Overexpression of the soluble form of chicken cystatin in Escherichia coliand its purification

A cDNA encoding chicken cystatin was cloned into the pET-23a(+) expression vector and then transformed into Escherichia coli AD494(DE3)pLysS expressio n host. An active soluble form of cystatin was expressed in the cytoplasm o f E. coli induced by isopropyl beta-D-thiogalactopyranoside. The recombinan t chicken cystatin was purified to electrophoretic homogeneity by a simple and rapid method involving heat treatment and Sephacryl S-100 gel filtratio n chromatography. The recombinant cystatin behaved as a thermal-stable prot ein and exhibited papain-like protease inhibition activity comparable to th e natural chicken cystatin.