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

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 IFN alpha 2 interacting with the extracellular domain of IFNAR1 (IFNAR1-EC) by following changes in or the disappearance of the H-1-N-15 TROSY-HSQC cross peaks of IFN alpha 2 caused by the binding of the extracellular domain of IFNAR1 (IFNAR1-EC) to the binary complex of IFN alpha 2 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 IFN alpha 2 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 IFN alpha 2 binding site for IFNAR2-EC, indicating allosteric communication between the binding sites for the two receptor subunits.