A simple and effective strategy for solving the problem of inclusion bodies in recombinant protein technology: His-tag deletions enhance soluble expression.

The formation of inclusion bodies (IBs) in recombinant protein biotechnology has become one of the most frequent undesirable occurrences in both research and industrial applications. So far, the pET System is the most powerful system developed for the production of recombinant proteins when Escherichia coli is used as the microbial cell factory. Also, using fusion tags to facilitate detection and purification of the target protein is a commonly used tactic. However, there is still a large fraction of proteins that cannot be produced in E. coli in a soluble (and hence functional) form. Intensive research efforts have tried to address this issue, and numerous parameters have been modulated to avoid the formation of inclusion bodies. However, hardly anyone has noticed that adding fusion tags to the recombinant protein to facilitate purification is a key factor that affects the formation of inclusion bodies. To test this idea, the industrial biocatalysts uridine phosphorylase from Aeropyrum pernix K1 and (+)-γ-lactamase and (-)-γ-lactamase from Bradyrhizobium japonicum USDA 6 were expressed in E. coli by using the pET System and then examined. We found that using a histidine tag as a fusion partner for protein expression did affect the formation of inclusion bodies in these examples, suggesting that removing the fusion tag can promote the solubility of heterologous proteins. The production of soluble and highly active uridine phosphorylase, (+)-γ-lactamase, and (-)-γ-lactamase in our results shows that the traditional process needs to be reconsidered. Accordingly, a simple and efficient structure-based strategy for the production of valuable soluble recombinant proteins in E. coli is proposed.