A Novel Hyperthermostable Recombinant Protein Nanocage

Background: Ferritin has an important role in iron storage in the cells, and due to its nanocage structure and self-assembly properties, it has wide application prospects in nanobiotechnology.

Methods: The maize (Zea mays) ferritin gene ZmFer1 was cloned and expressed in Escherichia coli BL21 (DE3) for the first time. Change in macromolecular structure of ZmFer1 ferritin due to heat treatment was investigated using native PAGE electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Change in the secondary structures of the protein was evaluated using circular dichroism spectroscopy. Moreover, alteration in the conformation of the protein was evaluated using UV-absorption spectra and intrinsic fluorescence spectra. The melting temperature (Tm) of ZmFer1 was obtained using differential scanning calorimetry (DSC). Finally, the effect of heat on the function of ZmFer1 was assessed by iron loading ability.

Results: The purified ZmFer1 protein showed a homopolymer nanocage structure. The results of native PAGE electrophoresis, DLS, and TEM techniques showed that ZmFer1 protein nanocage is stable to heat treatment up to 90 °C, and some of the protein nanocages retain their macromolecular structures even at 100 °C in liquid aqueous solution. Based on the DSC results, ZmFer1 protein nanocage had a Tm of 81.9 °C. After treatment at 100 °C, stable ZmFer1 protein nanocages were able to store iron atoms.

Conclusion: Recombinant ZmFer1 ferritin with a Tm > 80°C is a hyperthermostable protein nanocage. The results of this study are beneficial for the development of protein nanocages that are stable under extreme temperature conditions, as well as application of ZmFer1 in nanobiotechnology, biomaterials, and biomedical fields.