Relationship between Protein Expression Pattern and Host Metabolome Perturbation as Monitored by Two‐Dimensional NMR Spectroscopy

In producing large amounts of heterologous proteins, researchers most often use Escherichia coli as a host thanks to its extensively studied genetics, simple growth procedure, and low cost. However, the desired protein is often produced only in a form of inclusion bodies. Researchers have tried to devise a way to circumvent such a problem, and the ones using fusion partners seem to be the most successful. Based on our previous observation that the host metabolome was related to the outcomes of protein expression patterns, we proceeded to perturb the metabolome by applying a salt stress to see if we could shake up metabolite compositions to make them better suited for soluble expression of the target protein. We examined a subset of the metabolites which had been partially labeled with input 13C‐glucose. We tested 11 genes under 4 different NaCl concentrations, and identified 18 metabolites using the heteronuclear single quantum coherence NMR experiment. Most of the proteins kept their expression profiles unchanged, but two proteins were converted from inclusion bodies to a soluble form with increased NaCl concentration. Through the statistical analysis, we could identify a region where the soluble protein production was favored in the metabolite space. We hope that this work would provide an alternative strategy to produce the recombinant proteins in their soluble or native forms, not only in E. coli but also in other hosts.