Dextran-grafted-PNIPAAm as an artificial chaperone for protein refolding

A temperature stimuli-responsive polymer, dextran-grafted-PNIPAAm (DGP), was prepared by radical polymerization using cerium nitrate as the initiator. The structure and the grafting ratio of DGP were determined by FT-IR and elemental analysis. The temperature-stimuli responsive behavior of DGP and the size of the DGP self-assemblies at different temperatures were determined by transmittance and dynamic light scattering, respectively. The use of DGP as an artificial chaperone to assist protein refolding in vitro was demonstrated using hen egg white lysozyme (lysozyme) and carbonic anhydrase bovine (CAB) as model proteins. It was shown that the hydrophobic interaction between DGP and the protein being refolded gave a significant reduction in the rate of protein aggregation and a slight reduction in the refolding rate, and consequently gave an improved refolding yield. Moreover, the refolding of lysozyme and CAB at a temperature gradient starting above the LCST of DGP and ending at a lower temperature, which make DGP change from hydrophobic to hydrophilic, gave a significant increase in the refolding yield compared to that carried out at a constant temperature. The process mechanism of DGP assisted protein refolding was presented and the importance of controlling the hydrophobicity of the solution environment for protein refolding was discussed.