Biotechnological applications of periplasmic expression in E. coli

Expression of recombinant proteins outside the cytoplasm was pioneered over 20 years ago in bacterial and yeast systems [1-3], opening the way for its current use in a variety of biotechnological applications [4]. The bacterium Escherichia coli remains the preferred host for the extracytoplasmic expression of recombinant proteins because of its compartmentalized cell envelope, which comprises the cytoplasmic and outer membrane separated by the periplasmic space [5]. Production of recombinant proteins in the periplasm offers in some cases important advantages over their cytoplasmic expression because it improves protein folding, reduces proteolytic degradation and facilitates purification [6]. Additionally, many (potential) substrates are able to cross the outer membrane unlike the cytoplasmic membrane. The increased substrate accessibility offered by periplasmic expression is a major advantage that is exploited in library screening and whole-cell biocatalysis [7]. Here, I will discuss recent progress in the periplasmic expression of recombinant proteins in E. coli with a focus on its use in library screening, protein engineering and whole-cell biocatalysis.