Scientific Publications by FDA Staff

J Interferon Cytokine Res 2019 May;39(5):283-92

S27 of IFNalpha1 contributes to its low affinity for IFNAR2 and weak antiviral activity.

Sharma N, O'Neal AJ, Gonzalez C, Wittling M, Gjinaj E, Parsons LM, Panda D, Khalenkov A, Scott D, Misra S, Rabin RL

Type I interferons (IFNs) signal by forming a high affinity IFN-IFNAR2 dimer, which subsequently recruits IFNAR1 to form a ternary complex that initiates JAK/STAT signaling. Among the 12 IFNalpha subtypes, IFNalpha1 has a uniquely low affinity for IFNAR2 (<100 x of the other IFNalpha subtypes) and commensurately weak antiviral activity, suggesting an undefined function distinct from suppression of viral infections. Also unique in IFNalpha1 is substitution of a serine for phenylalanine at position 27, a contact point that stabilizes the IFNalpha:IFNAR2 hydrophobic interface. To determine whether IFNalpha1-S27 contributes to the low affinity for IFNAR2, we created an IFNalpha1 mutein, IFNalpha1-S27F, and compared it to wild-type IFNalpha1 and IFNalpha2. Substitution of phenylalanine for serine increased affinity for IFNAR2 approximately 4-fold and commensurately enhanced activation of STAT1, STAT3, and STAT5, transcription of a subset of interferon stimulated genes, and restriction of vesicular stomatitis virus infection in vitro. Structural modeling suggests that S27 of IFNalpha1 disrupts the IFNalpha:IFNAR2 hydrophobic interface that is otherwise stabilized by F27 and that replacing S27 with phenylalanine partially restores the hydrophobic surface. Disruption of the hydrophobic IFNalpha:IFNAR2 interface by the unique S27 of IFN alpha1 contributes to its low affinity and weak antiviral activity.