Expression platforms for producing eukaryotic proteins: a comparison of E. coli cell-based and wheat germ cell-free synthesis, affinity and solubility tags, and cloning strategies.

Vectors designed for protein production in Escherichia coli and by wheat germ cell-free translation were tested using 21 well-characterized eukaryotic proteins chosen to serve as controls within the context of a structural genomics pipeline. The controls were carried through cloning, small-scale expression trials, large-scale growth or synthesis, and purification. Successfully purified proteins were also subjected to either crystallization trials or (1)H-(15)N HSQC NMR analyses. Experiments evaluated: (1) the relative efficacy of restriction/ligation and recombinational cloning systems; (2) the value of maltose-binding protein (MBP) as a solubility enhancement tag; (3) the consequences of in vivo proteolysis of the MBP fusion as an alternative to post-purification proteolysis; (4) the effect of the level of LacI repressor on the yields of protein obtained from E. coli using autoinduction; (5) the consequences of removing the His tag from proteins produced by the cell-free system; and (6) the comparative performance of E. coli cells or wheat germ cell-free translation. Optimal promoter/repressor and fusion tag configurations for each expression system are discussed.