Brevibacillus choshinensis (formerly Bacillus brevis) is a protein-hyperproducing bacterium and has been used for commercial protein production. Here, we cloned thioredoxin (trxA) and thioredoxin reductase (trxB) genes from B. choshinensis, and expressed the gene products in Escherichia coli with an amino-terminal hexa-His-tag for purification and characterization. His-TrxA and His-TrxB were purified to homogeneity with one-step Ni-NTA affinity column chromatography, and the two recombinant proteins showed identical specific activity with or without removal of the amino-terminal His-tag, indicating that the extrasequence containing the hexa-His-tag did not affect their enzymatic activities. The E coli expression system used here resulted in a 40-fold increase in production of His-TrxB protein compared to the level of native TrxB produced in non-recombinant B. choshinensis cells. TrxA and TrxB proteins with carboxy-terminal His-tag (TrxA-His and TrxB-His) were successfully expressed in B. choshinensis and were purified by Ni-NTA column chromatography. Co-expression of TrxA-His with recombinant human epidermal growth factor (hEGF) in B. choshinensis promoted the extracellular production of hEGF by up to about 200%. (C) 2004 Elsevier Inc. All rights reserved.