ISOLATION OF A BIOLOGICALLY-ACTIVE SOLUBLE HUMAN INTERFERON-ALPHA RECEPTOR-GST FUSION PROTEIN EXPRESSED IN ESCHERICHIA-COLI

The cDNA encoding the extracellular domain of the human interferon-alp ha (IFN-alpha) receptor (Uze, G., Lutfalla, G., and Gresser, I. Cell 1 990;60:225-234) lacking the signal peptide has been expressed in Esche richia coli as a fusion protein with glutathione S-transferase, The fu sion protein represented 12% of total bacterial proteins and was found exclusively within cytoplasmic inclusion bodies, Inclusion body mater ial was completely solubilized by 8 M urea; 20% solubilization was ach ieved by cell lysis in the presence of 0.45% cholamidopropyl dimethyla mmoniol-propane sulfonate and 1% Triton X-100, The soluble fusion prot ein was purified by gel filtration and affinity chromatography, Overal l recovery of affinity purified fusion protein was approximately 100-2 00 mu g/liter of cell culture, The affinity purified and refolded fusi on protein exhibited the expected amino terminal sequence and M(r) of 68,000 on reduced sodium dodecylsulfate gel electrophoresis, The prote in reacted with antibodies specific for the cloned IFN-alpha receptor and inhibited the antiviral and antiproliferative activities of recomb inant IFN-alpha B. We have demonstrated that the fusion protein binds to IFN-alpha B and competes with the cell surface receptor for binding to this IFN-alpha species.