The extracellular portions of the chains that comprise
the human type I interferon receptor, IFNAR1 and IFNAR2,
have been expressed and purified as recombinant soluble
His-tagged proteins, and their interactions with each other
and with human interferon-β-1a (IFN-β-1a) were
studied by gel filtration and by cross-linking. By gel
filtration, no stable binary complexes between IFN-β-1a
and IFNAR1, or between IFNAR1 and IFNAR2 were detected.
However, a stable binary complex formed between IFN-β-1a
and IFNAR2. Analysis of binary complex formation using
various molar excesses of IFN-β-1a and IFNAR2 indicated
that the complex had a 1:1 stoichiometry, and reducing
SDS-PAGE of the binary complex treated with the cross-linking
reagent dissucinimidyl glutarate (DSG) indicated that the
major cross-linked species had an apparent M>r
consistent with the sum of its two individual components.
Gel filtration of a mixture of IFNAR1 and the IFN-β-1a/IFNAR2
complex indicated that the three proteins formed a stable
ternary complex. Analysis of ternary complex formation
using various molar excesses of IFNAR1 and the IFN-β-1a/IFNAR2
complex indicated that the ternary complex had a 1:1:1
stoichiometry, and reducing SDS-PAGE of the ternary complex
treated with DSG indicated that the major cross-linked
species had an apparent Mr consistent
with the sum of its three individual components. We conclude
that the ternary complex forms by the sequential association
of IFN-β-1a with IFNAR2, followed by the association
of IFNAR1 with the preformed binary complex. The ability
to produce the IFN-β-1a/IFNAR2 and IFN-β-1a/IFNAR1/IFNAR2
complexes make them attractive candidates for X-ray crystallography
studies aimed at determining the molecular interactions
between IFN-β-1a and its receptor.