An expression system for secretion and purification of a genetically engineered thermostable chimera of protein A and alkaline phosphatase.

A chimera between gene segments of Protein A and a mutated alkaline phosphatase (lysine328 mutated to alanine) of Escherichia coli has been constructed. This chimeric gene was cloned in a T7 promoter-based IPTG-inducible expression vector. The chimeric protein was expressed in E. coli and was efficiently secreted into the periplasm, from which it could be easily purified by a combination of ion-exchange and gel permeation chromatography. The purified chimera was found to be thermostable and exhibited both IgG binding and high alkaline phosphatase activity. It was used as a probe in enzyme-linked immunosorbent assays and results indicate that it is a promising substitute for secondary antibodies in enzyme-linked immunoassays.