Genetic design for facilitated production and recovery of recombinant proteins in Escherichia coli.
Genetic strategies have been used for more than two decades to improve bacterial bioprocesses and to simplify recovery procedures. Such strategies include the design of efficient expression vectors and the improvement of bacterial production strains in different ways, e.g. by deletion of protease genes or engineering for overexpression of rare-codon tRNAs, foldases or chaperones. Gene multimerization is another such principle that has proved beneficial to improve production yields. Genetic strategies have furthermore been exploited to facilitate recovery processes by adapting the product for a particular purification principle. In this area, affinity fusions have been commonly used, but other principles, such as modified isoelectric point (pI) or hydrophobic properties have also been successfully investigated. A recent drastic step forward in the use of gene technology to improve recovery processes for recombinant proteins is the introduction of combinatorial protein engineering to generate tailor-made product-specific affinity ligands. This strategy, which allows efficient recovery of a recombinant protein in its native form, is likely to be increasingly used also in industrial-scale bioprocesses, since novel protein ligands have been described that can be sanitized using common industrial cleaning-in-place procedures. The examples presented in this review make it evident that genetic strategies will be of utmost importance in the future for facilitating production and recovery of recombinant proteins.