Nanoparticles of unmodified titanium dioxide facilitate protein refolding

Titanium dioxide (TiO2) nanoparticles (similar to 10 nm) were found to effectively assist refolding of thermally denatured proteins alpha-chymotrypsin, RNase A and papain. The isoelectric points (pI) of the enzymes and elution of the refolded enzymes from the nanoparticles after about one hour incubation with salt show that the protein-nanoparticle interaction was predominantly electrostatic in nature. The refolded enzymes regained nearly 100% activity in all the three cases and their CD spectra were similar to corresponding CD spectra of these enzymes in their native form. Dynamic light scattering (DLS) shows that complexes between TiO2 nanoparticles and denatured proteins reached their maximum sizes in the same time period (i.e., 1 hour) which was optimum for regaining the biological activity during nanoparticle assisted refolding.