Creation of a high cytotoxic active human tumor necrosis factor having the truncated and more basic amino terminus

In order to define the structure-functional relationship of tumor necrosis factor(TNF), a mutant TNF gene was created by site-specific mutagenesis based on the PCR technique. This gene was highly expressed in E.coli cells. The amount of the recombinant protein was up to about 80% of the total cellular proteins. Through one-step ion exchange chromatography, the mutant TNF could be purified to homogeneity. This mutein showed the molecular weight of a dimer but not a trimer. It bears the features of truncated amino terminus and increase of the basicity of amino terminal residues. Compared with the wild type TNF, the specific activity of mutant TNF was increased by fourfold.