Overexpression and refolding of thioredoxin/TRAIL fusion from inclusion bodies and further purification of TRAIL after cleavage by enteropeptidase

The human TRAIL gene (encoding residues 114–281) was synthesized by PCR and cloned into plasmid pET-32a. High level expression (1.5 g l−1) of thioredoxin/TRAIL fusion was achieved in Escherichia coli strain BL21(DE3), mainly as inclusion bodies. Refolded fusion thioredoxin/TRAIL was cleaved by enteropeptidase and TRAIL was separated from thioredoxin on Ni-NTA agarose. High yield (400 mg l−1) of TRAIL without N-terminal methionine and His tag was obtained. Sedimentation coefficient demonstrated that 98% of TRAIL formed trimers. TRAIL formed crystals of space group P3 1 with unit-cell dimensions a = b = 72.5 A, c = 141.5 A. Apoptosis induced in HeLa cells by purified TRAIL was 5-fold enhanced by emetine.