Selecting an appropriate method for expressing a recombinant protein.

Recombinant proteins are important tools for studying biological processes. Generating a recombinant protein requires the use of an expression system. Selection of an appropriate expression system is dependent on the characteristics and intended application of the recombinant protein and is essential to produce sufficient quantities of the protein. Over the last 30 years, there have been considerable advances in the technologies for expressing recombinant proteins. In this chapter the unique characteristics of four commonly used expression systems, Escherichia coli, Pichia pastoris, baculovirus/insect cell, and mammalian cells are described. The E. coli system is a rapid method for expressing proteins but lacks many of the posttranslational modifications found in eukaryotes. The capacity of E. coli for protein folding and forming disulfide bonds is not sufficient for many recombinant proteins although there are a number of tools developed to overcome these limitations. In contrast to E. coli, the eukaryotic P. pastoris, baculovirus/insect cell, and mammalian systems promote good protein folding and many posttranslational modifications. How the characteristics and the downstream application of a recombinant protein can influence the choice of an expression system is then reviewed.