The Thioredoxin Reductase-deficient E.coli Mutant Enhances Expression into Solution of Recombinant Proteins Containing Cys Residues.

A 3D artificial protein, a salmon calcitonin hexa-polymer, a salmon calcitonin octo-polymer and a human prourokinase, was expressed in the cytoplasma of E.coli GJ980(trxB(-)) mutant. These recombinant proteins containedcysteine residues of different length ranging from 12-22 residues. The mutation was mapped to the gene for thioredoxin reductase(trxB) and was found to eliminate the activity of this enzyme, which was thought to contribute to the sulfhydryl reducing potential of the cytoplasm. Recombinant salmon calcitonin hexapolymer, salmon calcitonin octo-polymer and human prourokinase had more soluble form in cytoplasm of GJ980 mutants than in wild-type strain, while 3D-protein, which has nocysteine residue, still remain in insoluble form. Results indicate the GJ980(trxB(-)) strain allowed the formation of disulphide bonds in the cell cytoplasm which is believed to encourage correct folding and soluble expression of the recombinant proteins.