Influence of medium components on the expression of recombinant lipoproteins in Escherichia coli.

Bacterial lipoproteins are crucial antigens for protective immunity against bacterial pathogens. Expression of exogenous lipoproteins in Escherichia coli at high levels is thought to be an extremely difficult endeavor because it frequently results in incomplete or absent lipid modification. Previously, we identified a fusion sequence (D1) from a Neisseria meningitidis lipoprotein that induced a non-lipidated protein, E3 (the domain III of the dengue virus envelope protein), to become lipidated. However, without optimizing the growth conditions, some of the D1-fusion proteins were not lipidated. Here, we report the influence of medium components on the expression of recombinant lipoproteins in E. coli. For high-level expression of mature lipoproteins in the C43 (DE3) strain, M9 medium was better than M63 and the rich medium. Furthermore, we analyzed the influence of other media factors (including nitrogen and carbon sources, phosphate, ferrous ions, calcium, magnesium, and pH) on the levels of lipoprotein expression. The results showed that excess nitrogen sources and phosphate in M9 medium could increase the amount of immature lipoproteins, and glucose was a better carbon source than glycerol for expressing mature lipoproteins. We also found that lipoproteins tended to be completely processed in the alkaline environment, even in the nutrient-rich medium. Additional constructs expressing different immunogens or lipid signal peptides as targets were also utilized, demonstrating that these targets could be expressed as completely mature lipoproteins in the M9 medium but not in the rich medium. Our results provide the useful information for expressing mature exogenous lipoproteins in E. coli.