High-level Expression and Purification of Recombinant 4-Aminobutyrate Aminotransferases in Escherichia coli

The protein coding sequence of the 4-aminobutyrate aminotransferase was amplified by polymerase chain reaction (PCR) from a previously cloned cDNA of pig brain using a pair of primers based on the published sequence. The amplified DNA was introduced into a T7 expression vector. Recombinant 4-aminobutyrate aminotransferases were overexpressed in Escherichia coli. The inclusion bodies were formed when enzyme was overexpressed. The unfolded, overproduced proteins were purified by chromatography with hydroxyapatite and refolded by a sequential dialysis method. The renatured 4-aminobutyrate aminotransferase regained the catalytic activity. However, the purified mutant protein did not show the catalytic function of 4-aminobutyrate aminotransferase.