(9g) Elastin-Like Polypeptide Tag Length Effect On Protein Expression and Purification

Recombinant protein technology has enabled the expression of fusion proteins that can be purified in bacterial systems with the use of purification tags. In particular, the elastin-like polypeptide (ELP) precipitation tag in the presence of a self-cleaving intein protein domain allows the non-chromatographic purification of a target protein with only a change in salt concentration and pH. Shortening the ELP tag length has the potential to increase expression by freeing the energy that would be required to synthesize the large ELP repetitive protein sequence.  An increase in production yield of a given protein would thus be expected when decreasing the ELP tag length. Furthermore, the optimal ELP tag length needed may be affected by the size and solubility of the protein product fused with the tag. In this study, the effect of five different ELP tag sizes in product yield was examined in the expression and purification of several proteins, including β-galactosidase and β-lactamase. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) qualitatively suggested the success of each purification. The corresponding activity and Bradford assays were then used to confirm these results quantitatively. Finally, studies including a wider range of salt concentrations and a wider selection of target proteins with varying hydrophobicity can help elucidate the relationship between the target protein fused to the ELP-intein system and the ELP tag length required for its successful purification.