Recombinant DNA technology allows the addition of short pieces of well-defined tags, "peptides" or proteins at the amino or c-terminus of target genes, which can provide 'affinity handles' designed to bind specific matrices. Therefore, tags enable a selective identification and purification of the protein of interest. Eukaryotic genes are often cloned into E. coli thioredoxin gene, resulting in the expression of a desired protein as a fusion hybrid with thioredoxin (1). Thioredoxin is a small electron transport protein that serves as hydrogen door in the enzymatic reduction of ribonucleotides to deoxyribonucleotides (1). Thioredoxin from E. coli consists of a single polypeptide of 108 aa (~11.7kD). The gene encoding Thioredoxin has been clones into several plasmids and serves as a fusion partner for the expression of other clones genes. The system often produces high expression of soluble fusion proteins in the E. coli cytoplasm. The fusion proteins may also fold correctly with biological activity.
Anti-Thioredoxin antibodies allow a simple isolation of fusion proteins directly from the crude bacterial lysate, using immunoaffinity chromatography (1) or used in immunoprecipitation. Anti- thioredoxin can also be used for the immunocytochemical detection of thioredoxin in cells and tissues that express transfected bacterial thioredoxin gene (1). Ant-thioredoxin may be used in various immunoassays to identify the expression of thioredoxin fusion protein.
