In vitro refolding of carboxypeptidase T precursor from Thermoactinomyces vulgaris obtained in Escherichia coli as cytoplasmic inclusion bodies

Carboxypeptidase T precursor from Thermoactinomyces vulgaris, which fails to contain its own leader peptide, has been expressed in Escherichia coli as insoluble cytoplasmic inclusion bodies. The yield of a washed recombinant protein from 1 L of culture liquid was about 60 mg. The obtained inclusion bodies were denatured in 6 M guanidine-HCl and then renatured by a rapid dilution. The important role of calcium for the complete stabilization of the refolded carboxypeptidase T precursor was established. After removal of minor admixture proteins by gel-filtration through Superdex 75, an electrophoretically homogeneous preparation of the native precursor of carboxypeptidase T was obtained. Processing of the resulting protein by subtilisin led to the formation of the mature carboxypeptidase T in which N-terminal sequence, molecular size, thermal stability, and catalytic properties were comparable to those of the natural enzyme.