Expression, in Escherichia coli, of a soluble human tumor necrosis factor receptor

We have expressed in Escherichia coli a soluble, truncated form of the human 55 kDa Tumor Necrosis Factor (TNF) receptor. For this purpose a plasmid was constructed which contains the extracellular domain of the 55 kDa TNF receptor fused to the coding sequence of the IgG binding domains of protein A from Staphylococcus aureus. The fusion product (TNFR-PA) obtained in E. coli is a soluble protein which bound human TNF alpha (huTNF alpha) with high affinity. In ligand-blotting experiments huTNF alpha bound to a single 52 kDa protein, a molecular mass corresponding to that expected for the monomeric fusion product. In gel filtration experiments binding activity was recovered from fractions that eluted at a volume corresponding to 140-150 kDa. TNFR-PA neutralized huTNF alpha in an in vitro cytotoxicity assay.