Recombinant Expression and Overproduction of Transmembrane β-Barrel Proteins

Transmembrane β-barrel proteins reside in the outer membrane of Gram-negative bacteria and are thus in direct contact with the environment. Because of that, they are involved in many key processes stretching from cellular survival to virulence. Hence, they are an attractive target for the development of novel antimicrobials, in addition to being of fundamental biological interest. To study this class of proteins, they are often required to be expressed in Escherichia coli. Recombinant expression of β-barrel proteins can be achieved using two fundamentally different strategies. The first alternative uses a complete coding sequence that includes a signal peptide for targeting the protein to its native cellular location, the bacterial outer membrane. The second alternative omits the signal peptide in the gene, leading to mislocalization and aggregation of the protein in the bacterial cytoplasm. These aggregates, called inclusion bodies, can be solubilized and the protein can be folded into its native form in vitro. In this chapter, we present example protocols for both strategies and discuss their advantages and disadvantages.