Expression and purification of thioredoxin fusion proteins.

This unit describes a gene fusion expression system that uses thioredoxin, the product of the Escherichia coli trxA gene, as the fusion partner. The system is particularly useful for high-level production of soluble fusion proteins in the E. coli cytoplasm; in many cases heterologous proteins produced as thioredoxin fusion proteins are correctly folded and display full biological activity. Protein fusions to His-patch Trx can usually be purified in a single step from cell lysates. Additional protocols describe E. coli cell lysis using a French pressure cell and fractionation, osmotic release of thioredoxin fusion proteins from the E. coli cytoplasm, and heat treatment to purify some thioredoxin fusion proteins.