Construction of ferritin hydrogels utilizing subunit–subunit interactions

Abstract

Various proteins form nanostructures exhibiting unique functions, making them attractive as next-generation materials. Ferritin is a hollow spherical protein that incorporates iron ions. Here, we found that hydrogels are simply formed from concentrated apoferritin solutions by acid denaturation and subsequent neutralization. The water content of the hydrogel was approximately 80%. The apoferritin hydrogel did not decompose in the presence of 1 M HCl, 2-mercaptoethanol, or methanol but was dissolved in the presence of 1 M NaOH, by heating at 80°C, or by treatment with trypsin or 6 M guanidine hydrochloride. The Young’s modulus of the hydrogel was 20.4 ± 12.1 kPa according to local indentation experimentes using atomic force microscopy, indicating that the hydrogel was relatively stiff. Transition electron microscopy measurements revealed that a fibrous network was constructed in the hydrogel. The color of the hydrogel became yellow-brown upon incubation in the presence of Fe3+ ions, indicating that the hydrogel adsorbed the Fe3+ ions. The yellow-brown color of the Fe3+-adsorbed hydrogel did not change upon incubation in pure water, whereas it became pale by incubating it in the presence of 100 mM ethylenediaminetetraacetic acid (EDTA). The apoferritin hydrogel also adsorbed Co2+ and Cu2+ ions and released them in the presence of EDTA, while it adsorbed less Ni2+ ions; more Fe3+ ions adsorbed to the apoferritin hydrogel than other metal ions, indicating that the hydrogel keeps the iron storage characteristic of ferritin. These results demonstrate a new property of ferritin: the ability to form a hydrogel that can adsorb/desorb metal ions, which may be useful in designing future biomaterials.

Hydrogels: Properties and Applications in Biomedicine

“…The physical crosslinking in hydrogels includes hydrogen bonding, amphiphilic graft, block polymers formation, crystallization, ionic interactions, and protein interactions. [100][101][102][103][104][105][106][107][108][109][110][111][112]. The hydrogen bonding is present between molecules containing N-H, O-H, or F-H functional groups.…”

Real-Space Visualization of Charged Polymer Network of Hydrogel by Double Network Strategy and Mineral Staining

“…Moreover, the conventional hydrogel network, which consists of light elements, such as C, N, O, and H, must be stained. The general method to enhance the electron density is electron staining with heavy-element compounds such as uranyl acetate , and phosphotungstic acid. , Although this method allows the observation of self-assembled peptide nanofibers − and refolded spherical protein complex networks, direct visualizations of individual polymer chains within synthetic hydrogels have not been achieved using this approach. Synthetic polymer strands are thin, flexible, and susceptible to aggregation during staining or resinification.…”