Strategies for optimization of heterologous protein expression in E. coli: Roadblocks and reinforcements.

E. coli is most preferred system used for the production of recombinant proteins in bacteria and the availability of improved genetic tools/methods are making it more valuable than ever. Major challenges faced by this expression system are the expression of unusually difficult/complex proteins with rare codons or membrane and toxic proteins. The proteins expressed either in large amount or hydrophobic in nature tend to form insoluble mass. Despite the appropriate expression system, some proteins express at very low level or not at all. Choosing the correct expression system/protocols are obligatory for the substantial expression of protein in the native form. A number of vectors, their compatible hosts and culture conditions can be used to express recombinant proteins in large amounts and in native form. Also, vectors with the fusion tags/chaperons facilitate protein expression in soluble fraction and assist in proper protein folding besides restoring the native structure of protein. The recovery of native proteins from insoluble inclusion bodies can be achieved by optimization of refolding conditions. In the present review, we discussed recent updates on prokaryotic expression system for successful heterologous gene expression in E. coli and focused on strategies to maximize the yields of native recombinant proteins.