A hot spot on interferon α/β receptor subunit 1 (IFNAR1) underpins its interaction with interferon-β and dictates signaling

Abstract

Edited by Luke O'NeillThe interaction of IFN-␤ with its receptor IFNAR1 (interferon ␣/␤ receptor subunit 1) is vital for host-protective anti-viral and anti-proliferative responses, but signaling via this interaction can be detrimental if dysregulated. Whereas it is established that IFNAR1 is an essential component of the IFNAR signaling complex, the key residues underpinning the IFN-␤-IFNAR1 interaction are unknown. Guided by the crystal structure of the IFN-␤-IFNAR1 complex, we used truncation variants and site-directed mutagenesis to investigate domains and residues enabling complexation of IFN-␤ to IFNAR1. We have identified an interface on IFNAR1-subdomain-3 that is differentially utilized by IFN-␤ and IFN-␣ for signal transduction. We used surface plasmon resonance and cell-based assays to investigate this important IFN-␤ binding interface that is centered on IFNAR1 residues Tyr 240 and Tyr The type I IFNs, including 14 IFN-␣ and lone IFN-␤, IFN-⑀, and IFN-, have critical roles in response to viral and bacterial infections and cancers (1, 2). They are also applied clinically for the treatment of hepatitis virus B and C (1), cancers including melanoma (3), and multiple sclerosis (4). Although they show clinical efficacy, their use is restricted by dose-limiting toxicities, including leukopenia, nausea, fatigue, neurological disorders (3), and localized cutaneous effects (5). All type I IFNs engage their cognate receptors, IFNAR1 and IFNAR2, to activate the canonical JAK-STAT signaling pathway, but ligand engagement can also activate alternative signaling pathways (6). Despite sharing these receptor components, there are IFN subtype-specific elements to signaling; compared with IFN-␣, IFN-␤ has specific roles in osteoclastogenesis (7), control of chronic viral infection (8), the potent induction of apoptotic pathways required for control of tumor cell growth, and the development of B cells and myelopoiesis (9).Structural insight into the IFN-IFNAR 5 interactions has been gleaned from the crystal structures of a human IFN-␣2 variant and human IFN-in complex with both IFNAR1 and IFNAR2 (10). Furthermore, specific insight into the mode of IFN-␤-mediated activation of IFNAR1 was obtained from the crystal structure of the murine IFN-␤-IFNAR1 complex (11). Comparison of these structures and evidence from the literature (12) suggests that the minimal ligand binding domains for human and mouse IFNAR1 are similar and sit broadly across the three membrane distal SDs (SD1-3) of the receptor with limited involvement of the membrane proximal subdomain, SD4 (Fig. 1A). It has also been shown that key residues discriminate between ligands and that there is potential for ligand-specific interaction interfaces (10, 11).

Defining the distinct, intrinsic properties of the novel type I interferon, IFNϵ

“…This analysis unexpectedly demonstrated that IFNε bound IFNAR1-ECD with higher affinity than IFNAR2-ECD, different from data reported for the IFNα which have a higher affinity for IFNAR2 (29). As expected, the affinity of the mIFNβ-IFNAR1 interaction as measured by MST was consistent with our previous report using surface plasmon resonance (32). Notably, the affinity of the mIFNβ-IFNAR1 interaction was higher than that observed for the human IFNβ-IFNAR1interaction (29).…”

Structural integrity with functional plasticity: what type I IFN receptor polymorphisms reveal

“…The interface on IFNAR1‐SD4 may be specific to IFNβ or specific to the murine system, because a comparable crystal structure with human IFNβ is yet to be determined. The majority contacts with IFNAR1 SD1‐3 is consistent with biochemical analyses that show this region is sufficient for in vitro ligand binding whereas SD4 is dispensable 21,60,98,99 (Fig. 2).…”

“…2). On SD3, two prominent residues, Tyr240 AR1 (the homologous Phe238 in human IFNAR1 is also a “hot‐spot” residue in the interface with IFNα and IFNω) and the unique Tyr274 AR1 form a “hot‐spot” of interaction in the IFNAR1‐IFNβ interface; these residues are also important in determining the magnitude of the signaling response and biologic activities exhibited by IFNβ 99 . Residues that make minor contributions to the ligand interface are also found on other regions of SD1‐3 AR1 (Fig.…”

“…Notwithstanding these differences, common sites for recognition or potential “anchor points” are present for IFNAR1 SD1‐3 that are conserved across species 21,48 . Interestingly, Tyr274 AR1 located in the mIFNAR1‐IFNβ interface on SD3 AR1 is important for formation of this high affinity interaction and mIFNβ‐mediated signals 99 . Because this residue is not conserved across species, and the residue with which it structurally aligns (Gln272 AR1 ) was not identified in the hIFNAR1‐hIFN interfaces, 48 Tyr274 AR1 may be an IFNβ‐specific anchor point on IFNAR1 or it may contribute to the species specificity exhibited by most IFNs.…”

“…2). This protein would likely possess the ligand binding “hot‐spot” residues on SD1 (Tyr70) however it would lack the “hot‐spot” and ligand‐specific residues on SD3 that make significant contributions to the strength of the IFNAR1‐ligand binding interface (including Phe238) 48,99 . This truncated form of IFNAR1 may therefore be unable to form a stable interaction with any ligand.…”