Refolding and purification of yeast carboxypeptidase Y expressed as inclusion bodies in Escherichia coli

The genes encoding carboxypeptidase Y (CPY) and CPY propeptide (CPYPR) from Saccharomyces cerevisiae were cloned and expressed in Escherichia coli. Six consecutive histidine residues were fused to the C-terminus of the CPYPR for facilitated purification. High-level expression of CPY and CPYPR-His(6) was achieved but most of the expressed proteins were present in the form of inclusion bodies in the bacterial cytoplasm. The CPY and CPYPR-His(6) produced as inclusion bodies were separated from the cells and solubilized in 6 and 3 M guanidinium chloride, respectively. The denatured CPYPR-His(6) was refolded by dilution 1:30 into the renaturation buffer (50 mM Tris-HCl containing 0.5 M NaCl and 3 mM EDTA, pH 8.0), and the refolded CPYPR-His(6) was further purified to 90% purity by single-step immobilized metal ion affinity chromatography. The denatured CPY was refolded by dilution 1:60 into the renaturation buffer containing CPYPR-His(6) at various concentrations. Increasing the molar ratio of CPYPR-His(6) to CPY resulted in an increase in the CPY refolding yield, indicating that the CPYPR-His(6) plays a chaperone-like role in in vitro folding of CPY. The refolded CPY was purified to 92% purity by single-step p-aminobenzylsuccinic acid affinity chromatography. When refolding was carried out in the presence of 10 molar eq CPYPR-His(6), the specific activity, N-(2-furanacryloyl)-l-phenylalanyl-l-phenylalanine hydrolysis activity per milligram of protein, of purified recombinant CPY was found to be about 63% of that of native S. cerevisiae CPY.