Role of Chaperon Co-Expression System in the Production of Recombinant Unnatural Proteins in Escherichia Coli

Here we evaluated the chaperon co-expression system for the production of unnatural recombinant proteins through selective pressure incorporation. In this study green fluorescent protein (GFP) was utilized as model proteins and L-homopropargylglycine (Hpg) was used as a model unnatural amino acid which is a methionine surrogate and can be incorporated into the methionine residues of recombinant protein. Initial experiments showed yields of L-Hpg containing GFP proteins were almost negligible compared to those of canonical amino acid incorporated natural proteins. These results indicated that incorporation of unnatural amino acid into protein affects the normal protein folding which immediately affects the protein functionality and productivity. Co-expression of the chaperons has been well reported to enhance the protein folding and preventing the aggregation from harsh environment condition. Hence, we expected that chaperon co-expression system will facilitate the production of unnatural recombinant protein production. Coexpression of DnaK-DnaJ-GrpE chaperons systems shows that the unnatural amino acid protein production was slightly higher than the wild type. However, chaperon systems GroEL and GroES completely failed to rescue the unnatural amino containing protein so the production yield of the unnatural protein was not improved. These results demonstrated that incorporation of unnatural amino acid tremendously influences the production yield of unnatural containing proteins in Escherichia coli. As well as chaperon teams are not critically involved in protein folding of unnatural amino acid containing protein and they failed to assist stability and prevent the disaggregation of proteins.