Expression hosts

    Since its first description in 1886 by Escherich, the gram-negative bacterium Escherichia coli has become the prokaryotic model organism and work horse in many labs, amongst which ours. The majority of prokaryotic membrane protein structures in the PDB result from protein produced in E. coli. Nevertheless, establishing an overexpression system in E. coli is not trivial and regularly fails. Rather than screening several E. coli strains, we prefer to screen broader for overexpression using a completely different host, the gram-positive bacterium Lactococcus lactis, instead. L. lactis is cultivated easily and as a consequence of its extensive use in dairy industry, its growth, physiology and genetic manipulation have been well described. Many examples of membrane proteins well-overexpressed in L. lactis are available, making L. lactis an attractive alternative to E. coli.

    Concerning membrane protein overexpression, important differences between both hosts are: the composition of the machinery involved in membrane protein insertion, the lipid composition of the membrane, codon usage (lactococcal DNA is more AT-rich than E. coli), and the absence of a disulfide isomerase system in L. lactis. In addition, the stress of overexpressing a specific membrane protein can differ significantly between both hosts. For both expression hosts, well-tunable promoter systems are available.

    Relevant Publication

    Geertsma ER, Poolman B. (2010)
    Production of membrane proteins in Escherichia coli and Lactococcus lactis.

    Methods Mol Biol. 2010;601:17-38.