Part:BBa_K1189025:Experience

Heavy chain human ferritin

This part is the heavy ferritin subunit from human ferritin, inspired by P02794 [UniParc]. Ferritin is ubiquitous across prokaryotic and eukaryotic systems and is used to buffer intracellular iron. This part, along with the light ferritin subunit, form a 24 multimeric iron sequestering nanoparticle (Chasteen et al., 1991). The difference between light ferritin is that this chain contains a ferroxidase centre. Protein domains which orient toward the core of ferritin molecules cause the oxidation of intracellular iron from Fe^2+ to Fe^3+ to initiate formation of a ferrihydrite core. (Chasteen et al., 1999). These nanoparticles are robust, remain stable at extreme pHs, and withstand temperature variations (Kim et al., 1999).

Figure 1. Ribbon visualization of a fully assembled ferritin protein.

Ferritin's utility in iGEM

Ferritin as a nanoparticle is interesting for other iGEM teams for two reasons. Firstly, its iron core can be replaced with other compounds to serve different functions. The iGEM Calgary 2013 demonstrated this by chemically modifying recombinant ferritin's iron core into a robust colourmetric reporter. Other intriguing applications include making ferritin’s iron core magnetically active as magnetoferritin (Jordan et al. 2013), using ferritin as a nanocage for other metals, or the incorporation of other reporters such as quantum dots (Naito et al. 2013) (Figure 2).

Figure 2. Chemically modifying the iron core of ferritin allows ferritin to be moulded to fit a wide magnitude of applications. Additionally the ferritin subunits can act as a nanocage to encapsulate completely new cores.

Secondly, the ferritin nanoparticle is useful for iGEM teams as a self-assembling and spherical protein scaffold. Each of the 24 subunits forming ferritin can be fused to proteins of interest, such that when the nanoparticle assembles, proteins surround the ferritin sphere (Kim et al., 2011). The iGEM Calgary 2013 team demonstrated this by binding DNA sensing proteins, TALEs, as part of their FerriTALE sensor. The Calgary team also constructed ferritin subunits with a coiled-coil linker system so that other teams can scaffold proteins to E-coil ferritin (BBa_K1189018, BBa_K1189019, BBa_K1189020, BBa_K1189037). See Figure 3 for a demonstration of these applications.

Figure 3. Using the E and K coils in combination with ferritin as a scaffold system allows the creation of brand new FerriTALEs or protein scaffolds.

References

Chasteen, N. D., & Harrison, P. M. (1999). Mineralization in ferritin: an efficient means of iron storage. Journal of structural biology, 126(3), 182-194.

Clavijo Jordan, V., Caplan, M. R., & Bennett, K. M. (2010). Simplified synthesis and relaxometry of magnetoferritin for magnetic resonance imaging. Magnetic Resonance in Medicine, 64(5), 1260-1266.

Kim, S. E., Ahn, K. Y., Park, J. S., Kim, K. R., Lee, K. E., Han, S. S., & Lee, J. (2011). Fluorescent ferritin nanoparticles and application to the aptamer sensor. Analytical chemistry, 83(15), 5834-5843.

Naito, M., Iwahori, K., Miura, A., Yamane, M., & Yamashita, I. (2010). Circularly polarized luminescent CdS quantum dots prepared in a protein nanocage. Angewandte Chemie International Edition, 49(39), 7006-7009.

User Reviews

iGEM Calgary 2013: The heavy ferritin gene sequence as stated with this basic part was functional when expressed as N-terminal fusion proteins (BBa_K1189018, BBa_K1189021, BBa_K1189037) with the light ferritin subunit. We did not explore expressibility of heavy ferritin chain in isolation and hope to see other teams take this on.

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