reveals Allosteric Changes in the IFNAR2-EC Binding Site

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Abstract
All type I interferons (IFNs) bind to a common cell-surface receptor consisting of two subunits. IFNs initiate intracellular signal transduction cascades by simultaneous interaction with the extracellular domains of its receptor subunits, IFNAR1 and IFNAR2. In this study, we mapped the surface of IFNα2 interacting with the extracellular domain of IFNAR1 (IFNAR1-EC) by following changes in or the disappearance of the 1H−15N TROSY-HSQC cross peaks of IFNα2 caused by the binding of the extracellular domain of IFNAR1 (IFNAR1-EC) to the binary complex of IFNα2 with IFNAR2-EC. The NMR study of the 89 kDa complex was conducted at pH 8 and 308 K using an 800 MHz spectrometer. IFNAR1 binding affected a total of 47 of 165 IFNα2 residues contained in two large patches on the face of the protein opposing the binding site for IFNAR2 and in a third patch located on the face containing the IFNAR2 binding site. The first two patches form the IFNAR1 binding site, and one of these matches the IFNAR1 binding site previously identified by site-directed mutagenesis. The third patch partially matches the IFNα2 binding site for IFNAR2-EC, indicating allosteric communication between the binding sites for the two receptor subunits.