Trx, also known as TrxA or Thioredoxin, is a 12-kDa soluble, thermostable protein from E. coli. The Trx tag is commonly used in expression and purification of recombinant proteins. Attachment of a Trx tag to a target protein improves the solubility of that protein of interest. The inherent oxidoreductase activity of Trx also has an additional function of avoiding inclusion bodies. Antibodies targeting Trx can be used in the immunological detection and analyses of Trx-tagged proteins.