Application of short hydrophobic elastin-like polypeptides for expression and purification of active proteins

To investigate the application of short elastin-like polypeptides (ELPs) in the purification of bioactive proteins, short hydrophobic ELP[I](n) (n = 30, 40, 50) tags were constructed. Both the ELP[I](n) tags and the ELP[I](n)-Trx fusion proteins could be stably expressed in Escherichia coli and purified by inverse transition cycling, respectively. Total protein concentrations determined by BCA protein assay showed that the yield of the fusion proteins decreased with increasing ELP length. Measurements of the inverse transition temperature (T-t) of the ELP[I](n)-Trx under different salts or PEG8000 concentrations showed decreased T-t upon elevated concentrations; while, all the T(t)s were suitable for generating proteins from 4 to 37.5 oC. Furthermore, to identify a linker peptide for bioactive protein production without the need to remove the ELP[I](n) tag, the activity of eGFP protein fused with ELP[I](30) tag by either a poly-N or a G4S linker was quantified using a fluorescence spectrophotometer. The results indicated that the ELP[I](30)-eGFP fusion proteins with the poly-N linker showed higher fluorescence levels than those with the G4S linker. Our results demonstrated that short ELP[I](n) tags with low T-t were useful in protein expression and purification, and poly-N linker played the key role in producing bioactive proteins without the need to remove the ELPs.