The Human Interferon Receptor:  NMR-Based Modeling, Mapping of the IFN-α2 Binding Site, and Observed Ligand-Induced Tightening^,

Abstract

The human interferon receptor (IFNAR) mediates the antiviral and antiproliferative activities of type I interferons (IFNs). This receptor is comprised of subunits IFNAR1 and IFNAR2, the latter exhibiting nanomolar affinity for IFNs. Here the extracellular domain of IFNAR2 (IFNAR2-EC), a soluble 25 kDa IFN-binding polypeptide, and its complex with IFN-alpha 2 were studied using multidimensional NMR. IFNAR2-EC is comprised of two fibronectin-III (FN-III) domains connected by a helical hinge region. The deduced global fold was utilized to improve the alignment of IFNAR2-EC against structurally related receptors and to model its structure. A striking feature of IFNAR2-EC is the limited and localized deviations in chemical shifts exhibited upon ligand binding, observed for only 15% of its backbone (1)H and (15)N nuclei. Analysis of these deviations maps the IFN-alpha 2 binding site upon IFNAR2-EC to a contiguous surface on the N-terminal domain, including the S3-S4 loop (residues 44-53), the S5-S6 loop and S6 beta-strand (residues 74-82), and the S7 beta-strand and the hinge region (residues 95-105). The C-terminal domain contributes only marginally to ligand binding, and no change in the hypothesized interdomain interface is observed. The proposed binding domain encompasses all residues implicated by mutagenesis studies in IFN binding, and suggests adjacent residues cooperate in forming the binding surface. D(2)O-exchange experiments indicate that binding of IFN-alpha2 induces tightening of the N-terminal domain of IFNAR2-EC. This increase in receptor rigidity may play an important role in initiating the intracellular stage of the IFN signaling cascade.

Respiratory virus induction of alpha‐, beta‐ and lambda‐interferons in bronchial epithelial cells and peripheral blood mononuclear cells

“…For both a-and b-IFNs it is likely that IFN proteins are quickly taken up by the IFN-ab receptor as the affinity of the IFN AR2 subunit for IFN-a2 alone is high (K D 3 nM) and increased up to 20-fold when complexed with IFN AR1 (33). The affinities of the IFN-k receptor subunits for the IFN-ks are not known and the assay for IFN-ks was considerably less sensitive (25 pg/ml) than those for type I IFNs (0.63 and 2.5 pg/ml for a and b, respectively), potentially explaining why the IFN-ks were not detectable despite mRNAs being induced to higher levels than the type I IFNs.…”

Interferon-α Promotes the Anti-Proliferative Effect of Gefitinib (ZD1839) on Human Colon Cancer Cell Lines

“…IFNα binds to cell membrane receptors, IFNαR1 and IFNαR2 [29], leading to activation of IFNα-associated Janus kinases (JAK), Jak1 and Tyk2. These are non-receptor tyrosine kinases that mediate cytokine-induced signal transduction [30].…”

Expression of Interferon Receptor Subunits, IFNAR1 and IFNAR2, in the Ovine Uterus1

“…Its long intracellular region of 268 amino acids [20] binds Jak1 and Stat2 [21][22][23][24][25] and possibly other signal transduction components [26]. Even though crystallographic data are still lacking, much is known about the structures of the receptors through modeling and other types of inference [27][28][29][30]. However, scant data exist on their expression patterns within various organs, possibly because it has been assumed that the receptors, much like the major histocompatibility complex, are ubiquitously expressed.…”