Expanding the temperature range of biomimetic synthesis using a ferritin from the hyperthermophile Pyrococcus furiosus

Biological macromolecules, such as protein cages and viruses, have been shown to serve as excellent templates for the synthesis of nanoscale particles of inorganic materials that give rise to homogeneous properties. However, a limitation in using these molecules in these synthetic reactions has been the temperature stability of the biological template. It is hypothesized that the use of thermally stable proteins isolated from hyperthermophilic bacteria and archaea will overcome this limitation and expand the list of materials with interesting properties that are amenable to biomimetic synthesis. This study reports the synthesis of maghemite (gamma-Fe2O3) at elevated temperatures using a ferritin with extraordinary temperature stability from the hyperthermophilic archaeon Pyrococcus furiosus. Protein-mineral composites were characterized by dynamic light scattering, size exclusion chromatography, and transmission electron microscopy, which confirmed the successful encapsulation of the iron oxide particle in the interior of the ferritin. Magnetic characterization revealed saturation of the gamma-Fe2O3 nanoparticles at significantly lower field strengths than previously seen with mammalian ferritin-mineral composites. The observed behavior suggests the formation of well ordered, single domain particles within the archaeal ferritin. Electrostatic surface comparisons of the interior surface of human, horse spleen, and P. furiosus ferritins revealed a significant difference in the charge density between the mammalian and archaeal proteins which may influence the crystal structure of the material formed. These results demonstrate the utility of temperature stable protein cages as templates in the syntheses of desirable inorganic nanomaterials.