Polysaccharide nanogel–cyclodextrin system as an artificial chaperone for in vitro protein synthesis of green fluorescent protein

Polysaccharide nanogels have been demonstrated to aid the refolding processes of chemically or thermally denatured proteins, a function that is similar to that of natural molecular chaperones. In this study, we examined the possibilities of using the nanogel chaperone system to mediate protein folding in a cell-free (in vitro) protein synthesis system containing transcription/ translation factors. High-performance liquid chromatography showed that a polysaccharide nanogel comprising cholesteryl group-bearing pullulan (CHP) trapped unfolded or partially folded green fluorescent protein (GFP) expressed in the cell-free system. The protein release and refolding processes, which are induced by ATP in natural molecular chaperone systems, were also simulated by methyl-b-cyclodextrin (M-b-CD). The CHP nanogels dissociate on complexation with M-b-CD to yield dissociated CHP. Thus, the dissociation of the CHP nanogel–protein complex subsequently allows for the release and folding of GFP. The folding kinetics in the presence of the CHP nanogel and M-b-CD was comparable to that of spontaneous folding in the absence of CHP/M-b-CD, indicating that the CHP nanogels did not affect protein synthesis in the cell-free system, providing correctly folded active proteins. Polymer Journal (2010) 42, 823–828; doi:10.1038/pj.2010.73; published online 18 August 2010