Purification of a crystallin domain of Yersinia crystallin from inclusion bodies and its comparison to native protein from the soluble fraction.

It has been established that many heterologously produced proteins in E. coli accumulate as insoluble inclusion bodies. Methods for protein recovery from inclusion bodies involve solubilization using chemical denaturants such as urea and guanidine hydrochloride, followed by removal of denaturant from the solution to allow the protein to refold. In this work, we applied on-column refolding and purification to the second crystallin domain D2 of Yersinia crystallin isolated from inclusion bodies. We also purified the protein from the soluble fraction (without using any denaturant) to compare the biophysical properties and conformation, although the yield was poor. On-column refolding method allows rapid removal of denaturant and refolding at high protein concentration, which is a limitation in traditionally used methods of dialysis or dilution. We were also able to develop methods to remove the co-eluting nucleic acids during chromatography from the protein preparation. Using this protocol, we were able to rapidly refold and purify the crystallin domain using a two-step process with high yield. We used biophysical techniques to compare the conformation and calcium-binding properties of the protein isolated from the soluble fraction and inclusion bodies.