Fractional factorial approach combining 4 Escherichia coli strains, 3 culture media, 3 expression temperatures and 5 N-terminal fusion tags for screening the soluble expression of recombinant proteins.

Producing recombinant proteins in Escherichia coli (E. coli) is generally performed using a trial and error approach with the different expression variables being tested independently from each other. As a consequence, variable interactions are lost which makes the trial and error approach quite time-consuming. In this paper, we report how switching from a trial and error to a fractional factorial approach allows testing in less than 2 weeks four expression variables (E. coli strains, culture media, expression temperatures and N-terminal fusion tags) in a single experiment. The method, called "Fusion-InFFact", was validated using four test proteins. In all cases, Fusion-InFFact allowed finding conditions for expressing high yields of soluble proteins. The method was originally set-up for high throughput structural genomics programs, but can be used in any recombinant protein expression project.