Impact of genetic engineering on downstream processing of proteins produced in E. coli

Genetic engineering can be used to give a protein properties that are advantageous for downstream processing. Many heterologous proteins are degraded at high rates by proteases. Depending on which type of proteolytic degradation is encountered the strategy may be different: induction of inclusion bodies, change of the amino acid sequence in the sensitive site of the product, or protection by fusion of the product with other proteins. The number of unit operations needed to purify a protein may be reduced by addition of other polypeptides or amino acids to the product. Affinity chromatography, immobilized metal ion affinity chromatography, and extraction in aqueous two-phase systems are unit operations which can be made more versatile by the fusion technique.